freepascal.compiler/compiler/ogomf.pas

{
    Copyright (c) 2015 by Nikolay Nikolov

    Contains the binary Relocatable Object Module Format (OMF) reader and writer
    This is the object format used on the i8086-msdos platform.

    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 ogomf;

{$i fpcdefs.inc}

interface

    uses
       { common }
       cclasses,globtype,
       { target }
       systems,
       { assembler }
       cpuinfo,cpubase,aasmbase,assemble,link,
       { OMF definitions }
       omfbase,
       { output }
       ogbase,
       owbase;

    type

      { TOmfObjSymbol }

      TOmfObjSymbol = class(TObjSymbol)
      public
        { string representation for the linker map file }
        function AddressStr(AImageBase: qword): string;override;
      end;

      { TOmfRelocation }

      TOmfRelocation = class(TObjRelocation)
      private
        FFrameGroup: string;
        FOmfFixup: TOmfSubRecord_FIXUP;
        function GetGroupIndex(const groupname: string): Integer;
      public
        destructor Destroy; override;

        procedure BuildOmfFixup;

        property FrameGroup: string read FFrameGroup write FFrameGroup;
        property OmfFixup: TOmfSubRecord_FIXUP read FOmfFixup;
      end;

      TMZExeUnifiedLogicalSegment=class;

      { TOmfObjSection }

      TOmfObjSection = class(TObjSection)
      private
        FClassName: string;
        FOverlayName: string;
        FCombination: TOmfSegmentCombination;
        FUse: TOmfSegmentUse;
        FPrimaryGroup: string;
        FSortOrder: Integer;
        FMZExeUnifiedLogicalSegment: TMZExeUnifiedLogicalSegment;
        FLinNumEntries: TOmfSubRecord_LINNUM_MsLink_LineNumberList;
        function GetOmfAlignment: TOmfSegmentAlignment;
      public
        constructor create(AList:TFPHashObjectList;const Aname:string;Aalign:longint;Aoptions:TObjSectionOptions);override;
        destructor destroy;override;
        function MemPosStr(AImageBase: qword): string;override;
        property ClassName: string read FClassName;
        property OverlayName: string read FOverlayName;
        property OmfAlignment: TOmfSegmentAlignment read GetOmfAlignment;
        property Combination: TOmfSegmentCombination read FCombination;
        property Use: TOmfSegmentUse read FUse;
        property PrimaryGroup: string read FPrimaryGroup;
        property SortOrder: Integer read FSortOrder write FSortOrder;
        property MZExeUnifiedLogicalSegment: TMZExeUnifiedLogicalSegment read FMZExeUnifiedLogicalSegment write FMZExeUnifiedLogicalSegment;
        property LinNumEntries: TOmfSubRecord_LINNUM_MsLink_LineNumberList read FLinNumEntries;
      end;

      { TOmfObjData }

      TOmfObjData = class(TObjData)
      private
        FMainSource: TPathStr;
        class function CodeSectionName(const aname:string): string;
      public
        constructor create(const n:string);override;
        function sectiontype2options(atype:TAsmSectiontype):TObjSectionOptions;override;
        function sectiontype2align(atype:TAsmSectiontype):longint;override;
        function sectiontype2class(atype:TAsmSectiontype):string;
        function sectionname(atype:TAsmSectiontype;const aname:string;aorder:TAsmSectionOrder):string;override;
        function createsection(atype:TAsmSectionType;const aname:string='';aorder:TAsmSectionOrder=secorder_default):TObjSection;override;
        function reffardatasection:TObjSection;
        procedure writeReloc(Data:TRelocDataInt;len:aword;p:TObjSymbol;Reloctype:TObjRelocationType);override;
        property MainSource: TPathStr read FMainSource;
      end;

      { TOmfObjOutput }

      TOmfObjOutput = class(tObjOutput)
      private
        FLNames: TOmfOrderedNameCollection;
        FSegments: TFPHashObjectList;
        FGroups: TFPHashObjectList;
        procedure AddSegment(const name,segclass,ovlname: string;
          Alignment: TOmfSegmentAlignment; Combination: TOmfSegmentCombination;
          Use: TOmfSegmentUse; Size: TObjSectionOfs);
        procedure AddGroup(const groupname: string; seglist: array of const);
        procedure AddGroup(const groupname: string; seglist: TSegmentList);
        procedure WriteSections(Data:TObjData);
        procedure WriteSectionContentAndFixups(sec: TObjSection);
        procedure WriteLinNumRecords(sec: TOmfObjSection);

        procedure section_count_sections(p:TObject;arg:pointer);
        procedure WritePUBDEFs(Data: TObjData);
        procedure WriteEXTDEFs(Data: TObjData);

        property LNames: TOmfOrderedNameCollection read FLNames;
        property Segments: TFPHashObjectList read FSegments;
        property Groups: TFPHashObjectList read FGroups;
      protected
        function writeData(Data:TObjData):boolean;override;
      public
        constructor create(AWriter:TObjectWriter);override;
        destructor Destroy;override;
        procedure WriteDllImport(const dllname,afuncname,mangledname:string;ordnr:longint;isvar:boolean);
      end;

      { TOmfObjInput }

      TOmfObjInput = class(TObjInput)
      private
        FLNames: TOmfOrderedNameCollection;
        FExtDefs: TFPHashObjectList;
        FPubDefs: TFPHashObjectList;
        FFixupThreads: TOmfThreads;
        FRawRecord: TOmfRawRecord;
        FCaseSensitiveSegments: Boolean;
        FCaseSensitiveSymbols: Boolean;

        function PeekNextRecordType: Byte;

        function ReadLNames(RawRec: TOmfRawRecord): Boolean;
        function ReadSegDef(RawRec: TOmfRawRecord; objdata:TObjData): Boolean;
        function ReadGrpDef(RawRec: TOmfRawRecord; objdata:TObjData): Boolean;
        function ReadExtDef(RawRec: TOmfRawRecord; objdata:TObjData): Boolean;
        function ReadPubDef(RawRec: TOmfRawRecord; objdata:TObjData): Boolean;
        function ReadModEnd(RawRec: TOmfRawRecord; objdata:TObjData): Boolean;
        function ReadLeOrLiDataAndFixups(RawRec: TOmfRawRecord; objdata:TObjData): Boolean;
        function ImportOmfFixup(objdata: TObjData; objsec: TOmfObjSection; Fixup: TOmfSubRecord_FIXUP): Boolean;

        property LNames: TOmfOrderedNameCollection read FLNames;
        property ExtDefs: TFPHashObjectList read FExtDefs;
        property PubDefs: TFPHashObjectList read FPubDefs;

        { Specifies whether we're case sensitive in regards to segment, class, overlay and group names. }
        property CaseSensitiveSegments: Boolean read FCaseSensitiveSegments write FCaseSensitiveSegments;
        { Specifies whether symbol names (in EXTDEF and PUBDEF records) are case sensitive. }
        property CaseSensitiveSymbols: Boolean read FCaseSensitiveSymbols write FCaseSensitiveSymbols;
      public
        constructor create;override;
        destructor destroy;override;
        class function CanReadObjData(AReader:TObjectreader):boolean;override;
        function ReadObjData(AReader:TObjectreader;out objdata:TObjData):boolean;override;
      end;

      { TMZExeRelocation }

      TMZExeRelocation = record
        offset: Word;
        segment: Word;
      end;
      TMZExeRelocations = array of TMZExeRelocation;
      TMZExeExtraHeaderData = array of Byte;

      { TMZExeHeader }

      TMZExeHeader = class
      private
        FChecksum: Word;
        FExtraHeaderData: TMZExeExtraHeaderData;
        FHeaderSizeAlignment: Integer;
        FInitialCS: Word;
        FInitialIP: Word;
        FInitialSP: Word;
        FInitialSS: Word;
        FLoadableImageSize: DWord;
        FMaxExtraParagraphs: Word;
        FMinExtraParagraphs: Word;
        FOverlayNumber: Word;
        FRelocations: TMZExeRelocations;
        procedure SetHeaderSizeAlignment(AValue: Integer);
      public
        constructor Create;
        procedure WriteTo(aWriter: TObjectWriter);
        procedure AddRelocation(aSegment,aOffset: Word);
        property HeaderSizeAlignment: Integer read FHeaderSizeAlignment write SetHeaderSizeAlignment; {default=16, must be multiple of 16}
        property Relocations: TMZExeRelocations read FRelocations write FRelocations;
        property ExtraHeaderData: TMZExeExtraHeaderData read FExtraHeaderData write FExtraHeaderData;
        property LoadableImageSize: DWord read FLoadableImageSize write FLoadableImageSize;
        property MinExtraParagraphs: Word read FMinExtraParagraphs write FMinExtraParagraphs;
        property MaxExtraParagraphs: Word read FMaxExtraParagraphs write FMaxExtraParagraphs;
        property InitialSS: Word read FInitialSS write FInitialSS;
        property InitialSP: Word read FInitialSP write FInitialSP;
        property Checksum: Word read FChecksum write FChecksum;
        property InitialIP: Word read FInitialIP write FInitialIP;
        property InitialCS: Word read FInitialCS write FInitialCS;
        property OverlayNumber: Word read FOverlayNumber write FOverlayNumber;
      end;

      { TMZExeSection }

      TMZExeSection=class(TExeSection)
      public
        procedure AddObjSection(objsec:TObjSection;ignoreprops:boolean=false);override;
      end;

