fpc/compiler/ogelf.pas

{
    Copyright (c) 1998-2006 by Peter Vreman

    Contains the binary elf writer

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

 ****************************************************************************
}
unit ogelf;

{$i fpcdefs.inc}

interface

    uses
       { common }
       cclasses,globtype,
       { target }
       systems,
       { assembler }
       aasmbase,assemble,
       { ELF definitions }
       elfbase,
       { output }
       ogbase,
       owbase;

    type
{$ifdef cpu64bitaddr}
      TElfsechdr = TElf64sechdr;
{$else cpu64bitaddr}
      TElfsechdr = TElf32sechdr;
{$endif cpu64bitaddr}

       TElfObjSection = class(TObjSection)
       public
          shstridx,
          shtype,
          shflags,
          shlink,
          shinfo,
          shentsize : longint;
          constructor create(AList:TFPHashObjectList;const Aname:string;Aalign:longint;Aoptions:TObjSectionOptions);override;
          constructor create_ext(aobjdata:TObjData;const Aname:string;Ashtype,Ashflags:longint;Aalign:longint;Aentsize:longint);
          constructor create_reloc(aobjdata:TObjData;const Aname:string;allocflag:boolean);
          procedure writeReloc_internal(aTarget:TObjSection;offset:aword;len:byte;reltype:TObjRelocationType);override;
       end;

       TElfSymtabKind = (esk_obj,esk_exe,esk_dyn);

       TElfSymtab = class(TElfObjSection)
       public
         kind: TElfSymtabKind;
         fstrsec: TObjSection;
         symidx: longint;
         tlsbase: aword;
         constructor create(aObjData:TObjData;aKind:TElfSymtabKind);reintroduce;
         procedure writeSymbol(objsym:TObjSymbol;nameidx:longword=0);
         procedure writeInternalSymbol(avalue:aword;astridx:longword;ainfo:byte;ashndx:word);
       end;

       TElfObjData = class(TObjData)
       public
         ident: TElfIdent;
         flags: longword;
{$ifdef mips}
         gp_value: longword;
{$endif mips}
         constructor create(const n:string);override;
         function  sectionname(atype:TAsmSectiontype;const aname:string;aorder:TAsmSectionOrder):string;override;
         procedure CreateDebugSections;override;
         procedure writereloc(data:aint;len:aword;p:TObjSymbol;reltype:TObjRelocationType);override;
       end;

       TElfObjectOutput = class(tObjOutput)
       private
         symtabsect: TElfSymtab;
         shstrtabsect: TElfObjSection;
         procedure createrelocsection(s:TElfObjSection;data:TObjData);
         procedure createshstrtab(data:TObjData);
         procedure createsymtab(data: TObjData);
         procedure writesectionheader(s:TElfObjSection);
         procedure section_write_symbol(p:TObject;arg:pointer);
         procedure section_count_sections(p:TObject;arg:pointer);
         procedure section_create_relocsec(p:TObject;arg:pointer);
         procedure section_write_sechdr(p:TObject;arg:pointer);
       protected
         function writedata(data:TObjData):boolean;override;
       public
         constructor Create(AWriter:TObjectWriter);override;
       end;

       TElfAssembler = class(tinternalassembler)
         constructor create(info: pasminfo; smart:boolean);override;
       end;

       PSectionRec=^TSectionRec;
       TSectionRec=record
         sec: TObjSection;
         relocpos: aword;
         relocs: longint;
         relentsize: longint;
       end;

       TElfsecheaderarray=array of TElfsechdr;
       TObjSymbolClass=class of TObjSymbol;

       TElfObjInput=class(TObjInput)
       private
         FSecTbl: PSectionRec;
         FSymTbl: PPointer;
         FLoaded: PBoolean;
         shdrs: TElfsecheaderarray;
         nsects: longword;
         shoffset: aword;
         shstrndx: longword;
         symtabndx: longword;
         shstrtab: PChar;
         strtab: PChar;
         shstrtablen: longword;
         strtablen: longword;
         symtaboffset: aword;
         syms: longword;
         localsyms: longword;
         symversions: PWord;
         dynobj: boolean;
         CObjSymbol: TObjSymbolClass;
         verdefs: TFPHashObjectList;
         function LoadHeader(out objdata:TObjData):boolean;
         procedure LoadSection(const shdr:TElfsechdr;index:longint;objdata:TObjData);
         procedure LoadRelocations(const secrec:TSectionRec);
         procedure LoadSymbols(objdata:TObjData;count,locals:longword);
         procedure LoadDynamic(const shdr:TElfsechdr;objdata:TObjData);
       public
         constructor Create;override;
         destructor Destroy;override;
         function  ReadObjData(AReader:TObjectreader;out objdata:TObjData):boolean;override;
         class function CanReadObjData(AReader:TObjectreader):boolean;override;
         function CreateSection(const shdr:TElfsechdr;index:longint;objdata:TObjData;
           out secname:string):TElfObjSection;
         function ReadBytes(offs:longint;out buf;len:longint):boolean;
       end;

       TElfVersionDef = class(TFPHashObject)
       public
         index: longword;
       end;

       TElfDynamicObjData = class(TElfObjData)
       private
         FVersionDefs: TFPHashObjectList;
       public
         soname_strofs: longword;
         vernaux_count: longword;
         constructor create(const n:string);override;
         destructor destroy;override;
         property versiondefs:TFPHashObjectList read FVersionDefs;
       end;

       TVersionedObjSymbol = class(TObjSymbol)
       private
         FVersion: TElfVersionDef;
       public
         property version: TElfVersionDef read FVersion write FVersion;
       end;

       TRelocNameProc=function(reltyp:byte):string;
       TEncodeRelocProc=function(objrel:TObjRelocation):byte;
       TLoadRelocProc=procedure(objrel:TObjRelocation);
       TLoadSectionProc=function(objinput:TElfObjInput;objdata:TObjData;const shdr:TElfsechdr;shindex:longint):boolean;
       TEncodeFlagsProc=function:longword;
       TDynamicReloc=(
         dr_relative,
         dr_glob_dat,
         dr_jump_slot,
         dr_copy,
         dr_irelative
       );

       TElfTarget=record
         max_page_size: longword;
         exe_image_base: longword;
         machine_code: word;
         relocs_use_addend: boolean;
         dyn_reloc_codes: array[TDynamicReloc] of byte;
         relocname: TRelocNameProc;
         encodereloc: TEncodeRelocProc;
         loadreloc: TLoadRelocProc;
         loadsection: TLoadSectionProc;
         encodeflags: TEncodeFlagsProc;
       end;


       TElfExeSection=class(TExeSection)
       public
         secshidx  : longword; { index of the section header }
         shstridx,
         shtype,
         shflags,
         shlink,
         shinfo,
         shentsize : longword;
         procedure AddObjSection(objsec:TObjSection;ignoreprops:boolean=false);override;
       end;

       TElfSegment=class
       public
         ptype: longword;
         pflags: longword;
         DataPos: aword;
         DataSize: aword;
         MemPos: aword;
         MemSize: aword;
         align: longword;
         //physaddr: aword;
         FSectionList: TFPObjectList;
         constructor Create(atype,aflags,aalign:longword);
         destructor Destroy; override;
         procedure Add(exesec:TExeSection);
       end;

       TElfExeOutput=class(TExeOutput)
       private
         segmentlist: TFPObjectList;
         textseg,
         dataseg,
         noteseg,
         phdrseg: TElfSegment;
         shstrtabsect: TElfObjSection;
         symtab: TElfSymtab;
         shoffset: aword;
         gotwritten: boolean;
         { dynamic linking }
         dynsymnames: Plongword;
         dynsymtable: TElfSymtab;
         interpobjsec: TObjSection;
         FInterpreter: pshortstring;
         verneedcount,
         verdefcount: longword;
         symversec,
         verdefsec,
         verneedsec,
         hashobjsec: TElfObjSection;
         neededlist: TFPHashList;
         dyncopysyms: TFPObjectList;
         preinitarraysec,
         initarraysec,
         finiarraysec: TObjSection;
         function AttachSection(objsec:TObjSection):TElfExeSection;
         function CreateSegment(atype,aflags,aalign:longword):TElfSegment;
         procedure WriteHeader;
         procedure WriteDynamicSymbolsHash;
         procedure WriteVersionSections;
         procedure WriteDynamicTags;
         procedure FinishDynamicTags;
         procedure exesection_write_header(p:TObject;arg:Pointer);
         procedure segment_write_header(p:TObject;arg:Pointer);
         procedure mempos_segment(seg:TElfSegment);
         procedure datapos_segment(seg:TElfSegment);
         procedure MapSectionsToSegments;
         procedure WriteStaticSymtable;
         procedure WriteShstrtab;
         procedure FixupSectionLinks;
         procedure InitDynlink;
         procedure OrderOrphanSections;
       protected
         dynamiclink: boolean;
         hastextrelocs: boolean;
         gotsymbol: TObjSymbol;
         dynsymlist: TFPObjectList;
         dynamicsec,
         gotobjsec: TObjSection;
         dynbssobjsec,
         pltobjsec,
         gotpltobjsec,
         pltrelocsec,
         ipltrelocsec,
         dynrelocsec: TElfObjSection;
         dynreloclist: TFPObjectList;
         tlsseg: TElfSegment;
         relative_reloc_count: longint;
         gotsize: aword;
         dynrelsize: aword;
         procedure PrepareGOT;virtual;
         function AllocGOTSlot(objsym: TObjSymbol):boolean;virtual;
         procedure CreateGOTSection;virtual;
         procedure make_dynamic_if_undefweak(exesym:TExeSymbol);
         procedure WriteDynRelocEntry(dataofs:aword;typ:byte;symidx:aword;addend:aword);
         procedure CreatePLT;virtual;
         procedure WriteFirstPLTEntry;virtual;abstract;
         procedure WritePLTEntry(exesym:TExeSymbol);virtual;
         procedure WriteIndirectPLTEntry(exesym:TExeSymbol);virtual;
         procedure WriteTargetDynamicTags;virtual;
         procedure GOTRelocPass1(objsec:TObjSection;var idx:longint);virtual;abstract;
         procedure ReportNonDSOReloc(reltyp:byte;objsec:TObjSection;ObjReloc:TObjRelocation);
         procedure ReportRelocOverflow(reltyp:byte;objsec:TObjSection;ObjReloc:TObjRelocation);
         procedure WriteDynTag(aTag:longword;aValue:longword);
         procedure WriteDynTag(aTag:longword;aSection:TObjSection;aOffs:aword=0);
         procedure Do_Mempos;virtual;
       public
         constructor Create;override;
         destructor Destroy;override;
         procedure Load_Start;override;
         procedure Load_DynamicObject(ObjData:TObjData;asneeded:boolean);override;
         procedure Order_Start;override;
         procedure Order_end;override;
         procedure AfterUnusedSectionRemoval;override;
         procedure MemPos_Start;override;
         procedure MemPos_ExeSection(const aname:string);override;
         procedure DataPos_Start;override;
         procedure DataPos_ExeSection(const aname:string);override;
         function writeData:boolean;override;
         procedure GenerateLibraryImports(ImportLibraryList:TFPHashObjectList);override;
         property interpreter:pshortstring read FInterpreter write FInterpreter;
       end;

     var
       ElfExeOutputClass: TExeOutputClass;
       ElfTarget: TElfTarget;

     const
       { Bits of TObjSymbol.refs field }
       symref_plt = 1;
       symref_from_text = 2;



implementation

      uses
        SysUtils,
        verbose,
        export,expunix,
        cutils,globals,fmodule,owar;

    const
      symbolresize = 200*18;

{$ifdef cpu64bitaddr}
      const
        ELFCLASS = ELFCLASS64;
      type
        telfheader = telf64header;
        telfreloc = telf64reloc;
        telfsymbol = telf64symbol;
        telfproghdr = telf64proghdr;
        telfdyn = telf64dyn;

      function ELF_R_INFO(sym:longword;typ:byte):qword;inline;
        begin
          result:=(qword(sym) shl 32) or typ;
        end;

{$else cpu64bitaddr}
      const
        ELFCLASS = ELFCLASS32;
      type
        telfheader = telf32header;
        telfreloc = telf32reloc;
        telfsymbol = telf32symbol;
        telfproghdr = telf32proghdr;
        telfdyn = telf32dyn;

      function ELF_R_INFO(sym:longword;typ:byte):longword;inline;
        begin
          result:=(sym shl 8) or typ;
        end;
{$endif cpu64bitaddr}


{****************************************************************************
                                Helpers
****************************************************************************}

    procedure encodesechdrflags(aoptions:TObjSectionOptions;out AshType:longint;out Ashflags:longint);
      begin
        { Section Type }
        if oso_strings in aoptions then
          AshType:=SHT_STRTAB
        else if not(oso_data in aoptions) then
          AshType:=SHT_NOBITS
        else if oso_note in aoptions then
          AshType:=SHT_NOTE
        else if oso_arm_attributes in aoptions then
          AshType:=SHT_ARM_ATTRIBUTES
        else
          AshType:=SHT_PROGBITS;
        { Section Flags }
        Ashflags:=0;
        if oso_load in aoptions then
          Ashflags:=Ashflags or SHF_ALLOC;
        if oso_executable in aoptions then
          Ashflags:=Ashflags or SHF_EXECINSTR;
        if oso_write in aoptions then
          Ashflags:=Ashflags or SHF_WRITE;
        if oso_threadvar in aoptions then
          Ashflags:=Ashflags or SHF_TLS;
      end;


    procedure decodesechdrflags(AshType:longint;Ashflags:longint;out aoptions:TObjSectionOptions);
      begin
        aoptions:=[];
        { Section Type }
        if AshType<>SHT_NOBITS then
          include(aoptions,oso_data);
        if AshType=SHT_STRTAB then
          include(aoptions,oso_strings);
        { Section Flags }
        if Ashflags and SHF_ALLOC<>0 then
          include(aoptions,oso_load);
        if Ashflags and SHF_WRITE<>0 then
          include(aoptions,oso_write);
        if Ashflags and SHF_EXECINSTR<>0 then
          include(aoptions,oso_executable);
        if Ashflags and SHF_TLS<>0 then
          include(aoptions,oso_threadvar);
      end;


