freepascal.compiler/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 }
       cpuinfo,cpubase,aasmbase,aasmtai,aasmdata,assemble,
       { output }
       ogbase,
       owbase;

    type
       TElfObjSection = class(TObjSection)
       public
          secshidx  : longint; { index for the section in symtab }
          shstridx,
          shtype,
          shflags,
          shlink,
          shinfo,
          shentsize : longint;
          constructor create(AList:TFPHashObjectList;const Aname:string;Aalign:shortint;Aoptions:TObjSectionOptions);override;
          constructor create_ext(AList:TFPHashObjectList;const Aname:string;Ashtype,Ashflags,Ashlink,Ashinfo:longint;Aalign:shortint;Aentsize:longint);
          destructor  destroy;override;
       end;

       TElfObjData = class(TObjData)
       public
         constructor create(const n:string);override;
         destructor  destroy;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,
         strtabsect,
         shstrtabsect: TElfObjSection;
         {gotpcsect,
         gotoffsect,
         goTSect,
         plTSect,
         symsect   : TElfObjSection;}
         elf32data : TElfObjData;
         symidx,
         localsyms : longint;
         procedure createrelocsection(s:TElfObjSection);
         procedure createshstrtab;
         procedure createsymtab;
         procedure writesectionheader(s:TElfObjSection);
         procedure writesectiondata(s:TElfObjSection);
         procedure write_internal_symbol(astridx:longint;ainfo:byte;ashndx:word);
         procedure section_write_symbol(p:TObject;arg:pointer);
         procedure section_write_sh_string(p:TObject;arg:pointer);
         procedure section_count_sections(p:TObject;arg:pointer);
         procedure section_create_relocsec(p:TObject;arg:pointer);
         procedure section_set_datapos(p:TObject;arg:pointer);
         procedure section_write_data(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;
         destructor Destroy;override;
       end;

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


implementation

      uses
        SysUtils,
        verbose,
        cutils,globals,fmodule;

    const
      symbolresize = 200*18;

    const
      { Relocation types }
{$ifdef i386}
      R_386_32 = 1;                    { ordinary absolute relocation }
      R_386_PC32 = 2;                  { PC-relative relocation }
      R_386_GOT32 = 3;                 { an offset into GOT }
      R_386_PLT32 = 4;                 { a PC-relative offset into PLT }
      R_386_GOTOFF = 9;                { an offset from GOT base }
      R_386_GOTPC = 10;                { a PC-relative offset _to_ GOT }
      R_386_GNU_VTINHERIT = 250;
      R_386_GNU_VTENTRY = 251;
{$endif i386}
{$ifdef sparc}
      R_SPARC_32 = 3;
      R_SPARC_WDISP30 = 7;
      R_SPARC_HI22 = 9;
      R_SPARC_LO10 = 12;
      R_SPARC_GNU_VTINHERIT = 250;
      R_SPARC_GNU_VTENTRY = 251;
{$endif sparc}
{$ifdef x86_64}
      R_X86_64_NONE = 0;
      { Direct 64 bit   }
      R_X86_64_64 = 1;
      { PC relative 32 bit signed  }
      R_X86_64_PC32 = 2;
      { 32 bit GOT entry  }
      R_X86_64_GOT32 = 3;
      { 32 bit PLT address  }
      R_X86_64_PLT32 = 4;
      { Copy symbol at runtime  }
      R_X86_64_COPY = 5;
      { Create GOT entry  }
      R_X86_64_GLOB_DAT = 6;
      { Create PLT entry  }
      R_X86_64_JUMP_SLOT = 7;
      { Adjust by program base  }
      R_X86_64_RELATIVE = 8;
      { 32 bit signed PC relative offset to GOT  }
      R_X86_64_GOTPCREL = 9;
      { Direct 32 bit zero extended  }
      R_X86_64_32 = 10;
      { Direct 32 bit sign extended  }
      R_X86_64_32S = 11;
      { Direct 16 bit zero extended  }
      R_X86_64_16 = 12;
      { 16 bit sign extended PC relative  }
      R_X86_64_PC16 = 13;
      { Direct 8 bit sign extended   }
      R_X86_64_8 = 14;
      { 8 bit sign extended PC relative  }
      R_X86_64_PC8 = 15;
      { ID of module containing symbol  }
      R_X86_64_DTPMOD64 = 16;
      { Offset in module's TLS block  }
      R_X86_64_DTPOFF64 = 17;
      { Offset in initial TLS block  }
      R_X86_64_TPOFF64 = 18;
      { 32 bit signed PC relative offset to two GOT entries for GD symbol  }
      R_X86_64_TLSGD = 19;
      { 32 bit signed PC relative offset to two GOT entries for LD symbol  }
      R_X86_64_TLSLD = 20;
      { Offset in TLS block  }
      R_X86_64_DTPOFF32 = 21;
      { 32 bit signed PC relative offset to GOT entry for IE symbol  }
      R_X86_64_GOTTPOFF = 22;
      { Offset in initial TLS block  }
      R_X86_64_TPOFF32 = 23;
      { GNU extension to record C++ vtable hierarchy }
      R_X86_64_GNU_VTINHERIT = 24;
      { GNU extension to record C++ vtable member usage }
      R_X86_64_GNU_VTENTRY = 25;
{$endif x86_64}