      { TMZExeUnifiedLogicalSegment }

      TMZExeUnifiedLogicalSegment=class(TFPHashObject)
      private
        FObjSectionList: TFPObjectList;
        FSegName: TSymStr;
        FSegClass: TSymStr;
        FPrimaryGroup: string;
      public
        Size,
        MemPos,
        MemBasePos: qword;
        IsStack: Boolean;
        constructor create(HashObjectList:TFPHashObjectList;const s:TSymStr);
        destructor destroy;override;
        procedure AddObjSection(ObjSec: TOmfObjSection);
        procedure CalcMemPos;
        function MemPosStr:string;
        property ObjSectionList: TFPObjectList read FObjSectionList;
        property SegName: TSymStr read FSegName;
        property SegClass: TSymStr read FSegClass;
        property PrimaryGroup: string read FPrimaryGroup write FPrimaryGroup;
      end;

      { TMZExeUnifiedLogicalGroup }

      TMZExeUnifiedLogicalGroup=class(TFPHashObject)
      private
        FSegmentList: TFPHashObjectList;
      public
        Size,
        MemPos: qword;
        constructor create(HashObjectList:TFPHashObjectList;const s:TSymStr);
        destructor destroy;override;
        procedure CalcMemPos;
        function MemPosStr:string;
        procedure AddSegment(UniSeg: TMZExeUnifiedLogicalSegment);
        property SegmentList: TFPHashObjectList read FSegmentList;
      end;

      { TMZExeOutput }

      TMZExeOutput = class(TExeOutput)
      private
        FMZFlatContentSection: TMZExeSection;
        FExeUnifiedLogicalSegments: TFPHashObjectList;
        FExeUnifiedLogicalGroups: TFPHashObjectList;
        FHeader: TMZExeHeader;
        function GetMZFlatContentSection: TMZExeSection;
        procedure CalcExeUnifiedLogicalSegments;
        procedure CalcExeGroups;
        procedure CalcSegments_MemBasePos;
        procedure WriteMap_SegmentsAndGroups;
        procedure WriteMap_HeaderData;
        function FindStackSegment: TMZExeUnifiedLogicalSegment;
        procedure FillLoadableImageSize;
        procedure FillMinExtraParagraphs;
        procedure FillMaxExtraParagraphs;
        procedure FillStartAddress;
        procedure FillStackAddress;
        procedure FillHeaderData;
        function writeExe:boolean;
        function writeCom:boolean;
        function writeDebugElf:boolean;
        property ExeUnifiedLogicalSegments: TFPHashObjectList read FExeUnifiedLogicalSegments;
        property ExeUnifiedLogicalGroups: TFPHashObjectList read FExeUnifiedLogicalGroups;
        property Header: TMZExeHeader read FHeader;
      protected
        procedure Load_Symbol(const aname:string);override;
        procedure DoRelocationFixup(objsec:TObjSection);override;
        procedure Order_ObjSectionList(ObjSectionList : TFPObjectList;const aPattern:string);override;
        procedure MemPos_EndExeSection;override;
        function writeData:boolean;override;
      public
        constructor create;override;
        destructor destroy;override;
        property MZFlatContentSection: TMZExeSection read GetMZFlatContentSection;
      end;

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

implementation

    uses
       SysUtils,
       cutils,verbose,globals,
       fmodule,aasmtai,aasmdata,
       ogmap,owomflib,elfbase,
       version
       ;

    const win16stub : array[0..255] of byte=(
      $4d,$5a,$00,$01,$01,$00,$00,$00,$08,$00,$10,$00,$ff,$ff,$08,$00,
      $00,$01,$00,$00,$00,$00,$00,$00,$40,$00,$00,$00,$00,$00,$00,$00,
      $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,
      $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$01,$00,$00,
      $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,
      $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,
      $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,
      $00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,$00,
      $ba,$10,$00,$0e,$1f,$b4,$09,$cd,$21,$b8,$01,$4c,$cd,$21,$90,$90,
      $54,$68,$69,$73,$20,$70,$72,$6f,$67,$72,$61,$6d,$20,$72,$65,$71,
      $75,$69,$72,$65,$73,$20,$4d,$69,$63,$72,$6f,$73,$6f,$66,$74,$20,
      $57,$69,$6e,$64,$6f,$77,$73,$2e,$0d,$0a,$24,$20,$20,$20,$20,$20,
      $20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,
      $20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,
      $20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,
      $20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20,$20);

{****************************************************************************
                                TOmfObjSymbol
****************************************************************************}

    function TOmfObjSymbol.AddressStr(AImageBase: qword): string;
      var
        base: qword;
      begin
        if assigned(TOmfObjSection(objsection).MZExeUnifiedLogicalSegment) then
          base:=TOmfObjSection(objsection).MZExeUnifiedLogicalSegment.MemBasePos
        else
          base:=(address shr 4) shl 4;
        Result:=HexStr(base shr 4,4)+':'+HexStr(address-base,4);
      end;

{****************************************************************************
                                TOmfRelocation
****************************************************************************}

    function TOmfRelocation.GetGroupIndex(const groupname: string): Integer;
      begin
        if groupname='DGROUP' then
          Result:=1
        else
          internalerror(2014040703);
      end;

    destructor TOmfRelocation.Destroy;
      begin
        FOmfFixup.Free;
        inherited Destroy;
      end;

    procedure TOmfRelocation.BuildOmfFixup;
      begin
        FreeAndNil(FOmfFixup);
        FOmfFixup:=TOmfSubRecord_FIXUP.Create;
        if ObjSection<>nil then
          begin
            FOmfFixup.LocationOffset:=DataOffset;
            if typ in [RELOC_ABSOLUTE16,RELOC_RELATIVE16] then
              FOmfFixup.LocationType:=fltOffset
            else if typ in [RELOC_ABSOLUTE32,RELOC_RELATIVE32] then
              FOmfFixup.LocationType:=fltOffset32
            else if typ in [RELOC_SEG,RELOC_SEGREL] then
              FOmfFixup.LocationType:=fltBase
            else
              internalerror(2015041501);
            FOmfFixup.FrameDeterminedByThread:=False;
            FOmfFixup.TargetDeterminedByThread:=False;
            if typ in [RELOC_ABSOLUTE16,RELOC_ABSOLUTE32,RELOC_SEG] then
              FOmfFixup.Mode:=fmSegmentRelative
            else if typ in [RELOC_RELATIVE16,RELOC_RELATIVE32,RELOC_SEGREL] then
              FOmfFixup.Mode:=fmSelfRelative
            else
              internalerror(2015041401);
            if typ in [RELOC_ABSOLUTE16,RELOC_ABSOLUTE32,RELOC_RELATIVE16,RELOC_RELATIVE32] then
              begin
                FOmfFixup.TargetMethod:=ftmSegmentIndexNoDisp;
                FOmfFixup.TargetDatum:=ObjSection.Index;
                if TOmfObjSection(ObjSection).PrimaryGroup<>'' then
                  begin
                    FOmfFixup.FrameMethod:=ffmGroupIndex;
                    FOmfFixup.FrameDatum:=GetGroupIndex(TOmfObjSection(ObjSection).PrimaryGroup);
                  end
                else
                  FOmfFixup.FrameMethod:=ffmTarget;
              end
            else
              begin
                FOmfFixup.FrameMethod:=ffmTarget;
                if TOmfObjSection(ObjSection).PrimaryGroup<>'' then
                  begin
                    FOmfFixup.TargetMethod:=ftmGroupIndexNoDisp;
                    FOmfFixup.TargetDatum:=GetGroupIndex(TOmfObjSection(ObjSection).PrimaryGroup);
                  end
                else
                  begin
                    FOmfFixup.TargetMethod:=ftmSegmentIndexNoDisp;
                    FOmfFixup.TargetDatum:=ObjSection.Index;
                  end;
              end;
          end
        else if symbol<>nil then
          begin
            FOmfFixup.LocationOffset:=DataOffset;
            if typ in [RELOC_ABSOLUTE16,RELOC_RELATIVE16] then
              FOmfFixup.LocationType:=fltOffset
            else if typ in [RELOC_ABSOLUTE32,RELOC_RELATIVE32] then
              FOmfFixup.LocationType:=fltOffset32
            else if typ in [RELOC_SEG,RELOC_SEGREL] then
              FOmfFixup.LocationType:=fltBase
            else
              internalerror(2015041501);
            FOmfFixup.FrameDeterminedByThread:=False;
            FOmfFixup.TargetDeterminedByThread:=False;
            if typ in [RELOC_ABSOLUTE16,RELOC_ABSOLUTE32,RELOC_SEG] then
              FOmfFixup.Mode:=fmSegmentRelative
            else if typ in [RELOC_RELATIVE16,RELOC_RELATIVE32,RELOC_SEGREL] then
              FOmfFixup.Mode:=fmSelfRelative
            else
              internalerror(2015041401);
            FOmfFixup.TargetMethod:=ftmExternalIndexNoDisp;
            FOmfFixup.TargetDatum:=symbol.symidx;
            FOmfFixup.FrameMethod:=ffmTarget;
          end
        else if group<>nil then
          begin
            FOmfFixup.LocationOffset:=DataOffset;
            if typ in [RELOC_ABSOLUTE16,RELOC_RELATIVE16] then
              FOmfFixup.LocationType:=fltOffset
            else if typ in [RELOC_ABSOLUTE32,RELOC_RELATIVE32] then
              FOmfFixup.LocationType:=fltOffset32
            else if typ in [RELOC_SEG,RELOC_SEGREL] then
              FOmfFixup.LocationType:=fltBase
            else
              internalerror(2015041501);
            FOmfFixup.FrameDeterminedByThread:=False;
            FOmfFixup.TargetDeterminedByThread:=False;
            if typ in [RELOC_ABSOLUTE16,RELOC_ABSOLUTE32,RELOC_SEG] then
              FOmfFixup.Mode:=fmSegmentRelative
            else if typ in [RELOC_RELATIVE16,RELOC_RELATIVE32,RELOC_SEGREL] then
              FOmfFixup.Mode:=fmSelfRelative
            else
              internalerror(2015041401);
            FOmfFixup.FrameMethod:=ffmTarget;
            FOmfFixup.TargetMethod:=ftmGroupIndexNoDisp;
            FOmfFixup.TargetDatum:=GetGroupIndex(group.Name);
          end
        else
         internalerror(2015040702);
      end;