{****************************************************************************
                               TElfObjSection
****************************************************************************}

    constructor TElfObjSection.create(AList:TFPHashObjectList;const Aname:string;Aalign:longint;Aoptions:TObjSectionOptions);
      begin
        inherited create(AList,Aname,Aalign,aoptions);
        index:=0;
        shstridx:=0;
        encodesechdrflags(aoptions,shtype,shflags);
        shlink:=0;
        shinfo:=0;
        if name='.stab' then
          shentsize:=sizeof(TObjStabEntry);
      end;


    constructor TElfObjSection.create_ext(aobjdata:TObjData;const Aname:string;Ashtype,Ashflags:longint;Aalign:longint;Aentsize:longint);
      var
        aoptions : TObjSectionOptions;
      begin
        decodesechdrflags(Ashtype,Ashflags,aoptions);
        inherited create(aobjdata.ObjSectionList,Aname,Aalign,aoptions);
        objdata:=aobjdata;
        index:=0;
        shstridx:=0;
        shtype:=AshType;
        shflags:=AshFlags;
        shentsize:=Aentsize;
      end;


    const
      relsec_prefix:array[boolean] of string[5] = ('.rel','.rela');
      relsec_shtype:array[boolean] of longword = (SHT_REL,SHT_RELA);

    constructor TElfObjSection.create_reloc(aobjdata:TObjData;const Aname:string;allocflag:boolean);
      begin
        create_ext(aobjdata,
          relsec_prefix[ElfTarget.relocs_use_addend]+aname,
          relsec_shtype[ElfTarget.relocs_use_addend],
          SHF_ALLOC*ord(allocflag),
          sizeof(pint),
          (2+ord(ElfTarget.relocs_use_addend))*sizeof(pint));
      end;


    procedure TElfObjSection.writeReloc_internal(aTarget:TObjSection;offset:aword;len:byte;reltype:TObjRelocationType);
      var
        reloc: TObjRelocation;
      begin
        reloc:=TObjRelocation.CreateSection(Size,aTarget,reltype);
        reloc.size:=len;
        ObjRelocations.Add(reloc);
        if reltype=RELOC_RELATIVE then
{ ARM does not require this adjustment, other CPUs must be checked }
{$if defined(i386) or defined(x86_64)}
          dec(offset,len)
{$endif i386 or x86_64}
        else if reltype<>RELOC_ABSOLUTE then
          InternalError(2012062401);
        if ElfTarget.relocs_use_addend then
          begin
            reloc.orgsize:=offset;
            offset:=0;
          end;
        write(offset,len);
      end;


{****************************************************************************
                            TElfObjData
****************************************************************************}

    constructor TElfObjData.create(const n:string);
      begin
        inherited create(n);
        CObjSection:=TElfObjSection;
      end;


    function TElfObjData.sectionname(atype:TAsmSectiontype;const aname:string;aorder:TAsmSectionOrder):string;
      const
        secnames : array[TAsmSectiontype] of string[length('__DATA, __datacoal_nt,coalesced')] = ('','',
          { TODO: sec_rodata is still writable }
          '.text','.data','.data','.rodata','.bss','.threadvar',
          '.pdata',
          '.text', { darwin stubs }
          '__DATA,__nl_symbol_ptr',
          '__DATA,__la_symbol_ptr',
          '__DATA,__mod_init_func',
          '__DATA,__mod_term_func',
          '.stab','.stabstr',
          '.idata$2','.idata$4','.idata$5','.idata$6','.idata$7','.edata',
          '.eh_frame',
          '.debug_frame','.debug_info','.debug_line','.debug_abbrev','.debug_aranges','.debug_ranges','.debug_loc','.debug_loclists',
          '.fpc',
          '.toc',
          '.init',
          '.fini',
          '.objc_class',
          '.objc_meta_class',
          '.objc_cat_cls_meth',
          '.objc_cat_inst_meth',
          '.objc_protocol',
          '.objc_string_object',
          '.objc_cls_meth',
          '.objc_inst_meth',
          '.objc_cls_refs',
          '.objc_message_refs',
          '.objc_symbols',
          '.objc_category',
          '.objc_class_vars',
          '.objc_instance_vars',
          '.objc_module_info',
          '.objc_class_names',
          '.objc_meth_var_types',
          '.objc_meth_var_names',
          '.objc_selector_strs',
          '.objc_protocol_ext',
          '.objc_class_ext',
          '.objc_property',
          '.objc_image_info',
          '.objc_cstring_object',
          '.objc_sel_fixup',
          '__DATA,__objc_data',
          '__DATA,__objc_const',
          '.objc_superrefs',
          '__DATA, __datacoal_nt,coalesced',
          '.objc_classlist',
          '.objc_nlclasslist',
          '.objc_catlist',
          '.obcj_nlcatlist',
          '.objc_protolist',
          '.stack',
          '.heap',
          '.gcc_except_table',
          '.ARM.attributes'
        );
      var
        sep : string[3];
        secname : string;
      begin
        { section type user gives the user full controll on the section name }
        if atype=sec_user then
          result:=aname
        else
          begin
            secname:=secnames[atype];
            if (atype=sec_fpc) and (Copy(aname,1,3)='res') then
              begin
                result:=secname+'.'+aname;
                exit;
              end;

            if atype=sec_threadvar then
              begin
                if (target_info.system in (systems_windows+systems_wince)) then
                  secname:='.tls'
                else if (target_info.system in systems_linux) then
                  secname:='.tbss';
              end;

            if create_smartlink_sections and (aname<>'') then
              begin
                case aorder of
                  secorder_begin :
                    sep:='.b_';
                  secorder_end :
                    sep:='.z_';
                  else
                    sep:='.n_';
                end;
                result:=secname+sep+aname
              end
            else
              result:=secname;
          end;
      end;


    procedure TElfObjData.CreateDebugSections;
      begin
        if target_dbg.id=dbg_stabs then
          begin
            stabssec:=createsection(sec_stab);
            stabstrsec:=createsection(sec_stabstr);
          end;
      end;


    procedure TElfObjData.writereloc(data:aint;len:aword;p:TObjSymbol;reltype:TObjRelocationType);
      type 
        multi = record
          case integer of
          0 : (ba : array[0..sizeof(aint)-1] of byte);
          1 : (b : byte);
          2 : (w : word);
          4 : (d : dword);
          8 : (q : qword);
        end;

      var
        symaddr : aint;
        ba : multi;
        b : byte;
        objreloc: TObjRelocation;
      begin
        if CurrObjSec=nil then
          internalerror(200403292);
        objreloc:=nil;
        if assigned(p) then
         begin
           { real address of the symbol }
           symaddr:=p.address;
           { Local ObjSymbols can be resolved already or need a section reloc }
           if (p.bind=AB_LOCAL) and
              (reltype in [RELOC_RELATIVE,RELOC_ABSOLUTE{$ifdef x86_64},RELOC_ABSOLUTE32{$endif x86_64}{$ifdef arm},RELOC_RELATIVE_24,RELOC_RELATIVE_CALL{$endif arm}]) then
             begin
{$ifdef ARM}
               if (reltype in [RELOC_RELATIVE_24,RELOC_RELATIVE_CALL]) and
                  (p.objsection=CurrObjSec) then
                 begin
                   data:=aint((data and $ff000000) or (((((data and $ffffff) shl 2)+(symaddr-CurrObjSec.Size)) shr 2) and $FFFFFF)); // TODO: Check overflow
                 end
               else
{$endif ARM}
               { For a reltype relocation in the same section the
                 value can be calculated }
               if (p.objsection=CurrObjSec) and
                  (reltype=RELOC_RELATIVE) then
                 inc(data,symaddr-len-CurrObjSec.Size)
               else
                 begin
                   objreloc:=TObjRelocation.CreateSection(CurrObjSec.Size,p.objsection,reltype);
                   CurrObjSec.ObjRelocations.Add(objreloc);
                   inc(data,symaddr);
                 end;
             end
           else
             begin
               objreloc:=TObjRelocation.CreateSymbol(CurrObjSec.Size,p,reltype);
               CurrObjSec.ObjRelocations.Add(objreloc);
               { If target is a local label and it isn't handled above,
                 patch its type in order to get it written to symtable.
                 This may happen e.g. when taking address of Pascal label in PIC mode. }
               if (p.bind=AB_LOCAL) and (p.typ=AT_LABEL) then
                 p.typ:=AT_ADDR;
            end;
         end;
        if assigned(objreloc) then
          begin
            objreloc.size:=len;
            { RELOC_GOTPCREL, RELOC_REX_GOTPCRELX, RELOC_GOTPCRELX] need special handling
              this is done in x86/aasmcpu unit }
            if reltype in [RELOC_RELATIVE{$ifdef x86},RELOC_PLT32{$endif}
               {$ifdef x86_64}, RELOC_GOTPCREL, RELOC_REX_GOTPCRELX, RELOC_GOTPCRELX,RELOC_TLSGD{$endif}] then
              dec(data,len);
            if ElfTarget.relocs_use_addend then
              begin
                objreloc.orgsize:=aword(data);
                data:=0;
              end;
          end;
        if target_info.endian<>source_info.endian then
          begin
            ba.q:=0;
            if (len<=sizeof(data)) then
              case len of
                1 : ba.b:=byte(data);
                2 : begin
                      ba.w:=word(data);
                      ba.w:=swapendian(ba.w);
                    end;
                4 : begin
                      ba.d:=dword(data);
                      ba.d:=swapendian(ba.d);
                    end;
                8 : begin
                      ba.q:=qword(data);
                      ba.q:=swapendian(ba.q);
                    end;
              else
                internalerror(2024012501);
              end;
            CurrObjSec.write(ba,len);
          end
        else
          CurrObjSec.write(data,len);
      end;


{****************************************************************************
                            TElfDynamicObjData
****************************************************************************}

    constructor TElfDynamicObjData.create(const n:string);
      begin
        inherited Create(n);
        FVersionDefs:=TFPHashObjectList.create(true);
        { Default symversions with indices 0 and 1 }
        TElfVersionDef.create(FVersionDefs,'*local*');
        TElfVersionDef.create(FVersionDefs,'*global*');
      end;


    destructor TElfDynamicObjData.destroy;
      begin
        FVersionDefs.free;
        inherited Destroy;
      end;


{****************************************************************************
                            TElfSymtab
****************************************************************************}

    const
      symsecnames: array[boolean] of string[8] = ('.symtab','.dynsym');
      strsecnames: array[boolean] of string[8] = ('.strtab','.dynstr');
      symsectypes: array[boolean] of longword  = (SHT_SYMTAB,SHT_DYNSYM);
      symsecattrs: array[boolean] of longword  = (0,SHF_ALLOC);


    constructor TElfSymtab.create(aObjData:TObjData;aKind:TElfSymtabKind);
      var
        dyn:boolean;
      begin
        dyn:=(aKind=esk_dyn);
        create_ext(aObjData,symsecnames[dyn],symsectypes[dyn],symsecattrs[dyn],sizeof(pint),sizeof(TElfSymbol));
        fstrsec:=TElfObjSection.create_ext(aObjData,strsecnames[dyn],SHT_STRTAB,symsecattrs[dyn],1,0);
        fstrsec.writezeros(1);
        writezeros(sizeof(TElfSymbol));
        symidx:=1;
        shinfo:=1;
        kind:=aKind;
      end;

    procedure TElfSymtab.writeInternalSymbol(avalue:aword;astridx:longword;ainfo:byte;ashndx:word);
      var
        elfsym:TElfSymbol;
      begin
        fillchar(elfsym,sizeof(elfsym),0);
        elfsym.st_value:=avalue;
        elfsym.st_name:=astridx;
        elfsym.st_info:=ainfo;
        elfsym.st_shndx:=ashndx;
        inc(symidx);
        inc(shinfo);
        MaybeSwapElfSymbol(elfsym);
        write(elfsym,sizeof(elfsym));
      end;

    procedure TElfSymtab.writeSymbol(objsym:TObjSymbol;nameidx:longword);
      var
        elfsym:TElfSymbol;
      begin
        fillchar(elfsym,sizeof(elfsym),0);
        if nameidx=0 then
          elfsym.st_name:=fstrsec.writestr(objsym.name)
        else
          elfsym.st_name:=nameidx;
        elfsym.st_size:=objsym.size;
        elfsym.st_value:=objsym.address;

{$ifdef ARM}
        if objsym.ThumbFunc then
          inc(elfsym.st_value);
{$endif ARM}
        { hidden symbols should have been converted to local symbols in
          the linking pass in case we're writing an exe/library; don't
          convert them to local here as well, as that would potentially
          hide a bug there. }
        case objsym.bind of
          AB_LOCAL :
            begin
              elfsym.st_info:=STB_LOCAL shl 4;
              inc(shinfo);
            end;
          AB_COMMON :
            begin
              elfsym.st_value:=size_2_align(objsym.size);
              elfsym.st_info:=STB_GLOBAL shl 4;
              elfsym.st_shndx:=SHN_COMMON;
            end;
          AB_EXTERNAL :
            elfsym.st_info:=STB_GLOBAL shl 4;
          AB_WEAK_EXTERNAL :
            elfsym.st_info:=STB_WEAK shl 4;
          AB_GLOBAL :
            elfsym.st_info:=STB_GLOBAL shl 4;
          AB_PRIVATE_EXTERN :
            begin
              elfsym.st_info:=STB_GLOBAL shl 4;
              SetElfSymbolVisibility(elfsym.st_other,STV_HIDDEN);
            end
        else
          InternalError(2012111801);
        end;
        { External symbols must be NOTYPE in relocatable files except if they are TLS symbols }
        if (objsym.bind<>AB_EXTERNAL) or (kind<>esk_obj) or (objsym.typ=AT_TLS) then
          begin
            case objsym.typ of
              AT_FUNCTION :
                elfsym.st_info:=elfsym.st_info or STT_FUNC;
              AT_DATA,
              AT_METADATA:
                elfsym.st_info:=elfsym.st_info or STT_OBJECT;
              AT_TLS:
                elfsym.st_info:=elfsym.st_info or STT_TLS;
              AT_GNU_IFUNC:
                elfsym.st_info:=elfsym.st_info or STT_GNU_IFUNC;
              { other types are implicitly mapped to STT_NOTYPE }
              else
                ;
            end;
          end;
        if objsym.bind<>AB_COMMON then
          begin
            if kind<>esk_obj then
              begin
                if assigned(objsym.objsection) and assigned(objsym.objsection.ExeSection) then
                  begin
                    if (objsym.typ=AT_TLS) then
                      elfsym.st_value:=elfsym.st_value-tlsbase
                    else if (oso_plt in objsym.objsection.SecOptions) then
                      elfsym.st_value:=0
                    else
                      elfsym.st_shndx:=TElfExeSection(objsym.objsection.ExeSection).secshidx;
                  end;
              end
            else
              begin
                if assigned(objsym.objsection) then
                  elfsym.st_shndx:=objsym.objsection.index
                else
                  elfsym.st_shndx:=SHN_UNDEF;
                objsym.symidx:=symidx;
              end;
          end;
        inc(symidx);
        MaybeSwapElfSymbol(elfsym);
        write(elfsym,sizeof(TElfSymbol));
      end;

{****************************************************************************
                            TElfObjectOutput
****************************************************************************}

    constructor TElfObjectOutput.create(AWriter:TObjectWriter);
      begin
        inherited Create(AWriter);
        CObjData:=TElfObjData;
      end;


    procedure TElfObjectOutput.createrelocsection(s:TElfObjSection;data:TObjData);
      var
        i    : longint;
        rel  : telfreloc;
        objreloc : TObjRelocation;
        relsym   : longint;
        relocsect : TElfObjSection;
      begin
        { create the reloc section }
        relocsect:=TElfObjSection.create_reloc(data,s.name,false);
        relocsect.shlink:=symtabsect.index;
        relocsect.shinfo:=s.index;
        { add the relocations }
        for i:=0 to s.Objrelocations.count-1 do
          begin
            objreloc:=TObjRelocation(s.Objrelocations[i]);