      SHN_UNDEF     = 0;
      SHN_ABS       = $fff1;
      SHN_COMMON    = $fff2;

      SHT_NULL     = 0;
      SHT_PROGBITS = 1;
      SHT_SYMTAB   = 2;
      SHT_STRTAB   = 3;
      SHT_RELA     = 4;
      SHT_HASH     = 5;
      SHT_DYNAMIC  = 6;
      SHT_NOTE     = 7;
      SHT_NOBITS   = 8;
      SHT_REL      = 9;
      SHT_SHLIB    = 10;
      SHT_DYNSYM   = 11;

      SHF_WRITE     = 1;
      SHF_ALLOC     = 2;
      SHF_EXECINSTR = 4;

      STB_LOCAL   = 0;
      STB_GLOBAL  = 1;
      STB_WEAK    = 2;

      STT_NOTYPE  = 0;
      STT_OBJECT  = 1;
      STT_FUNC    = 2;
      STT_SECTION = 3;
      STT_FILE    = 4;

      type
      { Structures which are written directly to the output file }
        TElf32header=packed record
          magic0123         : longint;
          file_class        : byte;
          data_encoding     : byte;
          file_version      : byte;
          padding           : array[$07..$0f] of byte;
          e_type            : word;
          e_machine         : word;
          e_version         : longint;
          e_entry           : longint;          { entrypoint }
          e_phoff           : longint;          { program header offset }
          e_shoff           : longint;          { sections header offset }
          e_flags           : longint;
          e_ehsize          : word;             { elf header size in bytes }
          e_phentsize       : word;             { size of an entry in the program header array }
          e_phnum           : word;             { 0..e_phnum-1 of entrys }
          e_shentsize       : word;             { size of an entry in sections header array }
          e_shnum           : word;             { 0..e_shnum-1 of entrys }
          e_shstrndx        : word;             { index of string section header }
        end;
        TElf32sechdr=packed record
          sh_name           : longint;
          sh_type           : longint;
          sh_flags          : longint;
          sh_addr           : longint;
          sh_offset         : longint;
          sh_size           : longint;
          sh_link           : longint;
          sh_info           : longint;
          sh_addralign      : longint;
          sh_entsize        : longint;
        end;
        TElf32reloc=packed record
          address : longint;
          info    : longint; { bit 0-7: type, 8-31: symbol }
        end;
        TElf32symbol=packed record
          st_name  : longint;
          st_value : longint;
          st_size  : longint;
          st_info  : byte; { bit 0-3: type, 4-7: bind }
          st_other : byte;
          st_shndx : word;
        end;