{****************************************************************************
                                TOmfObjSection
****************************************************************************}

    function TOmfObjSection.GetOmfAlignment: TOmfSegmentAlignment;
      begin
        case SecAlign of
          1:
            result:=saRelocatableByteAligned;
          2:
            result:=saRelocatableWordAligned;
          4:
            result:=saRelocatableDWordAligned;
          16:
            result:=saRelocatableParaAligned;
          256:
            result:=saRelocatablePageAligned;
          4096:
            result:=saNotSupported;
          else
            internalerror(2015041504);
        end;
      end;

    constructor TOmfObjSection.create(AList: TFPHashObjectList;
          const Aname: string; Aalign: longint; Aoptions: TObjSectionOptions);
      begin
        inherited create(AList, Aname, Aalign, Aoptions);
        FCombination:=scPublic;
        FUse:=suUse16;
        FLinNumEntries:=TOmfSubRecord_LINNUM_MsLink_LineNumberList.Create;
      end;

    destructor TOmfObjSection.destroy;
      begin
        FLinNumEntries.Free;
        inherited destroy;
      end;

    function TOmfObjSection.MemPosStr(AImageBase: qword): string;
      begin
        Result:=HexStr(MZExeUnifiedLogicalSegment.MemBasePos shr 4,4)+':'+
          HexStr(MemPos-MZExeUnifiedLogicalSegment.MemBasePos,4);
      end;

{****************************************************************************
                                TOmfObjData
****************************************************************************}

    class function TOmfObjData.CodeSectionName(const aname: string): string;
      begin
{$ifdef i8086}
        if current_settings.x86memorymodel in x86_far_code_models then
          begin
            if cs_huge_code in current_settings.moduleswitches then
              result:=aname + '_TEXT'
            else
              result:=current_module.modulename^ + '_TEXT';
          end
        else
{$endif}
          result:='_TEXT';
      end;

    constructor TOmfObjData.create(const n: string);
      begin
        inherited create(n);
        CObjSymbol:=TOmfObjSymbol;
        CObjSection:=TOmfObjSection;
        createsectiongroup('DGROUP');
        FMainSource:=current_module.mainsource;
      end;

    function TOmfObjData.sectiontype2options(atype: TAsmSectiontype): TObjSectionOptions;
      begin
        Result:=inherited sectiontype2options(atype);
        { in the huge memory model, BSS data is actually written in the regular
          FAR_DATA segment of the module }
        if sectiontype2class(atype)='FAR_DATA' then
          Result:=Result+[oso_data,oso_sparse_data];
      end;

    function TOmfObjData.sectiontype2align(atype: TAsmSectiontype): longint;
      begin
        Result:=omf_sectiontype2align(atype);
      end;

    function TOmfObjData.sectiontype2class(atype: TAsmSectiontype): string;
      begin
        Result:=omf_segclass(atype);
      end;

    function TOmfObjData.sectionname(atype:TAsmSectiontype;const aname:string;aorder:TAsmSectionOrder):string;
      var
        sep : string[3];
        secname : string;
      begin
        if (atype=sec_user) then
          Result:=aname
        else
          begin
            if omf_secnames[atype]=omf_secnames[sec_code] then
              secname:=CodeSectionName(aname)
            else if omf_segclass(atype)='FAR_DATA' then
              secname:=current_module.modulename^ + '_DATA'
            else
              secname:=omf_secnames[atype];
            if create_smartlink_sections and (aname<>'') then
              begin
                case aorder of
                  secorder_begin :
                    sep:='.b_';
                  secorder_end :
                    sep:='.z_';
                  else
                    sep:='.n_';
                end;
                result:=UpCase(secname+sep+aname);
              end
            else
              result:=secname;
          end;
      end;

    function TOmfObjData.createsection(atype: TAsmSectionType; const aname: string; aorder: TAsmSectionOrder): TObjSection;
      begin
        Result:=inherited createsection(atype, aname, aorder);
        TOmfObjSection(Result).FClassName:=sectiontype2class(atype);
        if atype=sec_stack then
          TOmfObjSection(Result).FCombination:=scStack
        else if atype in [sec_debug_frame,sec_debug_info,sec_debug_line,sec_debug_abbrev,sec_debug_aranges,sec_debug_ranges] then
          begin
            TOmfObjSection(Result).FUse:=suUse32;
            TOmfObjSection(Result).SizeLimit:=high(longword);
          end;
        if section_belongs_to_dgroup(atype) then
          TOmfObjSection(Result).FPrimaryGroup:='DGROUP';
      end;

    function TOmfObjData.reffardatasection: TObjSection;
      var
        secname: string;
      begin
        secname:=current_module.modulename^ + '_DATA';

        result:=TObjSection(ObjSectionList.Find(secname));
        if not assigned(result) then
          begin
            result:=CObjSection.create(ObjSectionList,secname,2,[oso_Data,oso_load,oso_write]);
            result.ObjData:=self;
            TOmfObjSection(Result).FClassName:='FAR_DATA';
          end;
      end;

    procedure TOmfObjData.writeReloc(Data:TRelocDataInt;len:aword;p:TObjSymbol;Reloctype:TObjRelocationType);
      var
        objreloc: TOmfRelocation;
        symaddr: AWord;
      begin
        { RELOC_FARPTR = RELOC_ABSOLUTE16+RELOC_SEG }
        if Reloctype=RELOC_FARPTR then
          begin
            if len<>4 then
              internalerror(2015041502);
            writeReloc(Data,2,p,RELOC_ABSOLUTE16);
            writeReloc(0,2,p,RELOC_SEG);
            exit;
          end
        { RELOC_FARPTR48 = RELOC_ABSOLUTE16+RELOC_SEG }
        else if Reloctype=RELOC_FARPTR48 then
          begin
            if len<>6 then
              internalerror(2015041502);
            writeReloc(Data,4,p,RELOC_ABSOLUTE32);
            writeReloc(0,2,p,RELOC_SEG);
            exit;
          end;

        if CurrObjSec=nil then
          internalerror(200403072);
        objreloc:=nil;
        if Reloctype in [RELOC_FARDATASEG,RELOC_FARDATASEGREL] then
          begin
            if Reloctype=RELOC_FARDATASEG then
              objreloc:=TOmfRelocation.CreateSection(CurrObjSec.Size,reffardatasection,RELOC_SEG)
            else
              objreloc:=TOmfRelocation.CreateSection(CurrObjSec.Size,reffardatasection,RELOC_SEGREL);
            CurrObjSec.ObjRelocations.Add(objreloc);
          end
        else if assigned(p) then
          begin
            { real address of the symbol }
            symaddr:=p.address;

            if p.bind=AB_EXTERNAL then
              begin
                objreloc:=TOmfRelocation.CreateSymbol(CurrObjSec.Size,p,Reloctype);
                CurrObjSec.ObjRelocations.Add(objreloc);
              end
            { relative relocations within the same section can be calculated directly,
              without the need to emit a relocation entry }
            else if (p.objsection=CurrObjSec) and
                    (p.bind<>AB_COMMON) and
                    (Reloctype=RELOC_RELATIVE) then
              begin
                data:=data+symaddr-len-CurrObjSec.Size;
              end
            else
              begin
                objreloc:=TOmfRelocation.CreateSection(CurrObjSec.Size,p.objsection,Reloctype);
                CurrObjSec.ObjRelocations.Add(objreloc);
                if not (Reloctype in [RELOC_SEG,RELOC_SEGREL]) then
                  inc(data,symaddr);
              end;
          end
        else if Reloctype in [RELOC_DGROUP,RELOC_DGROUPREL] then
            begin
              if Reloctype=RELOC_DGROUP then
                objreloc:=TOmfRelocation.CreateGroup(CurrObjSec.Size,TObjSectionGroup(GroupsList.Find('DGROUP')),RELOC_SEG)
              else
                objreloc:=TOmfRelocation.CreateGroup(CurrObjSec.Size,TObjSectionGroup(GroupsList.Find('DGROUP')),RELOC_SEGREL);
              CurrObjSec.ObjRelocations.Add(objreloc);
            end;
        CurrObjSec.write(data,len);
      end;