            { Symbol }
            if assigned(objreloc.symbol) then
              begin
                if objreloc.symbol.symidx=-1 then
                  begin
                    writeln(objreloc.symbol.Name);
                    internalerror(200603012);
                  end;
                relsym:=objreloc.symbol.symidx;
              end
            else
              begin
                if objreloc.objsection<>nil then
                  relsym:=objreloc.objsection.secsymidx
                else
                  relsym:=SHN_UNDEF;
              end;

            rel.address:=objreloc.dataoffset;
            rel.info:=ELF_R_INFO(relsym,ElfTarget.encodereloc(objreloc));
{$push}{$r-}
            rel.addend:=objreloc.orgsize;
{$pop}

            { write reloc }
            { ElfXX_Rel is essentially ElfXX_Rela without the addend field. }
            MaybeSwapElfReloc(rel);
            relocsect.write(rel,relocsect.shentsize);
          end;
      end;


    procedure TElfObjectOutput.section_write_symbol(p:TObject;arg:pointer);
      begin
        { Must not write symbols for internal sections like .symtab }
        { TODO: maybe use inclusive list of section types instead }
        if (TElfObjSection(p).shtype in [SHT_SYMTAB,SHT_STRTAB,SHT_REL,SHT_RELA]) then
          exit;
        TObjSection(p).secsymidx:=symtabsect.symidx;
        symtabsect.writeInternalSymbol(0,0,STT_SECTION,TObjSection(p).index);
      end;


    procedure TElfObjectOutput.createsymtab(data: TObjData);
      var
        i      : longint;
        objsym : TObjSymbol;
      begin
        with data do
         begin
           { section symbols }
           ObjSectionList.ForEachCall(@section_write_symbol,nil);
           { First the Local Symbols, this is required by ELF. The localsyms
             count stored in shinfo is used to skip the local symbols
             when traversing the symtab }
           for i:=0 to ObjSymbolList.Count-1 do
             begin
               objsym:=TObjSymbol(ObjSymbolList[i]);
               if (objsym.bind=AB_LOCAL) and (objsym.typ<>AT_LABEL) then
                 symtabsect.WriteSymbol(objsym);
             end;
           { Global Symbols }
           for i:=0 to ObjSymbolList.Count-1 do
             begin
               objsym:=TObjSymbol(ObjSymbolList[i]);
               if (objsym.bind<>AB_LOCAL) then
                 symtabsect.WriteSymbol(objsym);
             end;
           { update the .symtab section header }
           symtabsect.shlink:=symtabsect.fstrsec.index;
         end;
      end;


    procedure TElfObjectOutput.createshstrtab(data: TObjData);
      var
        i,prefixlen:longint;
        objsec,target:TElfObjSection;
      begin
        shstrtabsect.writezeros(1);
        prefixlen:=length('.rel')+ord(ElfTarget.relocs_use_addend);
        for i:=0 to data.ObjSectionList.Count-1 do
          begin
            objsec:=TElfObjSection(data.ObjSectionList[i]);
            { Alias section names into names of corresponding reloc sections,
              this is allowed by ELF specs and saves good half of .shstrtab space. }
            if objsec.shtype=relsec_shtype[ElfTarget.relocs_use_addend] then
              begin
                target:=TElfObjSection(data.ObjSectionList[objsec.shinfo-1]);
                if (target.ObjRelocations.Count=0) or
                   (target.shstridx<prefixlen) then
                  InternalError(2012101204);
                objsec.shstridx:=target.shstridx-prefixlen;
              end
            else
              begin
                if objsec.ObjRelocations.Count<>0 then
                  shstrtabsect.write(relsec_prefix[true][1],prefixlen);
                objsec.shstridx:=shstrtabsect.writestr(objsec.name);
              end;
          end;
      end;


    procedure TElfObjectOutput.writesectionheader(s:TElfObjSection);
      var
        sechdr : telfsechdr;
      begin
        fillchar(sechdr,sizeof(sechdr),0);
        sechdr.sh_name:=s.shstridx;
        sechdr.sh_type:=s.shtype;
        sechdr.sh_flags:=s.shflags;
        sechdr.sh_offset:=s.datapos;
        sechdr.sh_size:=s.Size;
        sechdr.sh_link:=s.shlink;
        sechdr.sh_info:=s.shinfo;
        sechdr.sh_addralign:=s.secalign;
        sechdr.sh_entsize:=s.shentsize;
        MaybeSwapSecHeader(sechdr);
        writer.write(sechdr,sizeof(sechdr));
      end;


    procedure TElfObjectOutput.section_count_sections(p:TObject;arg:pointer);
      begin
        TElfObjSection(p).index:=pword(arg)^;
        inc(pword(arg)^);
      end;


    procedure TElfObjectOutput.section_create_relocsec(p:TObject;arg:pointer);
      begin
        if (TElfObjSection(p).ObjRelocations.count>0) then
          createrelocsection(TElfObjSection(p),TObjData(arg));
      end;


    procedure TElfObjectOutput.section_write_sechdr(p:TObject;arg:pointer);
      begin
        writesectionheader(TElfObjSection(p));
      end;


    function TElfObjectOutput.writedata(data:TObjData):boolean;
      var
        header : telfheader;
        shoffset,
        datapos   : aword;
        nsections : word;
      begin
        result:=false;
        with data do
         begin
           { default sections }
           symtabsect:=TElfSymtab.create(data,esk_obj);
           shstrtabsect:=TElfObjSection.create_ext(data,'.shstrtab',SHT_STRTAB,0,1,0);
           { "no executable stack" marker }
           { TODO: used by OpenBSD/NetBSD as well? }
           if (target_info.system in (systems_linux + systems_android + systems_freebsd + systems_dragonfly)) and
              not(cs_executable_stack in current_settings.moduleswitches) then
             TElfObjSection.create_ext(data,'.note.GNU-stack',SHT_PROGBITS,0,1,0);
           { symbol for filename }
           symtabsect.fstrsec.writestr(ExtractFileName(current_module.mainsource));
           symtabsect.writeInternalSymbol(0,1,STT_FILE,SHN_ABS);
           { calc amount of sections we have }
           nsections:=1;
           { also create the index in the section header table }
           ObjSectionList.ForEachCall(@section_count_sections,@nsections);
           { create .symtab and .strtab }
           createsymtab(data);
           { Create the relocation sections, this needs valid secidx and symidx }
           ObjSectionList.ForEachCall(@section_create_relocsec,data);
           { recalc nsections to incude the reloc sections }
           nsections:=1;
           ObjSectionList.ForEachCall(@section_count_sections,@nsections);
           { create .shstrtab }
           createshstrtab(data);

           { Calculate the filepositions }
           datapos:=$40; { elfheader + alignment }
           { section data }
           layoutsections(datapos);
           { section headers }
           shoffset:=align(datapos,dword(Sizeof(AInt)));
           inc(datapos,(nsections+1)*sizeof(telfsechdr));

           { Write ELF Header }
           fillchar(header,sizeof(header),0);
           header.e_ident[EI_MAG0]:=ELFMAG0; { = #127'ELF' }
           header.e_ident[EI_MAG1]:=ELFMAG1;
           header.e_ident[EI_MAG2]:=ELFMAG2;
           header.e_ident[EI_MAG3]:=ELFMAG3;
           header.e_ident[EI_CLASS]:=ELFCLASS;
           if target_info.endian=endian_big then
             header.e_ident[EI_DATA]:=ELFDATA2MSB
           else
             header.e_ident[EI_DATA]:=ELFDATA2LSB;

           header.e_ident[EI_VERSION]:=1;
           if target_info.system in systems_openbsd then
             header.e_ident[EI_OSABI]:=ELFOSABI_OPENBSD
           else if target_info.system in systems_freebsd then
             header.e_ident[EI_OSABI]:=ELFOSABI_FREEBSD
           else if target_info.system in systems_dragonfly then
             header.e_ident[EI_OSABI]:=ELFOSABI_NONE;
           header.e_type:=ET_REL;
           header.e_machine:=ElfTarget.machine_code;
           header.e_version:=1;
           header.e_shoff:=shoffset;
           header.e_shstrndx:=shstrtabsect.index;

           header.e_shnum:=nsections;
           header.e_ehsize:=sizeof(telfheader);
           header.e_shentsize:=sizeof(telfsechdr);
           if assigned(ElfTarget.encodeflags) then
             header.e_flags:=ElfTarget.encodeflags();
           MaybeSwapHeader(header);
           writer.write(header,sizeof(header));
           writer.writezeros($40-sizeof(header)); { align }
           { Sections }
           WriteSectionContent(data);

           { Align header }
           Writer.Writezeros(Align(Writer.Size,Sizeof(AInt))-Writer.Size);
           { section headers, start with an empty header for sh_undef }
           writer.writezeros(sizeof(telfsechdr));
           ObjSectionList.ForEachCall(@section_write_sechdr,nil);
         end;
        result:=true;
      end;


{****************************************************************************
                               TELFAssembler
****************************************************************************}

    constructor TElfAssembler.Create(info: pasminfo; smart:boolean);
      begin
        inherited;
        CObjOutput:=TElfObjectOutput;
        CInternalAr:=tarobjectwriter;
      end;


{****************************************************************************
                               TELFObjectInput
****************************************************************************}

    constructor TElfObjInput.Create;
      begin
        inherited Create;
        CObjData:=TElfObjData;
        CObjSymbol:=TObjSymbol;
      end;


    destructor TElfObjInput.Destroy;
      begin
        if Assigned(FSymTbl) then
          FreeMem(FSymTbl);
        if Assigned(FSecTbl) then
          FreeMem(FSecTbl);
        if Assigned(strtab) then
          FreeMem(strtab);
        if Assigned(shstrtab) then
          FreeMem(shstrtab);
        if Assigned(symversions) then
          FreeMem(symversions);
        inherited Destroy;
      end;


    procedure TElfObjInput.LoadRelocations(const secrec:TSectionRec);
      var
        i: longint;
        rel: TElfReloc;
        reltyp: byte;
        relsym: longint;
        objrel: TObjRelocation;
        p: TObjSymbol;
      begin
        FReader.Seek(secrec.relocpos);
        if secrec.sec=nil then
          InternalError(2012060203);
        if (secrec.relentsize=3*sizeof(pint)) then
          with secrec.sec do SecOptions:=SecOptions+[oso_rela_relocs];
        for i:=0 to secrec.relocs-1 do
          begin
            FReader.Read(rel,secrec.relentsize);
            MaybeSwapElfReloc(rel);
            reltyp:=rel.info and $FF;
{$ifdef cpu64bitaddr}
            relsym:=rel.info shr 32;
{$else cpu64bitaddr}
            relsym:=(rel.info shr 8) and $FFFFFF;
{$endif cpu64bitaddr}
            if relsym>=syms then
              InternalError(2012060204);
            p:=TObjSymbol(FSymTbl[relsym]);
            { Some relocations (e.g. R_ARM_V4BX) don't use a symbol at all }
            if assigned(p) or (relsym=0) then
              begin
                objrel:=TObjRelocation.CreateRaw(rel.address-secrec.sec.mempos,p,reltyp);
                if (secrec.relentsize=3*sizeof(pint)) then
                  objrel.orgsize:=rel.addend;
                { perform target-specific actions }
                if Assigned(ElfTarget.loadreloc) then
                  ElfTarget.loadreloc(objrel);
                secrec.sec.ObjRelocations.add(objrel);
              end
            else
              begin
                InputError('Unable to resolve symbol of relocation');
                exit;
              end;
          end;
      end;


    procedure TElfObjInput.LoadSymbols(objdata:TObjData;count,locals:longword);
      var
        i: longint;
        sym: TElfSymbol;
        bind: TAsmSymBind;
        typ: TAsmSymType;
        objsym: TObjSymbol;
        ver: word;
      begin
        FSymTbl:=AllocMem(count*sizeof(Pointer));
        for i:=1 to count-1 do
          begin
            FReader.Read(sym,sizeof(TElfSymbol));
            MaybeSwapElfSymbol(sym);
            if sym.st_name>=strtablen then
              InternalError(2012060205);

            if sym.st_shndx=SHN_ABS then    { ignore absolute symbols (should we really do it???) }
              Continue
            else if sym.st_shndx=SHN_COMMON then
              bind:=AB_COMMON
            else if (sym.st_shndx>=nsects) then
              InternalError(2012060206)
            else
              case (sym.st_info shr 4) of
                STB_LOCAL:
                  bind:=AB_LOCAL;
                STB_GLOBAL:
                  if sym.st_shndx=SHN_UNDEF then
                    bind:=AB_EXTERNAL
                  else if GetElfSymbolVisibility(sym.st_other)=STV_HIDDEN then
                    bind:=AB_PRIVATE_EXTERN
                  else
                    bind:=AB_GLOBAL;
                STB_WEAK:
                  bind:=AB_WEAK_EXTERNAL;
              else
                InternalError(2012060207);
              end;