        telf64header=packed record
          magic0123         : longint;
          file_class        : byte;
          data_encoding     : byte;
          file_version      : byte;
          padding           : array[$07..$0f] of byte;
          e_type            : word;
          e_machine         : word;
          e_version         : longint;
          e_entry           : qword;            { entrypoint }
          e_phoff           : qword;            { program header offset }
          e_shoff           : qword;            { sections header offset }
          e_flags           : longint;
          e_ehsize          : word;             { elf header size in bytes }
          e_phentsize       : word;             { size of an entry in the program header array }
          e_phnum           : word;             { 0..e_phnum-1 of entrys }
          e_shentsize       : word;             { size of an entry in sections header array }
          e_shnum           : word;             { 0..e_shnum-1 of entrys }
          e_shstrndx        : word;             { index of string section header }
        end;
        telf64sechdr=packed record
          sh_name           : longint;
          sh_type           : longint;
          sh_flags          : qword;
          sh_addr           : qword;
          sh_offset         : qword;
          sh_size           : qword;
          sh_link           : longint;
          sh_info           : longint;
          sh_addralign      : qword;
          sh_entsize        : qword;
        end;
        telf64reloc=packed record
          address : qword;
          info    : qword; { bit 0-7: type, 8-31: symbol }
          addend  : qword;
        end;
        telf64symbol=packed record
          st_name  : longint;
          st_info  : byte; { bit 0-3: type, 4-7: bind }
          st_other : byte;
          st_shndx : word;
          st_value : qword;
          st_size  : qword;
        end;


{$ifdef cpu64bitaddr}
        telfheader = telf64header;
        telfreloc = telf64reloc;
        telfsymbol = telf64symbol;
        telfsechdr = telf64sechdr;
{$else cpu64bitaddr}
        telfheader = telf32header;
        telfreloc = telf32reloc;
        telfsymbol = telf32symbol;
        telfsechdr = telf32sechdr;
{$endif cpu64bitaddr}


      function MayBeSwapHeader(h : telf32header) : telf32header;
        begin
          result:=h;
          if source_info.endian<>target_info.endian then
            with h do
              begin
                result.e_type:=swapendian(e_type);
                result.e_machine:=swapendian(e_machine);
                result.e_version:=swapendian(e_version);
                result.e_entry:=swapendian(e_entry);
                result.e_phoff:=swapendian(e_phoff);
                result.e_shoff:=swapendian(e_shoff);
                result.e_flags:=swapendian(e_flags);
                result.e_ehsize:=swapendian(e_ehsize);
                result.e_phentsize:=swapendian(e_phentsize);
                result.e_phnum:=swapendian(e_phnum);
                result.e_shentsize:=swapendian(e_shentsize);
                result.e_shnum:=swapendian(e_shnum);
                result.e_shstrndx:=swapendian(e_shstrndx);
              end;
        end;


      function MayBeSwapHeader(h : telf64header) : telf64header;
        begin
          result:=h;
          if source_info.endian<>target_info.endian then
            with h do
              begin
                result.e_type:=swapendian(e_type);
                result.e_machine:=swapendian(e_machine);
                result.e_version:=swapendian(e_version);
                result.e_entry:=swapendian(e_entry);
                result.e_phoff:=swapendian(e_phoff);
                result.e_shoff:=swapendian(e_shoff);
                result.e_flags:=swapendian(e_flags);
                result.e_ehsize:=swapendian(e_ehsize);
                result.e_phentsize:=swapendian(e_phentsize);
                result.e_phnum:=swapendian(e_phnum);
                result.e_shentsize:=swapendian(e_shentsize);
                result.e_shnum:=swapendian(e_shnum);
                result.e_shstrndx:=swapendian(e_shstrndx);
              end;
        end;


      function MaybeSwapSecHeader(h : telf32sechdr) : telf32sechdr;
        begin
          result:=h;
          if source_info.endian<>target_info.endian then
            with h do
              begin
                result.sh_name:=swapendian(sh_name);
                result.sh_type:=swapendian(sh_type);
                result.sh_flags:=swapendian(sh_flags);
                result.sh_addr:=swapendian(sh_addr);
                result.sh_offset:=swapendian(sh_offset);
                result.sh_size:=swapendian(sh_size);
                result.sh_link:=swapendian(sh_link);
                result.sh_info:=swapendian(sh_info);
                result.sh_addralign:=swapendian(sh_addralign);
                result.sh_entsize:=swapendian(sh_entsize);
              end;
        end;