{****************************************************************************
                                TOmfObjOutput
****************************************************************************}

    procedure TOmfObjOutput.AddSegment(const name, segclass, ovlname: string;
        Alignment: TOmfSegmentAlignment; Combination: TOmfSegmentCombination;
        Use: TOmfSegmentUse; Size: TObjSectionOfs);
      var
        s: TOmfRecord_SEGDEF;
      begin
        s:=TOmfRecord_SEGDEF.Create;
        Segments.Add(name,s);
        s.SegmentNameIndex:=LNames.Add(name);
        s.ClassNameIndex:=LNames.Add(segclass);
        s.OverlayNameIndex:=LNames.Add(ovlname);
        s.Alignment:=Alignment;
        s.Combination:=Combination;
        s.Use:=Use;
        s.SegmentLength:=Size;
      end;

    procedure TOmfObjOutput.AddGroup(const groupname: string; seglist: array of const);
      var
        g: TOmfRecord_GRPDEF;
        I: Integer;
        SegListStr: TSegmentList;
      begin
        g:=TOmfRecord_GRPDEF.Create;
        Groups.Add(groupname,g);
        g.GroupNameIndex:=LNames.Add(groupname);
        SetLength(SegListStr,Length(seglist));
        for I:=0 to High(seglist) do
          begin
            case seglist[I].VType of
              vtString:
                SegListStr[I]:=Segments.FindIndexOf(seglist[I].VString^);
              vtAnsiString:
                SegListStr[I]:=Segments.FindIndexOf(AnsiString(seglist[I].VAnsiString));
              vtWideString:
                SegListStr[I]:=Segments.FindIndexOf(AnsiString(WideString(seglist[I].VWideString)));
              vtUnicodeString:
                SegListStr[I]:=Segments.FindIndexOf(AnsiString(UnicodeString(seglist[I].VUnicodeString)));
              else
                internalerror(2015040402);
            end;
          end;
        g.SegmentList:=SegListStr;
      end;

    procedure TOmfObjOutput.AddGroup(const groupname: string; seglist: TSegmentList);
      var
        g: TOmfRecord_GRPDEF;
      begin
        g:=TOmfRecord_GRPDEF.Create;
        Groups.Add(groupname,g);
        g.GroupNameIndex:=LNames.Add(groupname);
        g.SegmentList:=Copy(seglist);
      end;

    procedure TOmfObjOutput.WriteSections(Data: TObjData);
      var
        i:longint;
        sec:TObjSection;
      begin
        for i:=0 to Data.ObjSectionList.Count-1 do
          begin
            sec:=TObjSection(Data.ObjSectionList[i]);
            WriteSectionContentAndFixups(sec);
            WriteLinNumRecords(TOmfObjSection(sec));
          end;
      end;

    procedure TOmfObjOutput.WriteSectionContentAndFixups(sec: TObjSection);
      const
        MaxChunkSize=$3fa;
      var
        RawRecord: TOmfRawRecord;
        ChunkStart,ChunkLen: DWord;
        ChunkFixupStart,ChunkFixupEnd: Integer;
        SegIndex: Integer;
        NextOfs: Integer;
        Is32BitLEDATA: Boolean;
        I: Integer;
      begin
        if (oso_data in sec.SecOptions) then
          begin
            if sec.Data=nil then
              internalerror(200403073);
            for I:=0 to sec.ObjRelocations.Count-1 do
              TOmfRelocation(sec.ObjRelocations[I]).BuildOmfFixup;
            SegIndex:=Segments.FindIndexOf(sec.Name);
            RawRecord:=TOmfRawRecord.Create;
            sec.data.seek(0);
            ChunkFixupStart:=0;
            ChunkFixupEnd:=-1;
            ChunkStart:=0;
            ChunkLen:=Min(MaxChunkSize, sec.Data.size-ChunkStart);
            while ChunkLen>0 do
            begin
              { find last fixup in the chunk }
              while (ChunkFixupEnd<(sec.ObjRelocations.Count-1)) and
                    (TOmfRelocation(sec.ObjRelocations[ChunkFixupEnd+1]).DataOffset<(ChunkStart+ChunkLen)) do
                inc(ChunkFixupEnd);
              { check if last chunk is crossing the chunk boundary, and trim ChunkLen if necessary }
              if (ChunkFixupEnd>=ChunkFixupStart) and
                ((TOmfRelocation(sec.ObjRelocations[ChunkFixupEnd]).DataOffset+
                  TOmfRelocation(sec.ObjRelocations[ChunkFixupEnd]).OmfFixup.LocationSize)>(ChunkStart+ChunkLen)) then
                begin
                  ChunkLen:=TOmfRelocation(sec.ObjRelocations[ChunkFixupEnd]).DataOffset-ChunkStart;
                  Dec(ChunkFixupEnd);
                end;
              { write LEDATA record }
              Is32BitLEDATA:=TOmfObjSection(sec).Use=suUse32;
              if Is32BitLEDATA then
                RawRecord.RecordType:=RT_LEDATA32
              else
                RawRecord.RecordType:=RT_LEDATA;
              NextOfs:=RawRecord.WriteIndexedRef(0,SegIndex);
              if Is32BitLEDATA then
                begin
                  RawRecord.RawData[NextOfs]:=Byte(ChunkStart);
                  RawRecord.RawData[NextOfs+1]:=Byte(ChunkStart shr 8);
                  RawRecord.RawData[NextOfs+2]:=Byte(ChunkStart shr 16);
                  RawRecord.RawData[NextOfs+3]:=Byte(ChunkStart shr 24);
                  Inc(NextOfs,4);
                end
              else
                begin
                  if ChunkStart>$ffff then
                    internalerror(2018052201);
                  RawRecord.RawData[NextOfs]:=Byte(ChunkStart);
                  RawRecord.RawData[NextOfs+1]:=Byte(ChunkStart shr 8);
                  Inc(NextOfs,2);
                end;
              sec.data.read(RawRecord.RawData[NextOfs], ChunkLen);
              Inc(NextOfs, ChunkLen);
              RawRecord.RecordLength:=NextOfs+1;
              RawRecord.CalculateChecksumByte;
              RawRecord.WriteTo(FWriter);
              { write FIXUPP record }
              if ChunkFixupEnd>=ChunkFixupStart then
                begin
                  RawRecord.RecordType:=RT_FIXUPP;
                  NextOfs:=0;
                  for I:=ChunkFixupStart to ChunkFixupEnd do
                    begin
                      TOmfRelocation(sec.ObjRelocations[I]).OmfFixup.DataRecordStartOffset:=ChunkStart;
                      NextOfs:=TOmfRelocation(sec.ObjRelocations[I]).OmfFixup.WriteAt(RawRecord,NextOfs);
                    end;
                  RawRecord.RecordLength:=NextOfs+1;
                  RawRecord.CalculateChecksumByte;
                  RawRecord.WriteTo(FWriter);
                end;
              { prepare next chunk }
              Inc(ChunkStart, ChunkLen);
              ChunkLen:=Min(MaxChunkSize, sec.Data.size-ChunkStart);
              ChunkFixupStart:=ChunkFixupEnd+1;
            end;
            RawRecord.Free;
          end;
      end;

    procedure TOmfObjOutput.WriteLinNumRecords(sec: TOmfObjSection);
      var
        SegIndex: Integer;
        RawRecord: TOmfRawRecord;
        LinNumRec: TOmfRecord_LINNUM_MsLink;
      begin
        if (oso_data in sec.SecOptions) then
          begin
            if sec.Data=nil then
              internalerror(200403073);
            if sec.LinNumEntries.Count=0 then
              exit;
            SegIndex:=Segments.FindIndexOf(sec.Name);
            RawRecord:=TOmfRawRecord.Create;
            LinNumRec:=TOmfRecord_LINNUM_MsLink.Create;
            LinNumRec.BaseGroup:=0;
            LinNumRec.BaseSegment:=SegIndex;
            LinNumRec.LineNumberList:=sec.LinNumEntries;

            while LinNumRec.NextIndex<sec.LinNumEntries.Count do
              begin
                LinNumRec.EncodeTo(RawRecord);
                RawRecord.WriteTo(FWriter);
              end;

            LinNumRec.Free;
            RawRecord.Free;
          end;
      end;

    procedure TOmfObjOutput.section_count_sections(p: TObject; arg: pointer);
      begin
        TOmfObjSection(p).index:=pinteger(arg)^;
        inc(pinteger(arg)^);
      end;

    procedure TOmfObjOutput.WritePUBDEFs(Data: TObjData);
      var
        PubNamesForSection: array of TFPHashObjectList;
        i: Integer;
        objsym: TObjSymbol;
        PublicNameElem: TOmfPublicNameElement;
        RawRecord: TOmfRawRecord;
        PubDefRec: TOmfRecord_PUBDEF;
        PrimaryGroupName: string;
      begin
        RawRecord:=TOmfRawRecord.Create;
        SetLength(PubNamesForSection,Data.ObjSectionList.Count);
        for i:=0 to Data.ObjSectionList.Count-1 do
          PubNamesForSection[i]:=TFPHashObjectList.Create;

        for i:=0 to Data.ObjSymbolList.Count-1 do
          begin
            objsym:=TObjSymbol(Data.ObjSymbolList[i]);
            if objsym.bind=AB_GLOBAL then
              begin
                PublicNameElem:=TOmfPublicNameElement.Create(PubNamesForSection[objsym.objsection.index-1],objsym.Name);
                PublicNameElem.PublicOffset:=objsym.offset;
                PublicNameElem.IsLocal:=False;
              end
            else if objsym.bind=AB_LOCAL then
              begin
                PublicNameElem:=TOmfPublicNameElement.Create(PubNamesForSection[objsym.objsection.index-1],objsym.Name);
                PublicNameElem.PublicOffset:=objsym.offset;
                PublicNameElem.IsLocal:=True;
              end
          end;