            { Ignore section symbol if we didn't create the corresponding objsection
              (examples are SHT_GROUP or .note.GNU-stack sections). }
            if (sym.st_shndx>0) and (sym.st_shndx<SHN_LORESERVE) and
              (FSecTbl[sym.st_shndx].sec=nil) and
              (not dynobj) then
              if ((sym.st_info and $0F)=STT_SECTION) then
                Continue
              else
                begin
                  writeln(objdata.name,' ',i);
                  InternalError(2012110701)
                end;

            case (sym.st_info and $0F) of
              STT_NOTYPE:
                typ:=AT_NONE;
              STT_OBJECT:
                typ:=AT_DATA;
              STT_FUNC:
                typ:=AT_FUNCTION;
              STT_SECTION:
                typ:=AT_SECTION;
              STT_FILE:
                continue;
              STT_TLS:
                typ:=AT_TLS;
              STT_GNU_IFUNC:
                typ:=AT_GNU_IFUNC;
            else
              writeln(objdata.name,' ',sym.st_info and $0F);
              InternalError(2012060208);
            end;
            { If reading DSO, we're interested only in global symbols defined there.
              Symbols with non-current version should also be ignored. }
            ver:=0;
            if dynobj then
              begin
                if assigned(symversions) then
                  begin
                    ver:=symversions[i];
                    if (ver=VER_NDX_LOCAL) or (ver>VERSYM_VERSION) then
                      continue;
                  end;
                if (bind=AB_LOCAL) or (sym.st_shndx=SHN_UNDEF) then
                  continue;
                if ver>=verdefs.count then
                  InternalError(2012120505);
              end;
            { validity of name and objsection has been checked above }
            { !! all AT_SECTION symbols have duplicate (null) name,
              therefore TObjSection.CreateSymbol cannot be used here }
            objsym:=CObjSymbol.Create(objdata.ObjSymbolList,string(PChar(@strtab[sym.st_name])));
            objsym.bind:=bind;
            objsym.typ:=typ;
            if bind<>AB_COMMON then
              objsym.objsection:=FSecTbl[sym.st_shndx].sec;
            objsym.offset:=sym.st_value;
            objsym.size:=sym.st_size;
            FSymTbl[i]:=objsym;
            if (ver>VER_NDX_GLOBAL) then
              TVersionedObjSymbol(objsym).version:=TElfVersionDef(verdefs[ver]);
          end;
      end;


    function TElfObjInput.CreateSection(const shdr:TElfsechdr;index:longint;objdata:tobjdata;
        out secname:string):TElfObjSection;
      begin
        secname:=string(PChar(@shstrtab[shdr.sh_name]));

        result:=TElfObjSection.create_ext(objdata,secname,
          shdr.sh_type,shdr.sh_flags,shdr.sh_addralign,shdr.sh_entsize);

        result.index:=index;
        result.DataPos:=shdr.sh_offset;
        result.MemPos:=shdr.sh_addr;
        result.Size:=shdr.sh_size;
        FSecTbl[index].sec:=result;
      end;


    function TElfObjInput.ReadBytes(offs:longint;out buf;len:longint):boolean;
      begin
        FReader.Seek(offs);
        result:=FReader.Read(buf,len);
      end;


    procedure TElfObjInput.LoadSection(const shdr:TElfsechdr;index:longint;objdata:tobjdata);
      var
        sec: TElfObjSection;
        sym: TElfSymbol;
        secname: string;
      begin
        if shdr.sh_name>=shstrtablen then
          InternalError(2012060210);

        case shdr.sh_type of
          SHT_NULL:
            {ignore};

          { SHT_STRTAB may appear for .stabstr and other debug sections.
            .shstrtab and .strtab are processed separately and don't appear here. }
          SHT_PROGBITS,SHT_NOBITS,SHT_NOTE,SHT_STRTAB,
          SHT_INIT_ARRAY,SHT_FINI_ARRAY,SHT_PREINIT_ARRAY:
            begin
              sec:=CreateSection(shdr,index,objdata,secname);

              if (Length(secname)>3) and (secname[2] in ['d','f','n','s']) then
                begin
                  if (Pos('.stub',secname)=1) or
                    (Pos('.fpc',secname)=1) then
                    sec.SecOptions:=[oso_keep]
                  { ELF does not have any flags specific to debug sections,
                    but reserves names starting with '.debug' for this purpose }
                  else if (Pos('.debug',secname)=1) or
                    (secname='.stab') or
                    (secname='.stabstr') then
                    sec.SecOptions:=[oso_debug]
                  else if (secname='.note.GNU-stack') and (shdr.sh_type=SHT_PROGBITS) then
                    begin
                      if (shdr.sh_flags and SHF_EXECINSTR)=0 then
                        objdata.ExecStack:=False;
                    end;
                end;

              if (shdr.sh_type=SHT_NOTE) and (shdr.sh_size<>0) then
                sec.SecOptions:=[oso_keep];
            end;

          SHT_REL,SHT_RELA:
            begin
              if shdr.sh_info>=nsects then
                InternalError(2012060211);
              if shdr.sh_entsize<>longword((2+ord(shdr.sh_type=SHT_RELA))*sizeof(pint)) then
                InternalError(2012060212);

              with FSecTbl[shdr.sh_info] do
                begin
                  relocpos:=shdr.sh_offset;
                  relocs:=shdr.sh_size div shdr.sh_entsize;
                  relentsize:=shdr.sh_entsize;
                end;
            end;

          SHT_GROUP:
            if (shdr.sh_size>=2*sizeof(longword)) and
              (shdr.sh_entsize=sizeof(longword)) and
              ((shdr.sh_size mod shdr.sh_entsize)=0) then
              begin
                { Groups are identified by name of symbol pointed to by
                  sh_link and sh_info, not by sh_name. This symbol
                  may as well be STT_SECTION symbol of this section,
                  in which case we end up using sh_name. }
                if dynobj then
                  InternalError(2012110801);
                if (shdr.sh_link<>symtabndx) then
                  InternalError(2012110703);
                if (shdr.sh_info>=syms) then
                  InternalError(2012110704);

                FReader.Seek(symtaboffset+shdr.sh_info*sizeof(TElfSymbol));
                FReader.Read(sym,sizeof(TElfSymbol));
                MaybeSwapElfSymbol(sym);
                if sym.st_name>=strtablen then
                  InternalError(2012110705);
                if (sym.st_shndx=index) and (sym.st_info=((STB_LOCAL shl 4) or STT_SECTION)) then
                  secname:=string(PChar(@shstrtab[shdr.sh_name]))
                else
                  secname:=string(PChar(@strtab[sym.st_name]));

                { Postpone further processing until all sections are loaded,
                  we'll need to access correct section header.
                  Since ABI requires SHT_GROUP sections to come first in the file,
                  we assume that group number x has header index x+1.
                  If we ever encounter files where this is not true, we'll have
                  to maintain a separate index. }
                objdata.CreateSectionGroup(secname);
                if (index<>objdata.GroupsList.Count) then
                  InternalError(2012110802);
              end
            else
              InternalError(2012110706);

          SHT_GNU_ATTRIBUTES:
            { TODO: must not be ignored };
        else
          if not (assigned(ElfTarget.loadsection) and
            ElfTarget.loadsection(self,objdata,shdr,index)) then
            InternalError(2012072603);
        end;
        FLoaded[index]:=True;
      end;


    function TElfObjInput.LoadHeader(out objdata:TObjData):boolean;
      var
        header:TElfHeader;
      begin
        result:=false;
        if not FReader.read(header,sizeof(header)) then
          begin
            InputError('Can''t read ELF header');
            exit;
          end;
        if (header.e_ident[EI_MAG0]<>ELFMAG0) or (header.e_ident[EI_MAG1]<>ELFMAG1) or
           (header.e_ident[EI_MAG2]<>ELFMAG2) or (header.e_ident[EI_MAG3]<>ELFMAG3) then
          begin
            InputError('Illegal ELF magic');
            exit;
          end;
        if (header.e_ident[EI_VERSION]<>1) then
          begin
            InputError('Unknown ELF file version');
            exit;
          end;
        if (header.e_ident[EI_CLASS]<>ELFCLASS) then
          begin
            InputError('Wrong ELF file class (32/64 bit mismatch)');
            exit;
          end;
        if (header.e_ident[EI_DATA]<>1+ord(target_info.endian=endian_big)) then
          begin
            InputError('ELF endianness does not match target');
            exit;
          end;
        MaybeSwapHeader(header);
        if (header.e_version<>1) then
          begin
            InputError('Unknown ELF data version');
            exit;
          end;
        if (header.e_machine<>ElfTarget.machine_code) then
          begin
            InputError('ELF file is for different CPU');
            exit;
          end;
        if (header.e_type<>ET_REL) and (header.e_type<>ET_DYN) then
          begin
            InputError('Not a relocatable or dynamic ELF file');
            exit;
          end;
        if header.e_shentsize<>sizeof(TElfsechdr) then
          InternalError(2012062701);

        nsects:=header.e_shnum;
        dynobj:=(header.e_type=ET_DYN);
        shoffset:=header.e_shoff;
        shstrndx:=header.e_shstrndx;

        if dynobj then
          begin
            objdata:=TElfDynamicObjData.Create(InputFilename);
            verdefs:=TElfDynamicObjData(objdata).versiondefs;
            CObjSymbol:=TVersionedObjSymbol;
          end
        else
          objdata:=CObjData.Create(InputFilename);

        TElfObjData(objdata).ident:=header.e_ident;
        TElfObjData(objdata).flags:=header.e_flags;
        result:=true;
      end;


    procedure TElfObjInput.LoadDynamic(const shdr:TElfsechdr;objdata:TObjData);
      var
        dt: TElfDyn;
        i: longint;
      begin
        if (shdr.sh_entsize<>sizeof(TElfDyn)) then
          InternalError(2012071403);

        FReader.Seek(shdr.sh_offset);
        for i:=0 to (shdr.sh_size div shdr.sh_entsize)-1 do
          begin
            FReader.Read(dt,sizeof(TElfDyn));
            MaybeSwapElfDyn(dt);
            case dt.d_tag of
              DT_NULL:
                break;
              DT_SONAME:
                TElfObjData(objdata).FName:=string(PChar(@strtab[dt.d_ptr]));
              DT_NEEDED:
                ;
            end;
          end;
      end;


    function TElfObjInput.ReadObjData(AReader:TObjectreader;out objdata:TObjData):boolean;
      var
        i,j,strndx,dynndx,
        versymndx,verdefndx,verneedndx: longint;
        objsec: TObjSection;
        grp: TObjSectionGroup;
        tmp: longword;
        count: longint;
        vd: TElfverdef;
        vda: TElfverdaux;
        vdoffset: aword;
      begin
        FReader:=AReader;
        InputFileName:=AReader.FileName;
        result:=false;
        strndx:=0;

        if not LoadHeader(objData) then
          exit;

        FSecTbl:=AllocMem(nsects*sizeof(TSectionRec));
        FLoaded:=AllocMem(nsects*sizeof(boolean));
        SetLength(shdrs,nsects);

        FReader.Seek(shoffset);
        if not FReader.Read(shdrs[0],nsects*sizeof(TElfsechdr)) then
          begin
            InputError('Can''t read ELF section headers');
            exit;
          end;
        if source_info.endian<>target_info.endian then
          for i:=0 to nsects-1 do
            MaybeSwapSecHeader(shdrs[i]);

        { First, load the .shstrtab section }
        if shstrndx>=nsects then
          InternalError(2012060201);
        if shdrs[shstrndx].sh_type<>SHT_STRTAB then
          InternalError(2012060202);
        shstrtablen:=shdrs[shstrndx].sh_size;
        GetMem(shstrtab,shstrtablen);
        FReader.seek(shdrs[shstrndx].sh_offset);
        FReader.read(shstrtab^,shstrtablen);
        FLoaded[shstrndx]:=True;

        { Locate the symtable, it is typically at the end so loop backwards.
          Load the strings, postpone symtable itself until done with sections.
          Note that is is legal to have no symtable.
          For DSO, locate .dynsym instead, this one is near the beginning, but
          overall number of sections won't be big. }
        symtabndx:=0;
        for i:=nsects-1 downto 1 do
          begin
            if (shdrs[i].sh_type<>symsectypes[dynobj]) then
              continue;
            if (shdrs[i].sh_entsize<>sizeof(TElfSymbol)) then
              InternalError(2012060213);
            if shdrs[i].sh_link>=nsects then
              InternalError(2012062702);
            strndx:=shdrs[i].sh_link;
            if shdrs[strndx].sh_type<>SHT_STRTAB then
              InternalError(2012062703);
            strtablen:=shdrs[strndx].sh_size;
            GetMem(strtab,strtablen);
            FReader.seek(shdrs[strndx].sh_offset);
            FReader.read(strtab^,strtablen);

            symtaboffset:=shdrs[i].sh_offset;
            syms:=shdrs[i].sh_size div sizeof(TElfSymbol);
            localsyms:=shdrs[i].sh_info;
            FLoaded[i]:=True;
            FLoaded[strndx]:=True;
            symtabndx:=i;
            break;
          end;

        if dynobj then
          begin
            if symtabndx=0 then
              InternalError(2012110707);
            { Locate .dynamic and version sections. Expect a single one of a kind. }
            dynndx:=0;
            versymndx:=0;
            verdefndx:=0;
            verneedndx:=0;
            for i:=nsects-1 downto 0 do
              begin
                case shdrs[i].sh_type of
                  SHT_DYNAMIC:
                    begin
                      if dynndx<>0 then
                        InternalError(2012102001);
                      dynndx:=i;
                      if (shdrs[dynndx].sh_link<>strndx) then
                        InternalError(2012071402);
                      LoadDynamic(shdrs[dynndx],objdata);
                    end;

                  SHT_GNU_versym:
                    begin
                      if versymndx<>0 then
                        InternalError(2012102002);
                      versymndx:=i;
                      if shdrs[i].sh_entsize<>sizeof(word) then
                        InternalError(2012102003);
                      if shdrs[i].sh_link<>symtabndx then
                        InternalError(2012102004);
                      if shdrs[i].sh_size<>syms*sizeof(word) then
                        InternalError(2012102005);
                      GetMem(symversions,shdrs[i].sh_size);
                      FReader.seek(shdrs[i].sh_offset);
                      FReader.read(symversions^,shdrs[i].sh_size);
                      if source_info.endian<>target_info.endian then
                        for j:=0 to syms-1 do
                          symversions[j]:=SwapEndian(symversions[j]);
                    end;

                  SHT_GNU_verdef:
                    begin
                      if verdefndx<>0 then
                        InternalError(2012102006);
                      verdefndx:=i;
                      if shdrs[i].sh_link<>strndx then
                        InternalError(2012120501);
                      vdoffset:=shdrs[i].sh_offset;
                      { TODO: can we rely on sh_info, or must read until vd_next=0? }
                      for j:=1 to shdrs[i].sh_info do
                        begin
                          FReader.seek(vdoffset);
                          FReader.Read(vd,sizeof(TElfverdef));
                          MaybeSwapElfverdef(vd);
                          if vd.vd_version<>VER_DEF_CURRENT then
                            InternalError(2012120502);
                          FReader.seek(vdoffset+vd.vd_aux);
                          vdoffset:=vdoffset+vd.vd_next;
                          { First verdaux entry holds name of version (unless VER_FLG_BASE flag is set),
                            subsequent one(s) point to parent(s). For our purposes, version hierarchy
                            looks irrelevant. }
                          FReader.Read(vda,sizeof(TElfverdaux));
                          MaybeSwapElfverdaux(vda);
                          if vda.vda_name>=strtablen then
                            InternalError(2012120503);
                          if (vd.vd_flags and VER_FLG_BASE)<>0 then
                            continue;
                          { Assuming verdef indices assigned continuously starting from 2,
                            at least BFD produces files that way. }
                          if verdefs.count<>vd.vd_ndx then
                            InternalError(2012120504);
                          TElfVersionDef.Create(verdefs,string(PChar(@strtab[vda.vda_name])));
                        end;
                    end;

                  SHT_GNU_verneed:
                    begin
                      if verneedndx<>0 then
                        InternalError(2012102007);
                      verneedndx:=i;
                      //sh_link->.dynstr
                      //sh_info->number of entries
                    end;
                end;
             end;

            if dynndx=0 then
              InternalError(2012071401);

            { load the symtable }
            FReader.Seek(symtaboffset+sizeof(TElfSymbol));
            LoadSymbols(objdata,syms,localsyms);

            result:=True;
            exit;
          end;

        { assume stack is executable until proven otherwise }
        objdata.ExecStack:=True;