      function MaybeSwapSecHeader(h : telf64sechdr) : telf64sechdr;
        begin
          result:=h;
          if source_info.endian<>target_info.endian then
            with h do
              begin
                result.sh_name:=swapendian(sh_name);
                result.sh_type:=swapendian(sh_type);
                result.sh_flags:=swapendian(sh_flags);
                result.sh_addr:=swapendian(sh_addr);
                result.sh_offset:=swapendian(sh_offset);
                result.sh_size:=swapendian(sh_size);
                result.sh_link:=swapendian(sh_link);
                result.sh_info:=swapendian(sh_info);
                result.sh_addralign:=swapendian(sh_addralign);
                result.sh_entsize:=swapendian(sh_entsize);
              end;
        end;


      function MaybeSwapElfSymbol(h : telf32symbol) : telf32symbol;
        begin
          result:=h;
          if source_info.endian<>target_info.endian then
            with h do
              begin
                result.st_name:=swapendian(st_name);
                result.st_value:=swapendian(st_value);
                result.st_size:=swapendian(st_size);
                result.st_shndx:=swapendian(st_shndx);
              end;
        end;


      function MaybeSwapElfSymbol(h : telf64symbol) : telf64symbol;
        begin
          result:=h;
          if source_info.endian<>target_info.endian then
            with h do
              begin
                result.st_name:=swapendian(st_name);
                result.st_value:=swapendian(st_value);
                result.st_size:=swapendian(st_size);
                result.st_shndx:=swapendian(st_shndx);
              end;
        end;


      function MaybeSwapElfReloc(h : telf32reloc) : telf32reloc;
        begin
          result:=h;
          if source_info.endian<>target_info.endian then
            with h do
              begin
                result.address:=swapendian(address);
                result.info:=swapendian(info);
              end;
        end;


      function MaybeSwapElfReloc(h : telf64reloc) : telf64reloc;
        begin
          result:=h;
          if source_info.endian<>target_info.endian then
            with h do
              begin
                result.address:=swapendian(address);
                result.info:=swapendian(info);
              end;
        end;


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

    procedure encodesechdrflags(aoptions:TObjSectionOptions;out AshType:longint;out Ashflags:longint);
      begin
        { Section Type }
        AshType:=SHT_PROGBITS;
        if oso_strings in aoptions then
          AshType:=SHT_STRTAB
        else if not(oso_data in aoptions) then
          AshType:=SHT_NOBITS;
        { 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;
      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)
        else
          include(aoptions,oso_noload);
        if Ashflags and SHF_WRITE<>0 then
          include(aoptions,oso_write)
        else
          include(aoptions,oso_readonly);
      end;


{****************************************************************************
                               TSection
****************************************************************************}

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


    constructor TElfObjSection.create_ext(AList:TFPHashObjectList;const Aname:string;Ashtype,Ashflags,Ashlink,Ashinfo:longint;Aalign:shortint;Aentsize:longint);
      var
        aoptions : TObjSectionOptions;
      begin
        decodesechdrflags(Ashtype,Ashflags,aoptions);
        inherited create(AList,Aname,Aalign,aoptions);
        secshidx:=0;
        shstridx:=0;
        shtype:=AshType;
        shflags:=AshFlags;
        shlink:=Ashlink;
        shinfo:=Ashinfo;
        shentsize:=Aentsize;
      end;


    destructor TElfObjSection.destroy;
      begin
        inherited destroy;
      end;