        for i:=0 to Data.ObjSectionList.Count-1 do
          if PubNamesForSection[i].Count>0 then
            begin
              PubDefRec:=TOmfRecord_PUBDEF.Create;
              PubDefRec.BaseSegmentIndex:=i+1;
              PrimaryGroupName:=TOmfObjSection(Data.ObjSectionList[i]).PrimaryGroup;
              if PrimaryGroupName<>'' then
                PubDefRec.BaseGroupIndex:=Groups.FindIndexOf(PrimaryGroupName)
              else
                PubDefRec.BaseGroupIndex:=0;
              PubDefRec.PublicNames:=PubNamesForSection[i];
              while PubDefRec.NextIndex<PubDefRec.PublicNames.Count do
                begin
                  PubDefRec.EncodeTo(RawRecord);
                  RawRecord.WriteTo(FWriter);
                end;
              PubDefRec.Free;
            end;

        for i:=0 to Data.ObjSectionList.Count-1 do
          FreeAndNil(PubNamesForSection[i]);
        RawRecord.Free;
      end;

    procedure TOmfObjOutput.WriteEXTDEFs(Data: TObjData);
      var
        ExtNames: TFPHashObjectList;
        RawRecord: TOmfRawRecord;
        i,idx: Integer;
        objsym: TObjSymbol;
        ExternalNameElem: TOmfExternalNameElement;
        ExtDefRec: TOmfRecord_EXTDEF;
      begin
        ExtNames:=TFPHashObjectList.Create;
        RawRecord:=TOmfRawRecord.Create;

        idx:=1;
        for i:=0 to Data.ObjSymbolList.Count-1 do
          begin
            objsym:=TObjSymbol(Data.ObjSymbolList[i]);
            if objsym.bind=AB_EXTERNAL then
              begin
                ExternalNameElem:=TOmfExternalNameElement.Create(ExtNames,objsym.Name);
                objsym.symidx:=idx;
                Inc(idx);
              end;
          end;

        if ExtNames.Count>0 then
          begin
            ExtDefRec:=TOmfRecord_EXTDEF.Create;
            ExtDefRec.ExternalNames:=ExtNames;
            while ExtDefRec.NextIndex<ExtDefRec.ExternalNames.Count do
              begin
                ExtDefRec.EncodeTo(RawRecord);
                RawRecord.WriteTo(FWriter);
              end;
            ExtDefRec.Free;
          end;

        ExtNames.Free;
        RawRecord.Free;
      end;

    function TOmfObjOutput.writeData(Data:TObjData):boolean;
      var
        RawRecord: TOmfRawRecord;
        Header: TOmfRecord_THEADR;
        Translator_COMENT: TOmfRecord_COMENT;
        DebugFormat_COMENT: TOmfRecord_COMENT;
        LinkPassSeparator_COMENT: TOmfRecord_COMENT;
        LNamesRec: TOmfRecord_LNAMES;
        ModEnd: TOmfRecord_MODEND;
        I: Integer;
        SegDef: TOmfRecord_SEGDEF;
        GrpDef: TOmfRecord_GRPDEF;
        DGroupSegments: TSegmentList;
        nsections: Integer;
        objsym: TObjSymbol;
      begin
        { calc amount of sections we have and set their index, starting with 1 }
        nsections:=1;
        data.ObjSectionList.ForEachCall(@section_count_sections,@nsections);
        { maximum amount of sections supported in the omf format is $7fff }
        if (nsections-1)>$7fff then
          internalerror(2015040701);

        { write header record }
        RawRecord:=TOmfRawRecord.Create;
        Header:=TOmfRecord_THEADR.Create;
        if cs_debuginfo in current_settings.moduleswitches then
          Header.ModuleName:=TOmfObjData(Data).MainSource
        else
          Header.ModuleName:=Data.Name;
        Header.EncodeTo(RawRecord);
        RawRecord.WriteTo(FWriter);
        Header.Free;

        { write translator COMENT header }
        Translator_COMENT:=TOmfRecord_COMENT.Create;
        Translator_COMENT.CommentClass:=CC_Translator;
        Translator_COMENT.CommentString:='FPC '+full_version_string+
        ' ['+date_string+'] for '+target_cpu_string+' - '+target_info.shortname;
        Translator_COMENT.EncodeTo(RawRecord);
        RawRecord.WriteTo(FWriter);
        Translator_COMENT.Free;

        if (target_dbg.id=dbg_codeview) or
           ((ds_dwarf_omf_linnum in current_settings.debugswitches) and
            (target_dbg.id in [dbg_dwarf2,dbg_dwarf3,dbg_dwarf4])) then
          begin
            DebugFormat_COMENT:=TOmfRecord_COMENT.Create;
            DebugFormat_COMENT.CommentClass:=CC_NewOmfExtension;
            DebugFormat_COMENT.CommentString:='';
            DebugFormat_COMENT.EncodeTo(RawRecord);
            RawRecord.WriteTo(FWriter);
            DebugFormat_COMENT.Free;
          end;

        LNames.Clear;
        LNames.Add('');  { insert an empty string, which has index 1 }
        FSegments.Clear;
        FSegments.Add('',nil);
        FGroups.Clear;
        FGroups.Add('',nil);

        for i:=0 to Data.ObjSectionList.Count-1 do
          with TOmfObjSection(Data.ObjSectionList[I]) do
            AddSegment(Name,ClassName,OverlayName,OmfAlignment,Combination,Use,Size);


        { create group "DGROUP" }
        SetLength(DGroupSegments,0);
        for i:=0 to Data.ObjSectionList.Count-1 do
          with TOmfObjSection(Data.ObjSectionList[I]) do
            if PrimaryGroup='DGROUP' then
              begin
                SetLength(DGroupSegments,Length(DGroupSegments)+1);
                DGroupSegments[High(DGroupSegments)]:=index;
              end;
        AddGroup('DGROUP',DGroupSegments);

        { write LNAMES record(s) }
        LNamesRec:=TOmfRecord_LNAMES.Create;
        LNamesRec.Names:=LNames;
        while LNamesRec.NextIndex<=LNames.Count do
          begin
            LNamesRec.EncodeTo(RawRecord);
            RawRecord.WriteTo(FWriter);
          end;
        LNamesRec.Free;

        { write SEGDEF record(s) }
        for I:=1 to Segments.Count-1 do
          begin
            SegDef:=TOmfRecord_SEGDEF(Segments[I]);
            SegDef.EncodeTo(RawRecord);
            RawRecord.WriteTo(FWriter);
          end;

        { write GRPDEF record(s) }
        for I:=1 to Groups.Count-1 do
          begin
            GrpDef:=TOmfRecord_GRPDEF(Groups[I]);
            GrpDef.EncodeTo(RawRecord);
            RawRecord.WriteTo(FWriter);
          end;

        { write PUBDEF record(s) }
        WritePUBDEFs(Data);

        { write EXTDEF record(s) }
        WriteEXTDEFs(Data);

        { write link pass separator }
        LinkPassSeparator_COMENT:=TOmfRecord_COMENT.Create;
        LinkPassSeparator_COMENT.CommentClass:=CC_LinkPassSeparator;
        LinkPassSeparator_COMENT.CommentString:=#1;
        LinkPassSeparator_COMENT.NoList:=True;
        LinkPassSeparator_COMENT.EncodeTo(RawRecord);
        RawRecord.WriteTo(FWriter);
        LinkPassSeparator_COMENT.Free;

        { write section content, interleaved with fixups }
        WriteSections(Data);

        { write MODEND record }
        ModEnd:=TOmfRecord_MODEND.Create;
        ModEnd.EncodeTo(RawRecord);
        RawRecord.WriteTo(FWriter);
        ModEnd.Free;

        RawRecord.Free;
        result:=true;
      end;

    constructor TOmfObjOutput.create(AWriter:TObjectWriter);
      begin
        inherited create(AWriter);
        cobjdata:=TOmfObjData;
        FLNames:=TOmfOrderedNameCollection.Create(False);
        FSegments:=TFPHashObjectList.Create;
        FSegments.Add('',nil);
        FGroups:=TFPHashObjectList.Create;
        FGroups.Add('',nil);
      end;

    destructor TOmfObjOutput.Destroy;
      begin
        FGroups.Free;
        FSegments.Free;
        FLNames.Free;
        inherited Destroy;
      end;

    procedure TOmfObjOutput.WriteDllImport(const dllname,afuncname,mangledname: string; ordnr: longint; isvar: boolean);
      var
        RawRecord: TOmfRawRecord;
        Header: TOmfRecord_THEADR;
        DllImport_COMENT: TOmfRecord_COMENT;
        ModEnd: TOmfRecord_MODEND;
      begin
        { write header record }
        RawRecord:=TOmfRawRecord.Create;
        Header:=TOmfRecord_THEADR.Create;
        Header.ModuleName:=mangledname;
        Header.EncodeTo(RawRecord);
        RawRecord.WriteTo(FWriter);
        Header.Free;

        { write IMPDEF record }
        DllImport_COMENT:=TOmfRecord_COMENT.Create;
        DllImport_COMENT.CommentClass:=CC_OmfExtension;
        if ordnr <= 0 then
          begin
            if afuncname=mangledname then
              DllImport_COMENT.CommentString:=#1#0+Chr(Length(mangledname))+mangledname+Chr(Length(dllname))+dllname+#0
            else
              DllImport_COMENT.CommentString:=#1#0+Chr(Length(mangledname))+mangledname+Chr(Length(dllname))+dllname+Chr(Length(afuncname))+afuncname;
          end
        else
          DllImport_COMENT.CommentString:=#1#1+Chr(Length(mangledname))+mangledname+Chr(Length(dllname))+dllname+Chr(ordnr and $ff)+Chr((ordnr shr 8) and $ff);
        DllImport_COMENT.EncodeTo(RawRecord);
        RawRecord.WriteTo(FWriter);
        DllImport_COMENT.Free;