        { Process section headers }
        for i:=1 to nsects-1 do
          if not FLoaded[i] then
            LoadSection(shdrs[i],i,objdata);

        { load the content }
        ReadSectionContent(objdata);

        { load the symtable }
        FReader.Seek(symtaboffset+sizeof(TElfSymbol));
        LoadSymbols(objdata,syms,localsyms);

        { finish relocations }
        for i:=0 to objdata.ObjSectionList.Count-1 do
          begin
            objsec:=TObjSection(objdata.ObjsectionList[i]);
            { skip debug sections }
            if (oso_debug in objsec.SecOptions) and
               (cs_link_strip in current_settings.globalswitches) and
               not(cs_link_separate_dbg_file in current_settings.globalswitches) then
              continue;

            if FSecTbl[objsec.index].relocpos>0 then
              LoadRelocations(FSecTbl[objsec.index]);
          end;

        { finish processing section groups, if any }
        if Assigned(objdata.GroupsList) then
          begin
            for i:=0 to objdata.GroupsList.Count-1 do
              begin
                grp:=TObjSectionGroup(objData.GroupsList[i]);
                FReader.Seek(shdrs[i+1].sh_offset);
                { first dword is flags }
                FReader.Read(tmp,sizeof(longword));
                if source_info.endian<>target_info.endian then
                  tmp:=SwapEndian(tmp);
                if (tmp and GRP_COMDAT)<>0 then
                  grp.IsComdat:=true;

                count:=(shdrs[i+1].sh_size div sizeof(longword))-1;
                SetLength(grp.members,count);
                for j:=0 to count-1 do
                  begin
                    FReader.Read(tmp,sizeof(longword));
                    if source_info.endian<>target_info.endian then
                      tmp:=SwapEndian(tmp);
                    if (tmp>=nsects) then
                      InternalError(2012110805);
                    objsec:=FSecTbl[tmp].sec;
                    if (objsec=nil) then
                      InternalError(2012110806);
                    if (TElfObjSection(objsec).shflags and SHF_GROUP)=0 then
                      InternalError(2012110807);
                    grp.members[j]:=objsec;
                    objsec.Group:=grp;
                  end;
              end;
          end;

        result:=True;
      end;


    class function TElfObjInput.CanReadObjData(AReader:TObjectreader):boolean;
      var
        header: TElfHeader;
      begin
        result:=false;
        if AReader.Read(header,sizeof(header)) then
          begin;
            if (header.e_ident[EI_MAG0]=ELFMAG0) and (header.e_ident[EI_MAG1]=ELFMAG1) and
               (header.e_ident[EI_MAG2]=ELFMAG2) and (header.e_ident[EI_MAG3]=ELFMAG3) then
            { TODO: check additional fields }
              result:=true;
          end;
        AReader.Seek(0);
      end;

{*****************************************************************************
                                  TElfExeOutput
*****************************************************************************}

    constructor TElfExeOutput.Create;
      begin
        inherited Create;
        CObjData:=TElfObjData;
        CExeSection:=TElfExeSection;
{$ifdef cpu64}
        MaxMemPos:=Qword($FFFFFFFFFFFFFFFF);
        //MaxMemPos:=$7EFFFFFF;   { As specified by SysV AMD64 ABI for small memory model }
{$else cpu64}
        MaxMemPos:=$7FFFFFFF;
{$endif cpu64}
        SectionMemAlign:=$20;
        SectionDataAlign:=$20;
        segmentlist:=TFPObjectList.Create(True);
        neededlist:=TFPHashList.Create;
      end;


    destructor TElfExeOutput.Destroy;
      begin
        dyncopysyms.Free;
        neededlist.Free;
        segmentlist.Free;
        dynsymlist.Free;
        dynreloclist.Free;
        if assigned(dynsymnames) then
          FreeMem(dynsymnames);
        stringdispose(FInterpreter);
        inherited Destroy;
      end;


    function TElfExeOutput.AttachSection(objsec:TObjSection):TElfExeSection;
      begin
        objsec.SecOptions:=[oso_keep];
        result:=TElfExeSection(FindExeSection(objsec.name));
        if result=nil then
          result:=TElfExeSection.Create(ExeSectionList,objsec.name);
        result.AddObjSection(objsec);
      end;


    function TElfExeOutput.CreateSegment(atype,aflags,aalign:longword):TElfSegment;
      begin
        result:=TElfSegment.Create(atype,aflags,aalign);
        segmentlist.add(result);
      end;


    procedure TElfExeOutput.WriteHeader;
      var
        header: TElfHeader;
      begin
        FillChar(header,sizeof(header),0);
        header.e_ident[EI_MAG0]:=ELFMAG0; { = #127'ELF' }
        header.e_ident[EI_MAG1]:=ELFMAG1;
        header.e_ident[EI_MAG2]:=ELFMAG2;
        header.e_ident[EI_MAG3]:=ELFMAG3;
        header.e_ident[EI_CLASS]:=ELFCLASS;
        if target_info.endian=endian_big then
          header.e_ident[EI_DATA]:=ELFDATA2MSB
        else
          header.e_ident[EI_DATA]:=ELFDATA2LSB;

        header.e_ident[EI_VERSION]:=1;
        if target_info.system in systems_openbsd then
          header.e_ident[EI_OSABI]:=ELFOSABI_OPENBSD
        else if target_info.system in systems_freebsd then
          header.e_ident[EI_OSABI]:=ELFOSABI_FREEBSD
        else if target_info.system in systems_dragonfly then
          header.e_ident[EI_OSABI]:=ELFOSABI_NONE;
        if IsSharedLibrary then
          header.e_type:=ET_DYN
        else
          header.e_type:=ET_EXEC;
        header.e_machine:=ElfTarget.machine_code;
        header.e_version:=1;
        header.e_phoff:=sizeof(TElfHeader);
        header.e_shoff:=shoffset;
        header.e_shstrndx:=ExeSectionList.IndexOf(shstrtabsect.ExeSection)+1;

        header.e_shnum:=ExeSectionList.Count+1;
        header.e_phnum:=segmentlist.count;
        header.e_ehsize:=sizeof(telfheader);
        if assigned(ElfTarget.encodeflags) then
          header.e_flags:=ElfTarget.encodeflags();
        if assigned(EntrySym) then
          header.e_entry:=EntrySym.Address;
        header.e_shentsize:=sizeof(telfsechdr);
        header.e_phentsize:=sizeof(telfproghdr);
        MaybeSwapHeader(header);
        FWriter.Write(header,sizeof(header));
      end;


    procedure TElfExeOutput.exesection_write_header(p:TObject;arg:Pointer);
      var
        shdr: TElfsechdr;
        exesec: TElfExeSection absolute p;
      begin
        FillChar(shdr,sizeof(shdr),0);
        shdr.sh_name:=exesec.shstridx;
        if (ExeWriteMode=ewm_dbgonly) and
           (exesec.SecOptions*[oso_debug,oso_debug_copy]=[]) then
          shdr.sh_type:=SHT_NOBITS
        else
          shdr.sh_type:=exesec.shtype;
        shdr.sh_flags:=exesec.shflags;
        if (oso_load in exesec.SecOptions) then
          shdr.sh_addr:=exesec.MemPos;
        shdr.sh_offset:=exesec.DataPos;
        shdr.sh_size:=exesec.Size;
        shdr.sh_link:=exesec.shlink;
        shdr.sh_info:=exesec.shinfo;
        shdr.sh_addralign:=exesec.SecAlign;
        shdr.sh_entsize:=exesec.shentsize;
        MaybeSwapSecHeader(shdr);
        FWriter.Write(shdr,sizeof(shdr));
      end;


    procedure TElfExeOutput.segment_write_header(p:TObject;arg:Pointer);
      var
        phdr: TElfproghdr;
        seg: TElfSegment absolute p;
      begin
        FillChar(phdr,sizeof(phdr),0);
        phdr.p_type:=seg.ptype;
        phdr.p_flags:=seg.pflags;
        phdr.p_align:=seg.align;
        phdr.p_offset:=seg.DataPos;
        phdr.p_filesz:=seg.DataSize;
        phdr.p_memsz:=seg.MemSize;
        phdr.p_vaddr:=seg.MemPos;
        phdr.p_paddr:=seg.MemPos;

        MaybeSwapHeader(phdr);
        FWriter.Write(phdr,sizeof(phdr));
      end;


    procedure TElfExeOutput.WriteStaticSymtable;
      var
        i: longint;
        sec: TElfExeSection;
        exesym: TExeSymbol;
      begin
        if assigned(tlsseg) then
          symtab.tlsbase:=tlsseg.MemPos;
        for i:=0 to ExeSectionList.Count-1 do
          begin
            sec:=TElfExeSection(ExeSectionList[i]);
            { Must not write symbols for internal sections like .symtab }
            if (sec.shtype in [SHT_SYMTAB,SHT_STRTAB,SHT_REL,SHT_RELA]) then
              continue;
            sec.secsymidx:=symtab.symidx;
            symtab.writeInternalSymbol(sec.mempos,0,STT_SECTION,sec.secshidx);
          end;
        { local symbols first }
        for i:=0 to ExeSymbolList.Count-1 do
          begin
            exesym:=TExeSymbol(ExeSymbolList[i]);
            if (exesym.objsymbol.bind=AB_LOCAL) and (exesym.objsymbol.typ<>AT_LABEL) then
              symtab.WriteSymbol(exesym.objsymbol);
          end;
        { Global Symbols }
        for i:=0 to ExeSymbolList.Count-1 do
          begin
            exesym:=TExeSymbol(ExeSymbolList[i]);
            if (exesym.objsymbol.bind<>AB_LOCAL) then
              symtab.WriteSymbol(exesym.objsymbol);
          end;
        { update exe section properties }
        symtab.ExeSection.size:=symtab.size;
        TElfExeSection(symtab.ExeSection).shinfo:=symtab.shinfo;
        TElfExeSection(symtab.ExeSection).shlink:=ExeSectionList.IndexOf(symtab.fstrsec.ExeSection)+1;
        symtab.fstrsec.ExeSection.Size:=symtab.fstrsec.size;
      end;


    procedure TElfExeOutput.MapSectionsToSegments;
      var
        seg: TElfSegment;
        exesec: TExeSection;
        i: longint;
      begin
        if (not IsSharedLibrary) and assigned(interpobjsec) then
          begin
            phdrseg:=CreateSegment(PT_PHDR,PF_R or PF_X,sizeof(pint));
            seg:=CreateSegment(PT_INTERP,PF_R,1);
            seg.Add(interpobjsec.ExeSection);
          end;

        textseg:=CreateSegment(PT_LOAD,PF_X or PF_R,ElfTarget.max_page_size);
        dataseg:=CreateSegment(PT_LOAD,PF_R or PF_W,ElfTarget.max_page_size);
        for i:=0 to ExeSectionList.Count-1 do
          begin
            exesec:=TExeSection(ExeSectionList[i]);
            if (oso_load in exesec.SecOptions) then
              begin
                if (TElfExeSection(exesec).shflags and SHF_TLS)<>0 then
                  begin
                    if tlsseg=nil then
                      tlsseg:=CreateSegment(PT_TLS,PF_R,sizeof(pint));
                    tlsseg.add(exesec);
                  end;

                { TODO: at least on Linux, ld seems to drop .note.ABI-tag for static executables.
                  (Logic is as follows: there is no .note.ABI-tag section in ld script, so it
                  is processed as orphan section. As such, it is placed after .interp.
                  For static executables .interp is dropped, and it looks like there's nowhere to
                  place .note.ABI-tag in this case)
                  Always including it doesn't harm though (except increasing file size). }
                if TElfExeSection(exesec).shtype=SHT_NOTE then
                  begin
                    if noteseg=nil then
                      noteseg:=CreateSegment(PT_NOTE,PF_R,4);
                    noteseg.Add(exesec);
                    Include(exesec.SecOptions,oso_debug_copy);
                  end;
                if (oso_executable in exesec.SecOptions) or
                  not (oso_write in exesec.SecOptions) then
                  textseg.add(exesec)
                else
                  dataseg.add(exesec);
              end;
          end;

        if dynamiclink then
          begin
            seg:=CreateSegment(PT_DYNAMIC,PF_R or PF_W,sizeof(pint));
            seg.add(dynamicsec.ExeSection);
          end;

        { stack flags }
        CreateSegment(PT_GNU_STACK,PF_R or PF_W or (PF_X*ord(ExecStack)),sizeof(pint));
      end;


    procedure TElfExeOutput.make_dynamic_if_undefweak(exesym:TExeSymbol);
      begin
        if (exesym.dynindex=0) and (exesym.state=symstate_undefweak) and
          not (cs_link_staticflag in current_settings.globalswitches) then
          exesym.dynindex:=dynsymlist.add(exesym)+1;
      end;


    function TElfExeOutput.AllocGOTSlot(objsym:TObjSymbol):boolean;
      var
        exesym: TExeSymbol;
      begin
        result:=false;
        exesym:=objsym.exesymbol;

        { Although local symbols should not be accessed through GOT,
          this isn't strictly forbidden. In this case we need to fake up
          the exesym to store the GOT offset in it.
          TODO: name collision; maybe use a different symbol list object? }
        if exesym=nil then
          begin
            exesym:=TExeSymbol.Create(ExeSymbolList,objsym.name+'*local*');
            exesym.objsymbol:=objsym;
            objsym.exesymbol:=exesym;
          end;
        if exesym.GotOffset>0 then
          exit;
        gotobjsec.alloc(sizeof(pint));
        exesym.GotOffset:=gotobjsec.size;
        make_dynamic_if_undefweak(exesym);
        { In shared library, every GOT entry needs a RELATIVE dynamic reloc,
          imported/exported symbols need GLOB_DAT instead. For executables,
          only the latter applies. }
        if IsSharedLibrary or (exesym.dynindex>0) then
          dynrelocsec.alloc(dynrelocsec.shentsize);
        result:=true;
      end;


    procedure TElfExeOutput.PrepareGOT;
      var
        i,j,k: longint;
        objsec: TElfObjSection;
        exesec: TExeSection;
      begin
        for i:=0 to ExeSectionList.Count-1 do
          begin
            exesec:=TExeSection(ExeSectionList[i]);
            for j:=0 to exesec.ObjSectionlist.count-1 do
              begin
                objsec:=TElfObjSection(exesec.ObjSectionlist[j]);
                { ignore linker-generated and debug sections }
                if (objsec.objdata=internalobjdata) or (oso_debug in objsec.SecOptions) then
                  continue;
                if not objsec.Used then
                  internalerror(2012060901);
                k:=0;
                while k<objsec.ObjRelocations.Count do
                  begin
                    GOTRelocPass1(objsec,k);
                    inc(k);
                  end;
              end;
          end;
        { remember sizes for sanity checking }
        gotsize:=gotobjsec.size;
        if assigned(dynrelocsec) then
          dynrelsize:=dynrelocsec.size
        else
          dynrelsize:=0;
      end;


    procedure TElfExeOutput.CreateGOTSection;
      begin
        gotpltobjsec:=TElfObjSection.create_ext(internalObjData,'.got.plt',
          SHT_PROGBITS,SHF_ALLOC or SHF_WRITE,sizeof(pint),sizeof(pint));

        gotobjsec:=TElfObjSection.create_ext(internalObjData,'.got',
            SHT_PROGBITS,SHF_ALLOC or SHF_WRITE,sizeof(pint),sizeof(pint));
        gotobjsec.SecOptions:=[oso_keep];