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

    constructor TElfObjData.create(const n:string);
      begin
        inherited create(n);
        CObjSection:=TElfObjSection;
        { we need at least the following sections }
        createsection(sec_code);
        createsection(sec_data);
        createsection(sec_bss);
        if tf_section_threadvars in target_info.flags then
          createsection(sec_threadvar);
        if (tf_needs_dwarf_cfi in target_info.flags) and
           (af_supports_dwarf in target_asm.flags) then
             createsection(sec_debug_frame);
      end;


    destructor TElfObjData.destroy;
      begin
        inherited destroy;
      end;


    function TElfObjData.sectionname(atype:TAsmSectiontype;const aname:string;aorder:TAsmSectionOrder):string;
      const
        secnames : array[TAsmSectiontype] of string[length('__DATA, __datacoal_nt,coalesced')] = ('',
{$ifdef userodata}
          '.text','.data','.data','.rodata','.bss','.threadvar',
{$else userodata}
          '.text','.data','.data','.data','.bss','.threadvar',
{$endif userodata}
          '.pdata',
          '.text', { darwin stubs }
          '.stab','.stabstr',
          '.idata$2','.idata$4','.idata$5','.idata$6','.idata$7','.edata',
          '.eh_frame',
          '.debug_frame','.debug_info','.debug_line','.debug_abbrev',
          '.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'
        );
        secnames_pic : array[TAsmSectiontype] of string[length('__DATA, __datacoal_nt,coalesced')] = ('',
          '.text',
          '.data.rel',
          '.data.rel',
          '.data.rel',
          '.bss',
          '.threadvar',
          '.pdata',
          '', { stubs }
          '.stab',
          '.stabstr',
          '.idata$2','.idata$4','.idata$5','.idata$6','.idata$7','.edata',
          '.eh_frame',
          '.debug_frame','.debug_info','.debug_line','.debug_abbrev',
          '.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'
        );
      var
        sep : string[3];
        secname : string;
      begin
        if (cs_create_pic in current_settings.moduleswitches) and
           not(target_info.system in systems_darwin) then
          secname:=secnames_pic[atype]
        else
          secname:=secnames[atype];
        if (atype=sec_fpc) and (Copy(aname,1,3)='res') then
          begin
            result:=secname+'.'+aname;
            exit;
          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;


    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);
      var
        symaddr : longint;
      begin
        if CurrObjSec=nil then
          internalerror(200403292);
{$ifdef userodata}
        if CurrObjSec.sectype in [sec_rodata,sec_bss,sec_threadvar] then
          internalerror(200408252);
{$endif userodata}
        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}]) then
             begin
               { 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
                   CurrObjSec.addsectionreloc(CurrObjSec.Size,p.objsection,reltype);
                   inc(data,symaddr);
                 end;
             end
           else
             begin
               CurrObjSec.addsymreloc(CurrObjSec.Size,p,reltype);
{$ifndef x86_64}
               if reltype=RELOC_RELATIVE then
                 dec(data,len);
{$endif x86_64}
            end;
         end;
        CurrObjSec.write(data,len);
      end;


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

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


    destructor TElfObjectOutput.destroy;
      begin
        inherited destroy;
      end;


    procedure TElfObjectOutput.createrelocsection(s:TElfObjSection);
      var
        i    : longint;
        rel  : telfreloc;
        objreloc : TObjRelocation;
        relsym,
        reltyp   : longint;
        relocsect : TObjSection;
      begin
        with elf32data do
         begin
{$ifdef userodata}
           { rodata can't have relocations }
           if s.sectype=sec_rodata then
             begin
               if assigned(s.relocations.first) then
                 internalerror(200408251);
               exit;
             end;
{$endif userodata}
           { create the reloc section }
{$ifdef i386}
           relocsect:=TElfObjSection.create_ext(ObjSectionList,'.rel'+s.name,SHT_REL,0,symtabsect.secshidx,s.secshidx,4,sizeof(TElfReloc));
{$else i386}
           relocsect:=TElfObjSection.create_ext(ObjSectionList,'.rela'+s.name,SHT_RELA,0,symtabsect.secshidx,s.secshidx,4,sizeof(TElfReloc));
{$endif i386}
           { add the relocations }
           for i:=0 to s.Objrelocations.count-1 do
             begin
               objreloc:=TObjRelocation(s.Objrelocations[i]);
               fillchar(rel,sizeof(rel),0);
               rel.address:=objreloc.dataoffset;