        { write MODEND record }
        ModEnd:=TOmfRecord_MODEND.Create;
        ModEnd.EncodeTo(RawRecord);
        RawRecord.WriteTo(FWriter);
        ModEnd.Free;

        RawRecord.Free;
      end;

{****************************************************************************
                               TOmfObjInput
****************************************************************************}

    function TOmfObjInput.PeekNextRecordType: Byte;
      var
        OldPos: LongInt;
      begin
        OldPos:=FReader.Pos;
        if not FReader.read(Result, 1) then
          begin
            InputError('Unexpected end of file');
            Result:=0;
            exit;
          end;
        FReader.seek(OldPos);
      end;

    function TOmfObjInput.ReadLNames(RawRec: TOmfRawRecord): Boolean;
      var
        LNamesRec: TOmfRecord_LNAMES;
      begin
        Result:=False;
        LNamesRec:=TOmfRecord_LNAMES.Create;
        LNamesRec.Names:=LNames;
        LNamesRec.DecodeFrom(RawRec);
        LNamesRec.Free;
        Result:=True;
      end;

    function TOmfObjInput.ReadSegDef(RawRec: TOmfRawRecord; objdata: TObjData): Boolean;
      var
        SegDefRec: TOmfRecord_SEGDEF;
        SegmentName,SegClassName,OverlayName: string;
        SecAlign: LongInt;
        secoptions: TObjSectionOptions;
        objsec: TOmfObjSection;
      begin
        Result:=False;
        SegDefRec:=TOmfRecord_SEGDEF.Create;
        SegDefRec.DecodeFrom(RawRec);
        if (SegDefRec.SegmentNameIndex<1) or (SegDefRec.SegmentNameIndex>LNames.Count) then
          begin
            InputError('Segment name index out of range');
            SegDefRec.Free;
            exit;
          end;
        SegmentName:=LNames[SegDefRec.SegmentNameIndex];
        if (SegDefRec.ClassNameIndex<1) or (SegDefRec.ClassNameIndex>LNames.Count) then
          begin
            InputError('Segment class name index out of range');
            SegDefRec.Free;
            exit;
          end;
        SegClassName:=LNames[SegDefRec.ClassNameIndex];
        if (SegDefRec.OverlayNameIndex<1) or (SegDefRec.OverlayNameIndex>LNames.Count) then
          begin
            InputError('Segment overlay name index out of range');
            SegDefRec.Free;
            exit;
          end;
        OverlayName:=LNames[SegDefRec.OverlayNameIndex];
        SecAlign:=1; // otherwise warning prohibits compilation
        case SegDefRec.Alignment of
          saRelocatableByteAligned:
            SecAlign:=1;
          saRelocatableWordAligned:
            SecAlign:=2;
          saRelocatableParaAligned:
            SecAlign:=16;
          saRelocatableDWordAligned:
            SecAlign:=4;
          saRelocatablePageAligned:
            SecAlign:=256;
          saNotSupported:
            SecAlign:=4096;
          saAbsolute:
            begin
              InputError('Absolute segment alignment not supported');
              SegDefRec.Free;
              exit;
            end;
          saNotDefined:
            begin
              InputError('Invalid (unsupported/undefined) OMF segment alignment');
              SegDefRec.Free;
              exit;
            end;
        end;
        if not CaseSensitiveSegments then
          begin
            SegmentName:=UpCase(SegmentName);
            SegClassName:=UpCase(SegClassName);
            OverlayName:=UpCase(OverlayName);
          end;
        { hack for supporting object modules, generated by Borland's BINOBJ tool }
        if (SegClassName='') and (SegmentName='CODE') then
          begin
            SegmentName:=InputFileName;
            SegClassName:='CODE';
          end;
        secoptions:=[];
        objsec:=TOmfObjSection(objdata.createsection(SegmentName+'||'+SegClassName,SecAlign,secoptions,false));
        objsec.FClassName:=SegClassName;
        objsec.FOverlayName:=OverlayName;
        objsec.FCombination:=SegDefRec.Combination;
        objsec.FUse:=SegDefRec.Use;
        if SegDefRec.SegmentLength>High(objsec.Size) then
          begin
            InputError('Segment too large');
            SegDefRec.Free;
            exit;
          end;
        objsec.Size:=SegDefRec.SegmentLength;
        if (SegClassName='HEAP') or
           (SegClassName='STACK') or (SegDefRec.Combination=scStack) or
           (SegClassName='BEGDATA') or
           (SegmentName='FPC') then
          objsec.SecOptions:=objsec.SecOptions+[oso_keep];
        SegDefRec.Free;
        Result:=True;
      end;

    function TOmfObjInput.ReadGrpDef(RawRec: TOmfRawRecord; objdata: TObjData): Boolean;
      var
        GrpDefRec: TOmfRecord_GRPDEF;
        GroupName: string;
        SecGroup: TObjSectionGroup;
        i,SegIndex: Integer;
      begin
        Result:=False;
        GrpDefRec:=TOmfRecord_GRPDEF.Create;
        GrpDefRec.DecodeFrom(RawRec);
        if (GrpDefRec.GroupNameIndex<1) or (GrpDefRec.GroupNameIndex>LNames.Count) then
          begin
            InputError('Group name index out of range');
            GrpDefRec.Free;
            exit;
          end;
        GroupName:=LNames[GrpDefRec.GroupNameIndex];
        if not CaseSensitiveSegments then
          GroupName:=UpCase(GroupName);
        SecGroup:=objdata.createsectiongroup(GroupName);
        SetLength(SecGroup.members,Length(GrpDefRec.SegmentList));
        for i:=0 to Length(GrpDefRec.SegmentList)-1 do
          begin
            SegIndex:=GrpDefRec.SegmentList[i];
            if (SegIndex<1) or (SegIndex>objdata.ObjSectionList.Count) then
              begin
                InputError('Segment name index out of range in group definition');
                GrpDefRec.Free;
                exit;
              end;
            SecGroup.members[i]:=TOmfObjSection(objdata.ObjSectionList[SegIndex-1]);
          end;
        GrpDefRec.Free;
        Result:=True;
      end;

    function TOmfObjInput.ReadExtDef(RawRec: TOmfRawRecord; objdata: TObjData): Boolean;
      var
        ExtDefRec: TOmfRecord_EXTDEF;
        ExtDefElem: TOmfExternalNameElement;
        OldCount,NewCount,i: Integer;
        objsym: TObjSymbol;
        symname: TSymStr;
      begin
        Result:=False;
        ExtDefRec:=TOmfRecord_EXTDEF.Create;
        ExtDefRec.ExternalNames:=ExtDefs;
        OldCount:=ExtDefs.Count;
        ExtDefRec.DecodeFrom(RawRec);
        NewCount:=ExtDefs.Count;
        for i:=OldCount to NewCount-1 do
          begin
            ExtDefElem:=TOmfExternalNameElement(ExtDefs[i]);
            symname:=ExtDefElem.Name;
            if not CaseSensitiveSymbols then
              symname:=UpCase(symname);
            objsym:=objdata.CreateSymbol(symname);
            objsym.bind:=AB_EXTERNAL;
            objsym.typ:=AT_FUNCTION;
            objsym.objsection:=nil;
            objsym.offset:=0;
            objsym.size:=0;
          end;
        ExtDefRec.Free;
        Result:=True;
      end;

    function TOmfObjInput.ReadPubDef(RawRec: TOmfRawRecord; objdata:TObjData): Boolean;
      var
        PubDefRec: TOmfRecord_PUBDEF;
        PubDefElem: TOmfPublicNameElement;
        OldCount,NewCount,i: Integer;
        basegroup: TObjSectionGroup;
        objsym: TObjSymbol;
        objsec: TOmfObjSection;
        symname: TSymStr;
      begin
        Result:=False;
        PubDefRec:=TOmfRecord_PUBDEF.Create;
        PubDefRec.PublicNames:=PubDefs;
        OldCount:=PubDefs.Count;
        PubDefRec.DecodeFrom(RawRec);
        NewCount:=PubDefs.Count;
        if (PubDefRec.BaseGroupIndex<0) or (PubDefRec.BaseGroupIndex>objdata.GroupsList.Count) then
          begin
            InputError('Public symbol''s group name index out of range');
            PubDefRec.Free;
            exit;
          end;
        if PubDefRec.BaseGroupIndex<>0 then
          basegroup:=TObjSectionGroup(objdata.GroupsList[PubDefRec.BaseGroupIndex-1])
        else
          basegroup:=nil;
        if (PubDefRec.BaseSegmentIndex<0) or (PubDefRec.BaseSegmentIndex>objdata.ObjSectionList.Count) then
          begin
            InputError('Public symbol''s segment name index out of range');
            PubDefRec.Free;
            exit;
          end;
        if PubDefRec.BaseSegmentIndex=0 then
          begin
            InputError('Public symbol uses absolute addressing, which is not supported by this linker');
            PubDefRec.Free;
            exit;
          end;
        objsec:=TOmfObjSection(objdata.ObjSectionList[PubDefRec.BaseSegmentIndex-1]);
        for i:=OldCount to NewCount-1 do
          begin
            PubDefElem:=TOmfPublicNameElement(PubDefs[i]);
            symname:=PubDefElem.Name;
            if not CaseSensitiveSymbols then
              symname:=UpCase(symname);
            objsym:=objdata.CreateSymbol(symname);
            if PubDefElem.IsLocal then
              objsym.bind:=AB_LOCAL
            else
              objsym.bind:=AB_GLOBAL;
            objsym.typ:=AT_FUNCTION;
            objsym.group:=basegroup;
            objsym.objsection:=objsec;
            objsym.offset:=PubDefElem.PublicOffset;
            objsym.size:=0;
          end;
        PubDefRec.Free;
        Result:=True;
      end;