        { GOT symbol and reserved .got.plt entries }
        internalObjData.SetSection(gotpltobjsec);
        gotsymbol:=internalObjData.SymbolDefine('_GLOBAL_OFFSET_TABLE_',AB_GLOBAL,AT_DATA);
        gotpltobjsec.writeZeros(3*sizeof(pint));
      end;


    procedure TElfExeOutput.Load_Start;
      begin
        inherited Load_Start;
        dynsymlist:=TFPObjectList.Create(False);
        CreateGOTSection;
      end;


    procedure TElfExeOutput.Load_DynamicObject(objdata:TObjData;asneeded:boolean);
      var
        i: longint;
        exesym: TExeSymbol;
        objsym: TObjSymbol;
        needed: boolean;
      begin
        Comment(v_debug,'Dynamic object: '+objdata.name);
        needed:=false;
        for i:=0 to UnresolvedExeSymbols.Count-1 do
          begin
            exesym:=TExeSymbol(UnresolvedExeSymbols[i]);
            if not (exesym.State in [symstate_undefined,symstate_undefweak]) then
              continue;
            objsym:=TObjSymbol(objdata.ObjSymbolList.Find(exesym.name));
            if assigned(objsym) then
              begin
                exesym.State:=symstate_defined;
                exesym.dynindex:=dynsymlist.Add(exesym)+1;
                { The original binding, value and section of external symbol
                  must be preserved, therefore resolving directly to .so symbol
                  hurts more than it helps. Copy type and size, and store .so
                  symbol in objsym.indsymbol for later use. }
                exesym.ObjSymbol.typ:=objsym.typ;
                if objsym.typ<>AT_FUNCTION then
                  exesym.ObjSymbol.size:=objsym.size;
                exesym.ObjSymbol.indsymbol:=objsym;
                objsym.ExeSymbol:=exesym;
                needed:=true;
              end;
          end;
        if (needed or (not asneeded)) and
          (neededlist.Find(objdata.name)=nil) then
          neededlist.Add(objdata.name,objdata);
      end;


    procedure TElfExeOutput.Order_Start;
      begin
        inherited Order_Start;
        dynamiclink:=IsSharedLibrary or (dynsymlist.count>0) or
          (
            (UnresolvedExeSymbols.Count>0) and
            not (cs_link_staticflag in current_settings.globalswitches)
          );
        if dynamiclink then
          InitDynlink;
        if dynamiclink or (IndirectObjSymbols.Count>0) then
          CreatePLT;
      end;


    procedure TElfExeOutput.Order_end;

      procedure set_oso_keep(const s:string;out firstsec:TObjSection);
        var
          exesec:TExeSection;
          objsec:TObjSection;
          i:longint;
          sz: aword;
        begin
          firstsec:=nil;
          sz:=0;
          exesec:=TExeSection(ExeSectionList.Find(s));
          if assigned(exesec) then
            begin
              for i:=0 to exesec.ObjSectionList.Count-1 do
                begin
                  objsec:=TObjSection(exesec.ObjSectionList[i]);
                  { ignore sections used for symbol definition }
                  if oso_data in objsec.SecOptions then
                    begin
                      if firstsec=nil then
                        firstsec:=objsec;
                      objsec.SecOptions:=[oso_keep];
                      inc(sz,objsec.size);
                    end;
                end;
              exesec.size:=sz;
            end;
        end;

      var
        dummy: TObjSection;
      begin
        OrderOrphanSections;
        inherited Order_end;
        set_oso_keep('.init',dummy);
        set_oso_keep('.fini',dummy);
        set_oso_keep('.jcr',dummy);
        set_oso_keep('.ctors',dummy);
        set_oso_keep('.dtors',dummy);
        set_oso_keep('.preinit_array',preinitarraysec);
        if assigned(preinitarraysec) and IsSharedLibrary then
          Comment(v_error,'.preinit_array section is not allowed in shared libraries');
        set_oso_keep('.init_array',initarraysec);
        set_oso_keep('.fini_array',finiarraysec);
        set_oso_keep('.eh_frame',dummy);

        { let .dynamic reference other dynamic sections so they aren't marked
          for removal as unused }
        if dynamiclink then
          WriteDynamicTags;
      end;


    procedure TElfExeOutput.OrderOrphanSections;
      var
        i,j:longint;
        objdata:TObjData;
        objsec:TObjSection;
        exesec:TExeSection;
        opts:TObjSectionOptions;
        s:string;
        newsections:TFPHashObjectList;
        allsections:TFPList;
        inserts:array[0..6] of TExeSection;
        idx,inspos:longint;
      begin
        newsections:=TFPHashObjectList.Create(false);
        allsections:=TFPList.Create;
        { copy existing sections }
        for i:=0 to ExeSectionList.Count-1 do
          allsections.add(ExeSectionList[i]);
        inserts[0]:=FindExeSection('.comment');
        inserts[1]:=nil;
        inserts[2]:=FindExeSection('.interp');
        inserts[3]:=FindExeSection('.bss');
        inserts[4]:=FindExeSection('.data');
        inserts[5]:=FindExeSection('.rodata');
        inserts[6]:=FindExeSection('.text');

        for i:=0 to ObjDataList.Count-1 do
          begin
            ObjData:=TObjData(ObjDataList[i]);
            for j:=0 to ObjData.ObjSectionList.Count-1 do
              begin
                objsec:=TObjSection(ObjData.ObjSectionList[j]);
                if objsec.Used then
                  continue;
                s:=objsec.name;
                exesec:=TExeSection(newsections.Find(s));
                if assigned(exesec) then
                  begin
                    exesec.AddObjSection(objsec);
                    continue;
                  end;
                opts:=objsec.SecOptions*[oso_data,oso_load,oso_write,oso_executable];
                if (objsec.SecOptions*[oso_load,oso_debug]=[]) then
                  { non-alloc, after .comment
                    GNU ld places .comment between stabs and dwarf debug info }
                  inspos:=0
                else if not (oso_load in objsec.SecOptions) then
                  inspos:=1   { debugging, skip }
                else if (oso_load in objsec.SecOptions) and
                  (TElfObjSection(objsec).shtype=SHT_NOTE) then
                  inspos:=2   { after .interp }
                else if (opts=[oso_load,oso_write]) then
                  inspos:=3   { after .bss }
                else if (opts=[oso_data,oso_load,oso_write]) then
                  inspos:=4   { after .data }
                else if (opts=[oso_data,oso_load]) then
                  inspos:=5   { rodata, relocs=??? }
                else if (opts=[oso_data,oso_load,oso_executable]) then
                  inspos:=6   { text }
                else
                  begin
                    Comment(v_debug,'Orphan section '+objsec.fullname+' has attributes that are not handled!');
                    continue;
                  end;
                if (inserts[inspos]=nil) then
                  begin
                    Comment(v_debug,'Orphan section '+objsec.fullname+': nowhere to insert, ignored');
                    continue;
                  end;
                idx:=allsections.IndexOf(inserts[inspos]);
                exesec:=CExeSection.Create(newsections,s);
                allsections.Insert(idx+1,exesec);
                inserts[inspos]:=exesec;
                exesec.AddObjSection(objsec);
              end;
          end;
        { Now replace the ExeSectionList with content of allsections }
        if (newsections.count<>0) then
          ReplaceExeSectionList(allsections);
        newsections.Free;
        allsections.Free;
      end;


    procedure TElfExeOutput.AfterUnusedSectionRemoval;
      var
        i:longint;
        exesym:TExeSymbol;
        objsym:TObjSymbol;
        objsec: TObjSection;
      begin
        { Unused section removal sets Used property of referenced exesymbols.
          Remaining ones can be removed. }
        for i:=0 to dynsymlist.count-1 do
          begin
            exesym:=TExeSymbol(dynsymlist[i]);
            if assigned(exesym.ObjSymbol.ObjSection) then  // an exported symbol
              continue;
            if not exesym.used then
              begin
                dynsymlist[i]:=nil;
                exesym.dynindex:=0;
              end;
          end;
        dynsymlist.Pack;
        { reindex }
        for i:=0 to dynsymlist.count-1 do
          TExeSymbol(dynsymlist[i]).dynindex:=i+1;

        { Drop unresolved symbols that aren't referenced, assign dynamic
          indices to remaining ones, but not if linking with -Xt.
          TODO: behavior of .so with -Xt ? }
        if (cs_link_staticflag in current_settings.globalswitches) then
          UnresolvedExeSymbols.Clear
        else
        for i:=0 to UnresolvedExeSymbols.Count-1 do
          begin
            exesym:=TExeSymbol(UnresolvedExeSymbols[i]);
            if exesym.used then
              begin
                if exesym.dynindex<>0 then
                  InternalError(2012062301);
                { Weak-referenced symbols are changed into dynamic ones
                  only if referenced through GOT or PLT (this is BFD-compatible) }
                if exesym.state<>symstate_undefweak then
                  exesym.dynindex:=dynsymlist.add(exesym)+1;
              end
            else
              UnresolvedExeSymbols[i]:=nil;
          end;
        UnresolvedExeSymbols.Pack;

        { Scan relocations to determine size of GOT, dynamic reloc section, etc. }
        PrepareGOT;

        { Write required PLT entries }
        for i:=0 to dynsymlist.Count-1 do
          begin
            exesym:=TExeSymbol(dynsymlist[i]);
            if assigned(exesym.ObjSymbol.objsection) then  // an exported symbol
              continue;

            if ((exesym.ObjSymbol.refs and symref_plt)<>0) or
              ((exesym.ObjSymbol.typ in [AT_FUNCTION,AT_GNU_IFUNC]) and (not IsSharedLibrary)) then
              begin
                make_dynamic_if_undefweak(exesym);

                { This symbol has a valid address to which relocations are resolved,
                  but it remains (weak)external when written to dynamic symtable. }
                objsym:=internalobjdata.CreateSymbol(exesym.name);
                objsym.typ:=AT_FUNCTION;
                objsym.bind:=exesym.ObjSymbol.bind;  { AB_EXTERNAL or AB_WEAK_EXTERNAL }
                objsym.indsymbol:=exesym.ObjSymbol.indsymbol;
                objsym.offset:=pltobjsec.size;
                objsym.objsection:=pltobjsec;
                objsym.exesymbol:=exesym;
                exesym.ObjSymbol:=objsym;

                WritePLTEntry(exesym);
              end
            else if ((exesym.ObjSymbol.refs and symref_from_text)<>0) and
              (exesym.ObjSymbol.typ<>AT_FUNCTION) and (not IsSharedLibrary) and
              (exesym.state<>symstate_undefweak) then
              begin
                if exesym.ObjSymbol.size=0 then
                  Comment(v_error,'Dynamic variable '+exesym.name+' has zero size');
                internalobjdata.setSection(dynbssobjsec);
                internalobjdata.allocalign(size_2_align(exesym.ObjSymbol.size));
                objsym:=internalobjdata.SymbolDefine(exesym.name,AB_GLOBAL,AT_DATA);
                objsym.size:=exesym.ObjSymbol.size;
                objsym.indsymbol:=exesym.ObjSymbol.indsymbol;
                exesym.ObjSymbol:=objsym;
                objsym.exesymbol:=exesym;
                dynbssobjsec.alloc(objsym.size);
                { allocate space for R_xx_COPY relocation for this symbol;
                  we'll create it later, to be consistent with "-z combreloc" semantics }
                dyncopysyms.add(objsym);
                dynrelocsec.alloc(dynrelocsec.shentsize);
                inc(dynrelsize,dynrelocsec.shentsize);
              end;
          end;

        { Handle indirect symbols }
        for i:=0 to IndirectObjSymbols.Count-1 do
          begin
            objsym:=TObjSymbol(IndirectObjSymbols[i]);
            objsec:=objsym.ExeSymbol.ObjSymbol.objsection;
            objsym.bind:=AB_EXTERNAL;  { cheat FixupSymbols }
            if (oso_plt in objsec.SecOptions) then
              continue;
            WriteIndirectPLTEntry(objsym.ExeSymbol);
          end;

        FixupSymbols;

        if dynamiclink then
          begin
            WriteVersionSections;
            WriteDynamicSymbolsHash;
          end;

        { Create .shstrtab section, which is needed in both exe and .dbg files }
        shstrtabsect:=TElfObjSection.Create_ext(internalObjData,'.shstrtab',SHT_STRTAB,0,1,0);
        shstrtabsect.SecOptions:=[oso_debug_copy];
        AttachSection(shstrtabsect);

        { Create the static symtable (.symtab and .strtab) }
        if (cs_link_separate_dbg_file in current_settings.globalswitches) or
          not(cs_link_strip in current_settings.globalswitches) then
          begin
            symtab:=TElfSymtab.Create(internalObjData,esk_exe);
            symtab.SecOptions:=[oso_debug];
            symtab.fstrsec.SecOptions:=[oso_debug];
            AttachSection(symtab);
            AttachSection(symtab.fstrsec);
          end;

        { Re-enable sections which end up to contain some data
          (.got, .rel[a].dyn, .rel[a].plt (includes .rel[a].iplt) and .hash }
        if gotobjsec.size<>0 then
          gotobjsec.ExeSection.Disabled:=false;
        if assigned(dynrelocsec) and
          ((dynrelocsec.size<>0) or (dyncopysyms.count<>0)) then
          dynrelocsec.ExeSection.Disabled:=false;
        if assigned(pltrelocsec) and (pltrelocsec.size>0) then
          pltrelocsec.ExeSection.Disabled:=false;
        if assigned(ipltrelocsec) and (ipltrelocsec.size>0) then
          ipltrelocsec.ExeSection.Disabled:=false;
        if assigned(hashobjsec) then
          hashobjsec.ExeSection.Disabled:=false;
        if assigned(symversec) and (symversec.size<>0) then
          symversec.ExeSection.Disabled:=false;
        if assigned(verneedsec) and (verneedsec.size<>0) then
          verneedsec.ExeSection.Disabled:=false;
        if assigned(verdefsec) and (verdefsec.size<>0) then
          verdefsec.ExeSection.Disabled:=false;