               { when things settle down, we can create processor specific
                 derived classes }
               case objreloc.typ of
{$ifdef i386}
                 RELOC_RELATIVE :
                   reltyp:=R_386_PC32;
                 RELOC_ABSOLUTE :
                   reltyp:=R_386_32;
{$endif i386}
{$ifdef sparc}
                 RELOC_ABSOLUTE :
                   reltyp:=R_SPARC_32;
{$endif sparc}
{$ifdef x86_64}
                 RELOC_RELATIVE :
                   begin
                     reltyp:=R_X86_64_PC32;
                     { length of the relocated location is handled here }
                     rel.addend:=qword(-4);
                   end;
                 RELOC_ABSOLUTE :
                   reltyp:=R_X86_64_64;
                 RELOC_ABSOLUTE32 :
                   reltyp:=R_X86_64_32S;
                 RELOC_GOTPCREL :
                   begin
                     reltyp:=R_X86_64_GOTPCREL;
                     { length of the relocated location is handled here }
                     rel.addend:=qword(-4);
                   end;
                 RELOC_PLT32 :
                   begin
                     reltyp:=R_X86_64_PLT32;
                     { length of the relocated location is handled here }
                     rel.addend:=qword(-4);
                   end;
{$endif x86_64}
                 else
                   internalerror(200602261);
               end;

               { 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;
{$ifdef cpu64bitaddr}
               rel.info:=(qword(relsym) shl 32) or reltyp;
{$else cpu64bitaddr}
               rel.info:=(relsym shl 8) or reltyp;
{$endif cpu64bitaddr}
               { write reloc }
               relocsect.write(MaybeSwapElfReloc(rel),sizeof(rel));
             end;
         end;
      end;


    procedure TElfObjectOutput.write_internal_symbol(astridx:longint;ainfo:byte;ashndx:word);
      var
        elfsym : telfsymbol;
      begin
        fillchar(elfsym,sizeof(elfsym),0);
        elfsym.st_name:=astridx;
        elfsym.st_info:=ainfo;
        elfsym.st_shndx:=ashndx;
        inc(symidx);
        inc(localsyms);
        symtabsect.write(MaybeSwapElfSymbol(elfsym),sizeof(elfsym));
      end;


    procedure TElfObjectOutput.section_write_symbol(p:TObject;arg:pointer);
      begin
        TObjSection(p).secsymidx:=symidx;
        write_internal_symbol(TElfObjSection(p).shstridx,STT_SECTION,TElfObjSection(p).secshidx);
      end;


    procedure TElfObjectOutput.createsymtab;

        procedure WriteSym(objsym:TObjSymbol);
        var
          elfsym : telfsymbol;
        begin
          with elf32data do
            begin
              fillchar(elfsym,sizeof(elfsym),0);
              { symbolname, write the #0 separate to overcome 255+1 char not possible }
              elfsym.st_name:=strtabsect.Size;
              strtabsect.writestr(objsym.name);
              strtabsect.writestr(#0);
              elfsym.st_size:=objsym.size;
              case objsym.bind of
                AB_LOCAL :
                  begin
                    elfsym.st_value:=objsym.address;
                    elfsym.st_info:=STB_LOCAL shl 4;
                    inc(localsyms);
                  end;
                AB_COMMON :
                  begin
                    elfsym.st_value:=$10;
                    elfsym.st_info:=STB_GLOBAL shl 4;
                  end;
                AB_EXTERNAL :
                  elfsym.st_info:=STB_GLOBAL shl 4;
                AB_GLOBAL :
                  begin
                    elfsym.st_value:=objsym.address;
                    elfsym.st_info:=STB_GLOBAL shl 4;
                  end;
              end;
              if (objsym.bind<>AB_EXTERNAL) {and
                  not(assigned(objsym.objsection) and
                  not(oso_data in objsym.objsection.secoptions))} then
                begin
                  case objsym.typ of
                    AT_FUNCTION :
                      elfsym.st_info:=elfsym.st_info or STT_FUNC;
                    AT_DATA :
                      elfsym.st_info:=elfsym.st_info or STT_OBJECT;
                  end;
                end;
              if objsym.bind=AB_COMMON then
                elfsym.st_shndx:=SHN_COMMON
              else
                begin
                  if assigned(objsym.objsection) then
                    elfsym.st_shndx:=TElfObjSection(objsym.objsection).secshidx
                  else
                    elfsym.st_shndx:=SHN_UNDEF;
                end;
              objsym.symidx:=symidx;
              inc(symidx);
              symtabsect.write(MaybeSwapElfSymbol(elfsym),sizeof(elfsym));
            end;
        end;