    function TOmfObjInput.ReadModEnd(RawRec: TOmfRawRecord; objdata:TObjData): Boolean;
      var
        ModEndRec: TOmfRecord_MODEND;
        objsym: TObjSymbol;
        objsec: TOmfObjSection;
        basegroup: TObjSectionGroup;
      begin
        Result:=False;
        ModEndRec:=TOmfRecord_MODEND.Create;
        ModEndRec.DecodeFrom(RawRec);
        if ModEndRec.HasStartAddress then
          begin
            if not ModEndRec.LogicalStartAddress then
              begin
                InputError('Physical start address not supported');
                ModEndRec.Free;
                exit;
              end;
            if not (ModEndRec.TargetMethod in [ftmSegmentIndex,ftmSegmentIndexNoDisp]) then
              begin
                InputError('Target method for start address other than "Segment Index" is not supported');
                ModEndRec.Free;
                exit;
              end;
            if (ModEndRec.TargetDatum<1) or (ModEndRec.TargetDatum>objdata.ObjSectionList.Count) then
              begin
                InputError('Segment name index for start address out of range');
                ModEndRec.Free;
                exit;
              end;
            case ModEndRec.FrameMethod of
              ffmSegmentIndex:
                begin
                  if (ModEndRec.FrameDatum<1) or (ModEndRec.FrameDatum>objdata.ObjSectionList.Count) then
                    begin
                      InputError('Frame segment name index for start address out of range');
                      ModEndRec.Free;
                      exit;
                    end;
                  if ModEndRec.FrameDatum<>ModEndRec.TargetDatum then
                    begin
                      InputError('Frame segment different than target segment is not supported supported for start address');
                      ModEndRec.Free;
                      exit;
                    end;
                  basegroup:=nil;
                end;
              ffmGroupIndex:
                begin
                  if (ModEndRec.FrameDatum<1) or (ModEndRec.FrameDatum>objdata.GroupsList.Count) then
                    begin
                      InputError('Frame group name index for start address out of range');
                      ModEndRec.Free;
                      exit;
                    end;
                  basegroup:=TObjSectionGroup(objdata.GroupsList[ModEndRec.FrameDatum-1]);
                end;
              else
                begin
                  InputError('Frame method for start address other than "Segment Index" or "Group Index" is not supported');
                  ModEndRec.Free;
                  exit;
                end;
            end;
            objsec:=TOmfObjSection(objdata.ObjSectionList[ModEndRec.TargetDatum-1]);

            objsym:=objdata.CreateSymbol('..start');
            objsym.bind:=AB_GLOBAL;
            objsym.typ:=AT_FUNCTION;
            objsym.group:=basegroup;
            objsym.objsection:=objsec;
            objsym.offset:=ModEndRec.TargetDisplacement;
            objsym.size:=0;
          end;
        ModEndRec.Free;
        Result:=True;
      end;

    function TOmfObjInput.ReadLeOrLiDataAndFixups(RawRec: TOmfRawRecord; objdata: TObjData): Boolean;
      var
        Is32Bit: Boolean;
        NextOfs: Integer;
        SegmentIndex: Integer;
        EnumeratedDataOffset: DWord;
        BlockLength: Integer;
        objsec: TOmfObjSection;
        FixupRawRec: TOmfRawRecord=nil;
        Fixup: TOmfSubRecord_FIXUP;
        Thread: TOmfSubRecord_THREAD;
        FixuppWithoutLeOrLiData: Boolean=False;
      begin
        Result:=False;
        case RawRec.RecordType of
          RT_LEDATA,RT_LEDATA32:
            begin
              Is32Bit:=RawRec.RecordType=RT_LEDATA32;
              NextOfs:=RawRec.ReadIndexedRef(0,SegmentIndex);
              if Is32Bit then
                begin
                  if (NextOfs+3)>=RawRec.RecordLength then
                    internalerror(2015040504);
                  EnumeratedDataOffset := RawRec.RawData[NextOfs]+
                                         (RawRec.RawData[NextOfs+1] shl 8)+
                                         (RawRec.RawData[NextOfs+2] shl 16)+
                                         (RawRec.RawData[NextOfs+3] shl 24);
                  Inc(NextOfs,4);
                end
              else
                begin
                  if (NextOfs+1)>=RawRec.RecordLength then
                    internalerror(2015040504);
                  EnumeratedDataOffset := RawRec.RawData[NextOfs]+
                                         (RawRec.RawData[NextOfs+1] shl 8);
                  Inc(NextOfs,2);
                end;
              BlockLength:=RawRec.RecordLength-NextOfs-1;
              if BlockLength<0 then
                internalerror(2015060501);
              if BlockLength>1024 then
                begin
                  InputError('LEDATA contains more than 1024 bytes of data');
                  exit;
                end;

              if (SegmentIndex<1) or (SegmentIndex>objdata.ObjSectionList.Count) then
                begin
                  InputError('Segment index in LEDATA field is out of range');
                  exit;
                end;
              objsec:=TOmfObjSection(objdata.ObjSectionList[SegmentIndex-1]);

              objsec.SecOptions:=objsec.SecOptions+[oso_Data];
              if (objsec.Data.Size>EnumeratedDataOffset) then
                begin
                  InputError('LEDATA enumerated data offset field out of sequence');
                  exit;
                end;
              if (EnumeratedDataOffset+BlockLength)>objsec.Size then
                begin
                  InputError('LEDATA goes beyond the segment size declared in the SEGDEF record');
                  exit;
                end;
              objsec.Data.seek(EnumeratedDataOffset);
              objsec.Data.write(RawRec.RawData[NextOfs],BlockLength);
            end;
          RT_LIDATA,RT_LIDATA32:
            begin
              InputError('LIDATA records are not supported');
              exit;
            end;
          RT_FIXUPP,RT_FIXUPP32:
            begin
              FixuppWithoutLeOrLiData:=True;
              { a hack, used to indicate, that we must process this record       }
              { (RawRec) first in the FIXUPP record processing loop that follows }
              FixupRawRec:=RawRec;
            end;
          else
            internalerror(2015040301);
        end;

        { also read all the FIXUPP records that may follow;                     }
        { (FixupRawRec=RawRec) indicates that we must process RawRec first, but }
        { without freeing it                                                    }
        while (FixupRawRec=RawRec) or (PeekNextRecordType in [RT_FIXUPP,RT_FIXUPP32]) do
          begin
            if FixupRawRec<>RawRec then
              begin
                FixupRawRec:=TOmfRawRecord.Create;
                FixupRawRec.ReadFrom(FReader);
                if not FRawRecord.VerifyChecksumByte then
                  begin
                    InputError('Invalid checksum in OMF record');
                    FixupRawRec.Free;
                    exit;
                  end;
              end;
            NextOfs:=0;
            Thread:=TOmfSubRecord_THREAD.Create;
            Fixup:=TOmfSubRecord_FIXUP.Create;
            Fixup.Is32Bit:=FixupRawRec.RecordType=RT_FIXUPP32;
            Fixup.DataRecordStartOffset:=EnumeratedDataOffset;
            while NextOfs<(FixupRawRec.RecordLength-1) do
              begin
                if (FixupRawRec.RawData[NextOfs] and $80)<>0 then
                  begin
                    { FIXUP subrecord }
                    if FixuppWithoutLeOrLiData then
                      begin
                        InputError('FIXUP subrecord without previous LEDATA or LIDATA record');
                        Fixup.Free;
                        Thread.Free;
                        if FixupRawRec<>RawRec then
                          FixupRawRec.Free;
                        exit;
                      end;
                    NextOfs:=Fixup.ReadAt(FixupRawRec,NextOfs);
                    Fixup.ResolveByThread(FFixupThreads);
                    ImportOmfFixup(objdata,objsec,Fixup);
                  end
                else
                  begin
                    { THREAD subrecord }
                    NextOfs:=Thread.ReadAt(FixupRawRec,NextOfs);
                    Thread.ApplyTo(FFixupThreads);
                  end;
              end;
            Fixup.Free;
            Thread.Free;
            if FixupRawRec<>RawRec then
              FixupRawRec.Free;
            { always set it to null, so that we read the next record on the next }
            { loop iteration (this ensures that FixupRawRec<>RawRec, without     }
            { freeing RawRec)                                                    }
            FixupRawRec:=nil;
          end;
        Result:=True;
      end;

    function TOmfObjInput.ImportOmfFixup(objdata: TObjData; objsec: TOmfObjSection; Fixup: TOmfSubRecord_FIXUP): Boolean;
      var
        reloc: TOmfRelocation;
        sym: TObjSymbol;
        RelocType: TObjRelocationType;
        target_section: TOmfObjSection;
        target_group: TObjSectionGroup;
      begin
        Result:=False;

        { range check location }
        if (Fixup.LocationOffset+Fixup.LocationSize)>objsec.Size then
          begin
            InputError('Fixup location exceeds the current segment boundary');
            exit;
          end;