        RemoveDisabledSections;
        MapSectionsToSegments;
        if dynamiclink then
          FinishDynamicTags;
      end;


    procedure TElfExeOutput.WriteShStrtab;
      var
        i: longint;
        exesec: TElfExeSection;
      begin
        { Remove any existing .shstrtab contents }
        if (shstrtabsect.size>0) then
          begin
            shstrtabsect.ReleaseData;
            shstrtabsect.Size:=0;
            shstrtabsect.SecOptions:=[oso_data];
          end;

        shstrtabsect.writezeros(1);
        for i:=0 to ExeSectionList.Count-1 do
          begin
            exesec:=TElfExeSection(ExeSectionList[i]);
            exesec.shstridx:=shstrtabsect.writestr(exesec.Name);
            exesec.secshidx:=i+1;
          end;
      end;


    procedure TElfExeOutput.FixupSectionLinks;
      var
        dynstrndx,dynsymndx: longword;
      begin
        if dynamiclink then
          begin
            dynstrndx:=TElfExeSection(dynsymtable.fstrsec.ExeSection).secshidx;
            dynsymndx:=TElfExeSection(dynsymtable.ExeSection).secshidx;
            TElfExeSection(hashobjsec.ExeSection).shlink:=dynsymndx;
            TElfExeSection(dynamicsec.ExeSection).shlink:=dynstrndx;
            TElfExeSection(dynsymtable.ExeSection).shlink:=dynstrndx;

            if assigned(pltrelocsec) then
              begin
                TElfExeSection(pltrelocsec.ExeSection).shlink:=dynsymndx;
                TElfExeSection(pltrelocsec.ExeSection).shinfo:=TElfExeSection(pltobjsec.ExeSection).secshidx;
              end;

            if assigned(dynrelocsec) and assigned(dynrelocsec.ExeSection) then
              TElfExeSection(dynrelocsec.ExeSection).shlink:=dynsymndx;

            if symversec.size>0 then
              TElfExeSection(symversec.ExeSection).shlink:=dynsymndx;
            if verdefsec.size>0 then
              TElfExeSection(verdefsec.ExeSection).shlink:=dynstrndx;
            if verneedsec.size>0 then
              TElfExeSection(verneedsec.ExeSection).shlink:=dynstrndx;
          end
        else if assigned(ipltrelocsec) then
          TElfExeSection(ipltrelocsec.ExeSection).shinfo:=TElfExeSection(pltobjsec.ExeSection).secshidx;
      end;


    procedure TElfExeOutput.Do_Mempos;
      var
        i,j: longint;
        seg: TElfSegment;
        exesec: TElfExeSection;
        objsec: TObjSection;
        tempmempos: qword;
      begin
        if IsSharedLibrary then
          CurrMemPos:=0
        else
          CurrMemPos:=ElfTarget.exe_image_base;
        textseg.MemPos:=CurrMemPos;
        if assigned(phdrseg) then
          begin
            phdrseg.Mempos:=CurrMemPos+sizeof(TElfHeader);
            phdrseg.Memsize:=sizeof(TElfproghdr)*segmentlist.count;
          end;
        CurrMemPos:=CurrMemPos+sizeof(TElfHeader)+segmentlist.count*sizeof(TElfproghdr);
        MemPos_Segment(textseg);
        CurrMemPos:=Align(CurrMemPos,SectionDataAlign); {! Data,not MemAlign}
        CurrMemPos:=CurrMemPos+ElfTarget.max_page_size;
        dataseg.MemPos:=CurrMemPos;
        MemPos_Segment(dataseg);
        { Mempos of unmapped sections is forced to zero, but we have to set positions
          of its objsections and update sizes }
        for i:=0 to ExeSectionList.Count-1 do
          begin
            exesec:=TElfExeSection(ExeSectionList[i]);
            if not (oso_load in exesec.SecOptions) then
              begin
                tempmempos:=0;
                exesec.MemPos:=tempmempos;
                for j:=0 to exesec.ObjSectionList.Count-1 do
                  begin
                    objsec:=TObjSection(exesec.ObjSectionList[j]);
                    tempmempos:=objsec.setmempos(tempmempos);
                  end;
                exesec.Size:=tempmempos;
              end;
          end;

        { Update MemPos and MemSize of non-load segments,
          in particular, TLS sizes are needed to resolve relocations }
        for i:=0 to segmentlist.count-1 do
          begin
            seg:=TElfSegment(segmentlist[i]);
            if (seg.ptype=PT_LOAD) or (seg.FSectionList.Count=0) then
              continue;
            seg.MemPos:=TExeSection(seg.FSectionList.First).MemPos;
            for j:=0 to seg.FSectionList.Count-1 do
              begin
                exesec:=TElfExeSection(seg.FSectionList[j]);
                seg.MemSize:=exesec.MemPos+exesec.Size-seg.MemPos;
              end;
          end;
      end;


    procedure TElfExeOutput.MemPos_Start;
      var
        i: longint;
      begin
        { Assign section indices and fill .shstrtab
          List of sections cannot be modified after this point. }
        WriteShStrtab;

        { fixup sh_link/sh_info members of various dynamic sections }
        FixupSectionLinks;

        { The actual layout }
        Do_Mempos;

        if (not gotwritten) then
          begin
            { Reset size of .got and .rel[a].dyn, they will be refilled while fixing up relocations.
              For .got, consider already written reserved entries. }
            if assigned(gotobjsec) then
              gotobjsec.size:=gotobjsec.data.size;
            if assigned(dynrelocsec) then
              begin
                dynrelocsec.size:=0;
                { write actual .dynsym content (needs valid symbol addresses) }
                if assigned(tlsseg) then
                  dynsymtable.tlsbase:=tlsseg.MemPos;
                dynsymtable.size:=sizeof(TElfsymbol);
                for i:=0 to dynsymlist.count-1 do
                  dynsymtable.writeSymbol(TExeSymbol(dynsymlist[i]).objsymbol,dynsymnames[i]);
              end;
          end;
      end;


    procedure TElfExeOutput.MemPos_Segment(seg:TElfSegment);
      var
        i: longint;
        exesec: TElfExeSection;
      begin
        for i:=0 to seg.FSectionList.Count-1 do
          begin
            exesec:=TElfExeSection(seg.FSectionList[i]);
            inherited MemPos_ExeSection(exesec);
            { .tbss should not contribute to address space }
            if (exesec.shtype=SHT_NOBITS) and ((exesec.shflags and SHF_TLS)<>0) then
              CurrMemPos:=exesec.MemPos;
          end;
        { calculate size of the segment }
        seg.MemSize:=CurrMemPos-seg.MemPos;
      end;


    procedure TElfExeOutput.MemPos_ExeSection(const aname:string);
      begin
        // Ignore. All layout is done in mempos_start
      end;


    procedure TElfExeOutput.DataPos_Start;
      var
        i,j: longint;
        exesec: TExeSection;
        seg: TElfSegment;
        objreloc: TObjRelocation;
        objsym: TObjSymbol;
      begin
        gotwritten:=true;
        { If target does not support sorted relocations, it is expected to write the
          entire .rel[a].dyn section during FixupRelocations, and leave dynreloclist empty.
          Otherwise, only RELATIVE ones should be written, space for non-relative relocations
          should remain. }
        if assigned(dynrelocsec) then
          begin
            { Append R_xx_COPY relocations }
            for i:=0 to dyncopysyms.count-1 do
              begin
                objsym:=TObjSymbol(dyncopysyms[i]);
                dynreloclist.Add(TObjRelocation.CreateRaw(objsym.address,objsym,ElfTarget.dyn_reloc_codes[dr_copy]));
              end;
            dyncopysyms.Clear;

            if (dynrelocsec.size+(dynreloclist.count*dynrelocsec.shentsize)<>dynrelsize) then
              InternalError(2012110601);
            { Write out non-RELATIVE dynamic relocations
              TODO: additional sorting? }
            for i:=0 to dynreloclist.count-1 do
              begin
                objreloc:=TObjRelocation(dynreloclist[i]);
                WriteDynRelocEntry(objreloc.dataoffset,objreloc.ftype,objreloc.symbol.exesymbol.dynindex,0);
              end;
          end;

        { sanity checks }
        if assigned(gotobjsec) and (gotsize<>gotobjsec.size) then
          InternalError(2012092501);
        if assigned(dynrelocsec) and (dynrelsize<>dynrelocsec.size) then
          InternalError(2012092502);

        if (ExeWriteMode=ewm_dbgonly) or
          (
            (ExeWriteMode=ewm_exefull) and
             not(cs_link_strip in current_settings.globalswitches)
          ) then
          WriteStaticSymtable;

        { first handle primary segments }
        textseg.DataPos:=0;
        CurrDataPos:=sizeof(TElfHeader)+sizeof(TElfproghdr)*segmentlist.count;
        if assigned(phdrseg) then
          begin
            phdrseg.DataPos:=sizeof(TElfHeader);
            phdrseg.DataSize:=sizeof(TElfproghdr)*segmentlist.count;
          end;
        DataPos_Segment(textseg);
        CurrDataPos:=align(CurrDataPos,SectionDataAlign);
        dataseg.DataPos:=CurrDataPos;
        DataPos_Segment(dataseg);
        { then unmapped sections }
        for i:=0 to ExeSectionList.Count-1 do
          begin
            exesec:=TExeSection(ExeSectionList[i]);
            if not (oso_load in exesec.SecOptions) then
              inherited DataPos_ExeSection(exesec);
          end;
        { finally, update size/position of non-load segments }
        for i:=0 to segmentlist.count-1 do
          begin
            seg:=TElfSegment(segmentlist[i]);
            if (seg.ptype=PT_LOAD) or (seg.FSectionList.Count=0) then
              continue;
            seg.DataPos:=TExeSection(seg.FSectionList.First).DataPos;
            for j:=0 to seg.FSectionList.Count-1 do
              begin
                exesec:=TExeSection(seg.FSectionList[j]);
                if oso_data in exesec.SecOptions then
                  seg.DataSize:=exesec.DataPos+exesec.Size-seg.DataPos;
              end;
          end;
        { place section headers after the data }
        shoffset:=CurrDataPos;
        CurrDataPos:=CurrDataPos+ExeSectionList.Count*sizeof(TElfsechdr);
      end;


    procedure TElfExeOutput.DataPos_Segment(seg:TElfSegment);
      var
        i: longint;
        exesec: TElfExeSection;
      begin
        for i:=0 to seg.FSectionList.Count-1 do
          begin
            exesec:=TElfExeSection(seg.FSectionList[i]);
            { ELF needs DataPos set to 'would-be' value for sections that
              don't have data, and for non-debug sections in .dbg file, too.
              This slightly differs from generic approach. }
            if not (oso_data in exesec.SecOptions) or
              (
                (ExeWriteMode=ewm_dbgonly) and
                (exesec.SecOptions*[oso_debug,oso_debug_copy]=[])
              ) then
              begin
                CurrDataPos:=align(CurrDataPos,SectionDataAlign);
                exesec.DataPos:=CurrDataPos;
              end
            else
              inherited DataPos_ExeSection(exesec);

          end;
        { calculate size of the segment }
        seg.DataSize:=CurrDataPos-seg.DataPos;
      end;


    procedure TElfExeOutput.DataPos_ExeSection(const aname:string);
      begin
        // Ignore. Work is done entirely in datapos_start.
      end;


    procedure TElfExeOutput.InitDynlink;
      begin
        if not IsSharedLibrary then
          begin
            interpobjsec:=internalObjData.createsection('.interp',1,[oso_data,oso_load,oso_keep]);
            interpobjsec.writestr(interpreter^);
          end;

        hashobjsec:=TElfObjSection.create_ext(internalObjData,'.hash',
          SHT_HASH,SHF_ALLOC,sizeof(pint),4);
        hashobjsec.secoptions:=[oso_keep];

        dynsymtable:=TElfSymtab.create(internalObjData,esk_dyn);

        dynamicsec:=TElfObjSection.create_ext(internalObjData,'.dynamic',
          SHT_DYNAMIC,SHF_ALLOC or SHF_WRITE,sizeof(pint),sizeof(TElfDyn));
        dynamicsec.SecOptions:=[oso_keep];

        dynrelocsec:=TElfObjSection.create_reloc(internalObjData,'.dyn',true);
        dynrelocsec.SecOptions:=[oso_keep];

        dynbssobjsec:=TElfObjSection.create_ext(internalObjData,'.dynbss',
          SHT_NOBITS,SHF_ALLOC or SHF_WRITE,sizeof(pint){16??},0);
        dynbssobjsec.SecOptions:=[oso_keep];

        dynreloclist:=TFPObjectList.Create(true);

        symversec:=TElfObjSection.create_ext(internalObjData,'.gnu.version',
          SHT_GNU_VERSYM,SHF_ALLOC,sizeof(word),sizeof(word));
        symversec.SecOptions:=[oso_keep];
        verdefsec:=TElfObjSection.create_ext(internalObjData,'.gnu.version_d',
          SHT_GNU_VERDEF,SHF_ALLOC,sizeof(pint),0);
        verdefsec.SecOptions:=[oso_keep];
        verneedsec:=TElfObjSection.create_ext(internalObjData,'.gnu.version_r',
          SHT_GNU_VERNEED,SHF_ALLOC,sizeof(pint),0);
        verneedsec.SecOptions:=[oso_keep];
        dyncopysyms:=TFPObjectList.Create(False);
      end;


    const
      hashbuckets: array[0..15] of longint=(
        1, 3, 17, 37, 67, 97, 131, 197, 263, 521, 1031, 2053, 4099, 8209,
        16411, 32771);

{$push}{$r-,q-}
    function elfhash(const name:string):longword;
      var
        g: longword;
        i: longint;
      begin
        result:=0;
        for i:=1 to length(name) do
        begin
          result:=(result shl 4)+ord(name[i]);
          g:=result and $F0000000;
          if g>0 then
            result:=result xor (g shr 24);
          result:=result and (not g);
        end;
      end;
{$pop}

    procedure TElfExeOutput.WriteDynamicSymbolsHash;
      var
        nchains,nbuckets: longint;
        i,j: longint;
        hashdata: plongint;
        sym: TExeSymbol;
      begin
        dynsymnames:=AllocMem(dynsymlist.count*sizeof(longword));
        nchains:=dynsymlist.Count+1;
        { determine suitable bucket count }
        i:=high(hashbuckets);
        while (i>=0) and (nchains<hashbuckets[i]) do
          dec(i);
        nbuckets:=hashbuckets[i];

        hashdata:=AllocMem((2+nchains+nbuckets)*sizeof(longint));
        hashdata[0]:=nbuckets;
        hashdata[1]:=nchains;
        { The contents of .dynsym can be written only after mempos pass
          because it needs valid symbol virtual addresses and section indices.
          Here we preset .dynsym size and write names, in order to get
          correct size of .dynstr section. }
        dynsymtable.size:=(dynsymlist.count+1)*sizeof(TElfsymbol);
        for i:=0 to dynsymlist.Count-1 do
          begin
            sym:=TExeSymbol(dynsymlist[i]);
            dynsymnames[i]:=dynsymtable.fstrsec.writestr(sym.objsymbol.name);
            j:=(elfhash(sym.objsymbol.name) mod nbuckets)+2;

            while hashdata[j]<>0 do
              j:=2+nbuckets+hashdata[j];
            hashdata[j]:=i+1;
          end;
        if source_info.endian<>target_info.endian then
          for i:=0 to nchains+nbuckets+1 do
            hashdata[i]:=swapendian(hashdata[i]);
        hashobjsec.write(hashdata^,(2+nchains+nbuckets)*sizeof(longint));
        freemem(hashdata);
      end;


    procedure TElfExeOutput.WriteVersionSections;
      var
        i,j: longint;
        idx,auxidx: longword;
        exesym: TExeSymbol;
        dynobj: TElfDynamicObjData;
        ver: TElfVersionDef;
        vn: TElfverneed;
        vna: TElfvernaux;
        symversions: pword;
      begin
        symversions:=AllocMem((dynsymlist.count+1)*sizeof(word));
        { Assign version indices }
        idx:=VER_NDX_GLOBAL+1;
        for i:=0 to dynsymlist.count-1 do
          begin
            exesym:=TExeSymbol(dynsymlist[i]);
            if (exesym.objsymbol.indsymbol is TVersionedObjSymbol) then
              ver:=TVersionedObjSymbol(exesym.objsymbol.indsymbol).version
            else
              ver:=nil;
            if assigned(ver) then
              begin
                if ver.index=0 then
                  begin
                    ver.index:=idx;
                    inc(idx);
                  end;
                symversions[i+1]:=ver.index;
              end
            else if exesym.state in [symstate_undefined,symstate_undefweak] then
              symversions[i+1]:=VER_NDX_LOCAL
            else
              symversions[i+1]:=VER_NDX_GLOBAL;
          end;