      var
        i      : longint;
        objsym : TObjSymbol;
      begin
        with elf32data do
         begin
           symidx:=0;
           localsyms:=0;
           { empty entry }
           write_internal_symbol(0,0,0);
           { filename entry }
           write_internal_symbol(1,STT_FILE,SHN_ABS);
           { section }
           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
                 WriteSym(objsym);
             end;
           { Global Symbols }
           for i:=0 to ObjSymbolList.Count-1 do
             begin
               objsym:=TObjSymbol(ObjSymbolList[i]);
               if (objsym.bind<>AB_LOCAL) then
                 WriteSym(objsym);
             end;
           { update the .symtab section header }
           symtabsect.shlink:=strtabsect.secshidx;
           symtabsect.shinfo:=localsyms;
         end;
      end;


    procedure TElfObjectOutput.section_write_sh_string(p:TObject;arg:pointer);
      begin
        TElfObjSection(p).shstridx:=shstrtabsect.writestr(TObjSection(p).name+#0);
      end;


    procedure TElfObjectOutput.createshstrtab;
      begin
        with elf32data do
         begin
           shstrtabsect.writestr(#0);
           ObjSectionList.ForEachCall(@section_write_sh_string,nil);
         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;
        writer.write(MaybeSwapSecHeader(sechdr),sizeof(sechdr));
      end;


    procedure TElfObjectOutput.writesectiondata(s:TElfObjSection);
      begin
        FWriter.writezeros(s.dataalignbytes);
        if s.Datapos<>FWriter.ObjSize then
          internalerror(200604031);
        FWriter.writearray(s.data);
      end;


    procedure TElfObjectOutput.section_count_sections(p:TObject;arg:pointer);
      begin
        TElfObjSection(p).secshidx:=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));
      end;


    procedure TElfObjectOutput.section_set_datapos(p:TObject;arg:pointer);
      begin
        TObjSection(p).setdatapos(paword(arg)^);
      end;


    procedure TElfObjectOutput.section_write_data(p:TObject;arg:pointer);
      begin
        if (oso_data in TObjSection(p).secoptions) then
          begin
            if TObjSection(p).data=nil then
              internalerror(200403073);
            writesectiondata(TElfObjSection(p));
          end;
      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   : aint;
        nsections : word;
      begin
        result:=false;
        elf32data:=TElfObjData(data);
        with elf32data do
         begin
           { default sections }
           symtabsect:=TElfObjSection.create_ext(ObjSectionList,'.symtab',SHT_SYMTAB,0,0,0,4,sizeof(telfsymbol));
           strtabsect:=TElfObjSection.create_ext(ObjSectionList,'.strtab',SHT_STRTAB,0,0,0,1,0);
           shstrtabsect:=TElfObjSection.create_ext(ObjSectionList,'.shstrtab',SHT_STRTAB,0,0,0,1,0);
           { "no executable stack" marker for Linux }
           if (target_info.system in system_linux) and
              not(cs_executable_stack in current_settings.moduleswitches) then
             TElfObjSection.create_ext(ObjSectionList,'.note.GNU-stack',SHT_PROGBITS,0,0,0,1,0);
           { insert the empty and filename as first in strtab }
           strtabsect.writestr(#0);
           strtabsect.writestr(ExtractFileName(current_module.mainsource^)+#0);
           { 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;
           { Create the relocation sections, this needs valid secidx and symidx }
           ObjSectionList.ForEachCall(@section_create_relocsec,nil);
           { recalc nsections to incude the reloc sections }
           nsections:=1;
           ObjSectionList.ForEachCall(@section_count_sections,@nsections);
           { create .shstrtab }
           createshstrtab;

           { Calculate the filepositions }
           datapos:=$40; { elfheader + alignment }
           { section data }
           ObjSectionList.ForEachCall(@section_set_datapos,@datapos);
           { section headers }
           shoffset:=datapos;
           inc(datapos,(nsections+1)*sizeof(telfsechdr));

           { Write ELF Header }
           fillchar(header,sizeof(header),0);
           header.magic0123:=$464c457f; { = #127'ELF' }
{$ifdef cpu64bitaddr}
           header.file_class:=2;
{$else cpu64bitaddr}
           header.file_class:=1;
{$endif cpu64bitaddr}
           if target_info.endian=endian_big then
             header.data_encoding:=2
           else
           header.data_encoding:=1;

           header.file_version:=1;
           header.e_type:=1;
{$ifdef sparc}
           header.e_machine:=2;
{$endif sparc}
{$ifdef i386}
           header.e_machine:=3;
{$endif i386}
{$ifdef m68k}
           header.e_machine:=4;
{$endif m68k}
{$ifdef powerpc}
           header.e_machine:=20;
{$endif powerpc}
{$ifdef arm}
           header.e_machine:=40;
           if (current_settings.fputype=cpu_soft) then
             header.e_flags:=$600;
{$endif arm}
{$ifdef x86_64}
           header.e_machine:=62;
{$endif x86_64}
           header.e_version:=1;
           header.e_shoff:=shoffset;
           header.e_shstrndx:=shstrtabsect.secshidx;

           header.e_shnum:=nsections;
           header.e_ehsize:=sizeof(telfheader);
           header.e_shentsize:=sizeof(telfsechdr);
           writer.write(MaybeSwapHeader(header),sizeof(header));
           writer.writezeros($40-sizeof(header)); { align }
           { Sections }
           ObjSectionList.ForEachCall(@section_write_data,nil);
           { 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(smart:boolean);
      begin
        inherited Create(smart);
        CObjOutput:=TElfObjectOutput;
      end;


{*****************************************************************************
                                  Initialize
*****************************************************************************}

{$ifdef i386}
     const
       as_i386_elf32_info : tasminfo =
          (
            id     : as_i386_elf32;
            idtxt  : 'ELF';
            asmbin : '';
            asmcmd : '';
            supported_targets : [system_i386_linux,system_i386_beos,system_i386_freebsd,system_i386_haiku,system_i386_Netware,system_i386_netwlibc];
            flags : [af_outputbinary,af_smartlink_sections,af_supports_dwarf];
            labelprefix : '.L';
            comment : '';
          );
{$endif i386}
{$ifdef x86_64}
     const
       as_x86_64_elf64_info : tasminfo =
          (
            id     : as_x86_64_elf64;
            idtxt  : 'ELF';
            asmbin : '';
            asmcmd : '';
            supported_targets : [system_x86_64_linux];
            flags : [af_outputbinary,af_smartlink_sections,af_supports_dwarf];
            labelprefix : '.L';
            comment : '';
          );
{$endif x86_64}
{$ifdef sparc}
     const
       as_sparc_elf32_info : tasminfo =
          (
            id     : as_sparc_elf32;
            idtxt  : 'ELF';
            asmbin : '';
            asmcmd : '';
            supported_targets : [];
//            flags : [af_outputbinary,af_smartlink_sections];
            flags : [af_outputbinary,af_supports_dwarf];
            labelprefix : '.L';
            comment : '';
          );
{$endif sparc}


initialization
{$ifdef i386}
  RegisterAssembler(as_i386_elf32_info,TElfAssembler);
{$endif i386}
{$ifdef sparc}
  RegisterAssembler(as_sparc_elf32_info,TElfAssembler);
{$endif sparc}
{$ifdef x86_64}
  RegisterAssembler(as_x86_64_elf64_info,TElfAssembler);
{$endif x86_64}
end.