        { Count entries to be written }
        verneedcount:=0;
        for i:=0 to neededlist.count-1 do
          begin
            dynobj:=TElfDynamicObjData(neededlist[i]);
            dynobj.vernaux_count:=0;
            for j:=2 to dynobj.versiondefs.count-1 do
              begin
                ver:=TElfVersionDef(dynobj.versiondefs[j]);
                if ver.index>VER_NDX_GLOBAL then
                  inc(dynobj.vernaux_count);
              end;
            if (dynobj.vernaux_count>0) then
              inc(verneedcount);
          end;

        { Now write }
        idx:=0;
        for i:=0 to neededlist.count-1 do
          begin
            dynobj:=TElfDynamicObjData(neededlist[i]);
            if dynobj.vernaux_count=0 then
              continue;
            inc(idx);
            vn.vn_version:=VER_NEED_CURRENT;
            vn.vn_cnt:=dynobj.vernaux_count;
            vn.vn_file:=dynobj.soname_strofs;
            vn.vn_aux:=sizeof(TElfverneed);
            vn.vn_next:=ord(idx<verneedcount)*(sizeof(TElfverneed)+vn.vn_cnt*sizeof(TElfvernaux));
            MaybeSwapElfverneed(vn);
            verneedsec.write(vn,sizeof(TElfverneed));

            auxidx:=0;
            for j:=2 to dynobj.versiondefs.count-1 do
              begin
                ver:=TElfVersionDef(dynobj.versiondefs[j]);
                if ver.index<=VER_NDX_GLOBAL then
                  continue;
                inc(auxidx);
                vna.vna_hash:=elfhash(ver.name);
                vna.vna_flags:=0;   { BFD copies this from verdef.vd_flags?? }
                vna.vna_other:=ver.index;
                vna.vna_name:=dynsymtable.fstrsec.writestr(ver.name);
                vna.vna_next:=ord(auxidx<dynobj.vernaux_count)*sizeof(TElfvernaux);
                MaybeSwapElfvernaux(vna);
                verneedsec.write(vna,sizeof(TElfvernaux));
              end;
          end;
        TElfExeSection(verneedsec.ExeSection).shinfo:=verneedcount;

        { If there are no needed versions, .gnu.version section is not needed }
        if verneedcount>0 then
          begin
            if source_info.endian<>target_info.endian then
              for i:=0 to dynsymlist.count+1 do
                symversions[i]:=swapendian(symversions[i]);
            symversec.write(symversions^,(dynsymlist.count+1)*sizeof(word));
          end;
        FreeMem(symversions);
      end;


    procedure TElfExeOutput.WriteDynRelocEntry(dataofs:aword;typ:byte;symidx:aword;addend:aword);
      var
        rel:telfreloc;
      begin
        rel.address:=dataofs;
        rel.info:=ELF_R_INFO(symidx,typ);
{$push}{$r-}
        rel.addend:=addend;
{$pop}
        MaybeSwapElfReloc(rel);
        dynrelocsec.write(rel,dynrelocsec.shentsize);
      end;


    procedure TElfExeOutput.WriteDynTag(aTag:longword;aValue:longword);
      var
        d: TElfDyn;
      begin
        d.d_tag:=aTag;
        d.d_val:=aValue;
        MaybeSwapElfDyn(d);
        dynamicsec.write(d,sizeof(TElfDyn));
      end;


    procedure TElfExeOutput.WriteDynTag(aTag:longword;aSection:TObjSection;aOffs:aword);
      var
        d: TElfDyn;
      begin
        d.d_tag:=aTag;
        if source_info.endian<>target_info.endian then
          d.d_tag:=swapendian(d.d_tag);
        dynamicsec.write(d.d_tag,sizeof(d.d_tag));
        { TODO: ignores endianness! }
        dynamicsec.writeReloc_internal(aSection,aOffs,sizeof(d.d_ptr),RELOC_ABSOLUTE);
      end;


    procedure TElfExeOutput.WriteTargetDynamicTags;
      begin
        { to be overridden by CPU-specific descendants }
      end;


    procedure TElfExeOutput.WriteDynamicTags;
      var
        s: aword;
        i: longint;
        sym: TExeSymbol;
        hs:string;
        dynobj: TElfDynamicObjData;
      begin
        for i:=0 to neededlist.Count-1 do
          begin
            dynobj:=TElfDynamicObjData(neededlist[i]);
            s:=dynsymtable.fstrsec.writestr(dynobj.name);
            dynobj.soname_strofs:=s;
            WriteDynTag(DT_NEEDED,s);
          end;

        if IsSharedLibrary then
          begin
            s:=dynsymtable.fstrsec.writestr(ExtractFileName(current_module.sharedlibfilename));
            WriteDynTag(DT_SONAME,s);
            { TODO: names hardcoded here }
            sym:=TExeSymbol(ExeSymbolList.Find('FPC_SHARED_LIB_START'));
            if assigned(sym) then
              WriteDynTag(DT_INIT,sym.objsymbol.objsection,sym.objsymbol.offset);
            sym:=TExeSymbol(ExeSymbolList.Find('FPC_LIB_EXIT'));
            if assigned(sym) then
              WriteDynTag(DT_FINI,sym.objsymbol.objsection,sym.objsymbol.offset);
          end;

        { TODO: we need a dedicated parameter to pass runpath, instead of this hack
          (-Xr is a different thing, it passes "-rpath-link"). }
        if (ParaLinkOptions<>'') then
          begin
            hs:=ParaLinkOptions;
            while (hs<>'') do
              begin
                if (GetToken(hs,' ')='-rpath') then
                  begin
                    s:=dynsymtable.fstrsec.writestr(GetToken(hs,' '));
                    WriteDynTag(DT_RPATH,s);
                  end;
              end;
          end;

        if assigned(preinitarraysec) then
          begin
            WriteDynTag(DT_PREINIT_ARRAY,preinitarraysec,0);
            WriteDynTag(DT_PREINIT_ARRAYSZ,preinitarraysec.exesection.size);
          end;

        if assigned(initarraysec) then
          begin
            WriteDynTag(DT_INIT_ARRAY,initarraysec,0);
            WriteDynTag(DT_INIT_ARRAYSZ,initarraysec.exesection.size);
          end;

        if assigned(finiarraysec) then
          begin
            WriteDynTag(DT_FINI_ARRAY,finiarraysec,0);
            WriteDynTag(DT_FINI_ARRAYSZ,finiarraysec.exesection.size);
          end;

        writeDynTag(DT_HASH,hashobjsec);
        writeDynTag(DT_STRTAB,dynsymtable.fstrsec);
        writeDynTag(DT_SYMTAB,dynsymtable);

        writeDynTag(DT_SYMENT,sizeof(TElfSymbol));

        if Assigned(gotpltobjsec) then
          writeDynTag(DT_PLTGOT,gotpltobjsec);
      end;


    const
      pltreltags: array[boolean] of longword=(DT_REL,DT_RELA);
      relsztags:  array[boolean] of longword=(DT_RELSZ,DT_RELASZ);
      relenttags: array[boolean] of longword=(DT_RELENT,DT_RELAENT);
      {$ifndef MIPS}
      relcnttags: array[boolean] of longword=(DT_RELCOUNT,DT_RELACOUNT);
      {$endif MIPS}

    procedure TElfExeOutput.FinishDynamicTags;
      var
        rela: boolean;
      begin
        if assigned(dynsymtable) then
          writeDynTag(DT_STRSZ,dynsymtable.fstrsec.size);

        if hastextrelocs then
          writeDynTag(DT_TEXTREL,0);

        if Assigned(pltrelocsec) and (pltrelocsec.size>0) then
          begin
            writeDynTag(DT_PLTRELSZ,pltrelocsec.Size);
            writeDynTag(DT_PLTREL,pltreltags[pltrelocsec.shtype=SHT_RELA]);
            writeDynTag(DT_JMPREL,pltrelocsec);
          end;

        if Assigned(dynrelocsec) and (dynrelocsec.size>0) then
          begin
            rela:=(dynrelocsec.shtype=SHT_RELA);
            writeDynTag(pltreltags[rela],dynrelocsec);
            writeDynTag(relsztags[rela],dynrelocsec.Size);
            writeDynTag(relenttags[rela],dynrelocsec.shentsize);
{$ifndef MIPS}
            if (relative_reloc_count>0) then
              writeDynTag(relcnttags[rela],relative_reloc_count);
{$endif MIPS}
          end;

        WriteTargetDynamicTags;

        if (verdefcount>0) or (verneedcount>0) then
          begin
            if (verdefcount>0) then
              begin
                writeDynTag(DT_VERDEF,verdefsec);
                writeDynTag(DT_VERDEFNUM,verdefcount);
              end;
            if (verneedcount>0) then
              begin
                writeDynTag(DT_VERNEED,verneedsec);
                writeDynTag(DT_VERNEEDNUM,verneedcount);
              end;
            writeDynTag(DT_VERSYM,symversec);
          end;
        writeDynTag(DT_NULL,0);
      end;


    procedure TElfExeOutput.CreatePLT;
      var
        reloc: TObjRelocation;
      begin
        pltobjsec:=TElfObjSection.create_ext(internalObjData,'.plt',
          SHT_PROGBITS,SHF_ALLOC or SHF_EXECINSTR,4,16);
        pltobjsec.SecOptions:=[oso_keep,oso_plt];

        pltrelocsec:=TElfObjSection.create_reloc(internalObjData,'.plt',true);
        pltrelocsec.SecOptions:=[oso_keep];

        ipltrelocsec:=TElfObjSection.create_reloc(internalObjData,'.iplt',true);
        ipltrelocsec.SecOptions:=[oso_keep];

        { reference .dynamic from .got.plt, this isn't necessary if linking statically }
        { TODO: maybe move writing initial .got.plt entries here completely
          (needs testing --- GOT symbol may get lost if .got.plt is empty)}
        if dynamiclink then
          begin
            reloc:=TObjRelocation.CreateSection(0,dynamicsec,RELOC_ABSOLUTE);
            reloc.size:=sizeof(pint);
            gotpltobjsec.ObjRelocations.Add(reloc);
          end;

        { Initial PLT entry, CPU-specific }
        WriteFirstPLTEntry;
      end;


    procedure TElfExeOutput.WritePLTEntry(exesym:TExeSymbol);
      begin
        // must be implemented by CPU-specific descendant
        InternalError(2012092102);
      end;


    procedure TElfExeOutput.WriteIndirectPLTEntry(exesym:TExeSymbol);
      begin
        // must be implemented by CPU-specific descendant
        InternalError(2012092101);
      end;


    function TElfExeOutput.WriteData:boolean;
      begin
        WriteHeader;
        segmentlist.ForEachCall(@segment_write_header,nil);
        WriteExeSectionContent;
        FWriter.WriteZeros(sizeof(TElfsechdr));
        ExeSectionList.ForEachCall(@exesection_write_header,nil);
        result:=true;
      end;


    procedure TElfExeOutput.GenerateLibraryImports(ImportLibraryList:TFPHashObjectList);
      var
        exportlist: TCmdStrList;
        sym: TExeSymbol;
      begin
        AllowUndefinedSymbols:=IsSharedLibrary;
        { add exported symbols to dynamic list }
        exportlist:=texportlibunix(exportlib).exportedsymnames;
        if not exportlist.empty then
          repeat
            sym:=TExeSymbol(ExeSymbolList.Find(exportlist.getfirst));
            if assigned(sym) then
              begin
                if assigned(sym.objsymbol.objsection) then
                  sym.objsymbol.objsection.SecOptions:=[oso_keep];
                sym.dynindex:=dynsymlist.add(sym)+1
              end
            else
              InternalError(2012071801);
          until exportlist.empty;
      end;


    procedure TElfExeOutput.ReportNonDSOReloc(reltyp:byte;objsec:TObjSection;ObjReloc:TObjRelocation);
      begin
        { TODO: include objsec properties into message }
        Comment(v_error,'Relocation '+ElfTarget.RelocName(reltyp)+' against '''+objreloc.TargetName+''' cannot be used when linking a shared object; recompile with -Cg');
      end;


    procedure TElfExeOutput.ReportRelocOverflow(reltyp:byte;objsec:TObjSection;ObjReloc:TObjRelocation);
      begin
        { TODO: include objsec properties into message }
        Comment(v_error,'Relocation truncated to fit: '+ElfTarget.RelocName(reltyp)+' against '''+objreloc.TargetName+'''');
      end;


{****************************************************************************
                               TElfExeSection
****************************************************************************}

    procedure TElfExeSection.AddObjSection(objsec:TObjSection;ignoreprops:boolean);
      begin
        inherited AddObjSection(objsec,ignoreprops);
        if ignoreprops then
          exit;
        if (shtype=SHT_NULL) then
        begin
          shtype:=TElfObjSection(objsec).shtype;
          shflags:=TElfObjSection(objsec).shflags;
          shentsize:=TElfObjSection(objsec).shentsize;
        end;
      end;

{****************************************************************************
                                TElfSegment
****************************************************************************}

    constructor TElfSegment.Create(atype,aflags,aalign:longword);
      begin
        ptype:=atype;
        pflags:=aflags;
        align:=aalign;
        FSectionList:=TFPObjectList.Create(false);
      end;

    destructor TElfSegment.Destroy;
      begin
        FSectionList.Free;
        inherited Destroy;
      end;

    procedure TElfSegment.Add(exesec:TExeSection);
      begin
        FSectionList.Add(exesec);
      end;


end.