        { range check target datum }
        case Fixup.TargetMethod of
          ftmSegmentIndex:
            if (Fixup.TargetDatum<1) or (Fixup.TargetDatum>objdata.ObjSectionList.Count) then
              begin
                InputError('Segment name index in SI(<segment name>),<displacement> fixup target is out of range');
                exit;
              end;
          ftmSegmentIndexNoDisp:
            if (Fixup.TargetDatum<1) or (Fixup.TargetDatum>objdata.ObjSectionList.Count) then
              begin
                InputError('Segment name index in SI(<segment name>) fixup target is out of range');
                exit;
              end;
          ftmGroupIndex:
            if (Fixup.TargetDatum<1) or (Fixup.TargetDatum>objdata.GroupsList.Count) then
              begin
                InputError('Group name index in GI(<group name>),<displacement> fixup target is out of range');
                exit;
              end;
          ftmGroupIndexNoDisp:
            if (Fixup.TargetDatum<1) or (Fixup.TargetDatum>objdata.GroupsList.Count) then
              begin
                InputError('Group name index in GI(<group name>) fixup target is out of range');
                exit;
              end;
          ftmExternalIndex:
            if (Fixup.TargetDatum<1) or (Fixup.TargetDatum>ExtDefs.Count) then
              begin
                InputError('External symbol name index in EI(<symbol name>),<displacement> fixup target is out of range');
                exit;
              end;
          ftmExternalIndexNoDisp:
            if (Fixup.TargetDatum<1) or (Fixup.TargetDatum>ExtDefs.Count) then
              begin
                InputError('External symbol name index in EI(<symbol name>) fixup target is out of range');
                exit;
              end;
        end;

        { range check frame datum }
        case Fixup.FrameMethod of
          ffmSegmentIndex:
            if (Fixup.FrameDatum<1) or (Fixup.FrameDatum>objdata.ObjSectionList.Count) then
              begin
                InputError('Segment name index in SI(<segment name>) fixup frame is out of range');
                exit;
              end;
          ffmGroupIndex:
            if (Fixup.FrameDatum<1) or (Fixup.FrameDatum>objdata.GroupsList.Count) then
              begin
                InputError('Group name index in GI(<group name>) fixup frame is out of range');
                exit;
              end;
          ffmExternalIndex:
            if (Fixup.TargetDatum<1) or (Fixup.TargetDatum>ExtDefs.Count) then
              begin
                InputError('External symbol name index in EI(<symbol name>) fixup frame is out of range');
                exit;
              end;
        end;

        if Fixup.TargetMethod in [ftmExternalIndex,ftmExternalIndexNoDisp] then
          begin
            sym:=objdata.symbolref(TOmfExternalNameElement(ExtDefs[Fixup.TargetDatum-1]).Name);
            RelocType:=RELOC_NONE;
            case Fixup.LocationType of
              fltOffset:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_ABSOLUTE16;
                  fmSelfRelative:
                    RelocType:=RELOC_RELATIVE16;
                end;
              fltOffset32:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_ABSOLUTE32;
                  fmSelfRelative:
                    RelocType:=RELOC_RELATIVE32;
                end;
              fltBase:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_SEG;
                  fmSelfRelative:
                    RelocType:=RELOC_SEGREL;
                end;
              fltFarPointer:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_FARPTR;
                  fmSelfRelative:
                    RelocType:=RELOC_FARPTR_RELATIVEOFFSET;
                end;
              fltFarPointer48:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_FARPTR48;
                  fmSelfRelative:
                    RelocType:=RELOC_FARPTR48_RELATIVEOFFSET;
                end;
            end;
            if RelocType=RELOC_NONE then
              begin
                InputError('Unsupported fixup location type '+tostr(Ord(Fixup.LocationType))+' with mode '+tostr(ord(Fixup.Mode))+' in external reference to '+sym.Name);
                exit;
              end;
            reloc:=TOmfRelocation.CreateSymbol(Fixup.LocationOffset,sym,RelocType);
            objsec.ObjRelocations.Add(reloc);
            case Fixup.FrameMethod of
              ffmTarget:
                {nothing};
              ffmGroupIndex:
                reloc.FrameGroup:=TObjSectionGroup(objdata.GroupsList[Fixup.FrameDatum-1]).Name;
              else
                begin
                  InputError('Unsupported frame method '+IntToStr(Ord(Fixup.FrameMethod))+' in external reference to '+sym.Name);
                  exit;
                end;
            end;
            if Fixup.TargetDisplacement<>0 then
              begin
                InputError('Unsupported nonzero target displacement '+IntToStr(Fixup.TargetDisplacement)+' in external reference to '+sym.Name);
                exit;
              end;
          end
        else if Fixup.TargetMethod in [ftmSegmentIndex,ftmSegmentIndexNoDisp] then
          begin
            target_section:=TOmfObjSection(objdata.ObjSectionList[Fixup.TargetDatum-1]);
            RelocType:=RELOC_NONE;
            case Fixup.LocationType of
              fltOffset:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_ABSOLUTE16;
                  fmSelfRelative:
                    RelocType:=RELOC_RELATIVE16;
                end;
              fltOffset32:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_ABSOLUTE32;
                  fmSelfRelative:
                    RelocType:=RELOC_RELATIVE32;
                end;
              fltBase:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_SEG;
                  fmSelfRelative:
                    RelocType:=RELOC_SEGREL;
                end;
              fltFarPointer:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_FARPTR;
                  fmSelfRelative:
                    RelocType:=RELOC_FARPTR_RELATIVEOFFSET;
                end;
              fltFarPointer48:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_FARPTR48;
                  fmSelfRelative:
                    RelocType:=RELOC_FARPTR48_RELATIVEOFFSET;
                end;
            end;
            if RelocType=RELOC_NONE then
              begin
                InputError('Unsupported fixup location type '+tostr(Ord(Fixup.LocationType))+' with mode '+tostr(ord(Fixup.Mode)));
                exit;
              end;
            reloc:=TOmfRelocation.CreateSection(Fixup.LocationOffset,target_section,RelocType);
            objsec.ObjRelocations.Add(reloc);
            case Fixup.FrameMethod of
              ffmTarget:
                {nothing};
              ffmGroupIndex:
                reloc.FrameGroup:=TObjSectionGroup(objdata.GroupsList[Fixup.FrameDatum-1]).Name;
              else
                begin
                  InputError('Unsupported frame method '+IntToStr(Ord(Fixup.FrameMethod))+' in reference to segment '+target_section.Name);
                  exit;
                end;
            end;
            if Fixup.TargetDisplacement<>0 then
              begin
                InputError('Unsupported nonzero target displacement '+IntToStr(Fixup.TargetDisplacement)+' in reference to segment '+target_section.Name);
                exit;
              end;
          end
        else if Fixup.TargetMethod in [ftmGroupIndex,ftmGroupIndexNoDisp] then
          begin
            target_group:=TObjSectionGroup(objdata.GroupsList[Fixup.TargetDatum-1]);
            RelocType:=RELOC_NONE;
            case Fixup.LocationType of
              fltOffset:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_ABSOLUTE16;
                  fmSelfRelative:
                    RelocType:=RELOC_RELATIVE16;
                end;
              fltOffset32:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_ABSOLUTE32;
                  fmSelfRelative:
                    RelocType:=RELOC_RELATIVE32;
                end;
              fltBase:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_SEG;
                  fmSelfRelative:
                    RelocType:=RELOC_SEGREL;
                end;
              fltFarPointer:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_FARPTR;
                  fmSelfRelative:
                    RelocType:=RELOC_FARPTR_RELATIVEOFFSET;
                end;
              fltFarPointer48:
                case Fixup.Mode of
                  fmSegmentRelative:
                    RelocType:=RELOC_FARPTR48;
                  fmSelfRelative:
                    RelocType:=RELOC_FARPTR48_RELATIVEOFFSET;
                end;
            end;
            if RelocType=RELOC_NONE then
              begin
                InputError('Unsupported fixup location type '+tostr(Ord(Fixup.LocationType))+' with mode '+tostr(ord(Fixup.Mode)));
                exit;
              end;
            reloc:=TOmfRelocation.CreateGroup(Fixup.LocationOffset,target_group,RelocType);
            objsec.ObjRelocations.Add(reloc);
            case Fixup.FrameMethod of
              ffmTarget:
                {nothing};
              else
                begin
                  InputError('Unsupported frame method '+IntToStr(Ord(Fixup.FrameMethod))+' in reference to group '+target_group.Name);
                  exit;
                end;
            end;
            if Fixup.TargetDisplacement<>0 then
              begin
                InputError('Unsupported nonzero target displacement '+IntToStr(Fixup.TargetDisplacement)+' in reference to group '+target_group.Name);
                exit;
              end;
          end
        else
          begin
            {todo: convert other fixup types as well }
            InputError('Unsupported fixup target method '+IntToStr(Ord(Fixup.TargetMethod)));
            exit;
          end;

        Result:=True;
      end;

    constructor TOmfObjInput.create;
      begin
        inherited create;
        cobjdata:=TOmfObjData;
        FLNames:=TOmfOrderedNameCollection.Create(True);
        FExtDefs:=TFPHashObjectList.Create;
        FPubDefs:=TFPHashObjectList.Create;
        FFixupThreads:=TOmfThreads.Create;
        FRawRecord:=TOmfRawRecord.Create;
        CaseSensitiveSegments:=False;
        CaseSensitiveSymbols:=True;
      end;

    destructor TOmfObjInput.destroy;
      begin
        FRawRecord.Free;
        FFixupThreads.Free;
        FPubDefs.Free;
        FExtDefs.Free;
        FLNames.Free;
        inherited destroy;
      end;

    class function TOmfObjInput.CanReadObjData(AReader: TObjectreader): boolean;
      var
        b: Byte;
      begin
        result:=false;
        if AReader.Read(b,sizeof(b)) then
          begin
            if b=RT_THEADR then
            { TODO: check additional fields }
              result:=true;
          end;
        AReader.Seek(0);
      end;

    function TOmfObjInput.ReadObjData(AReader: TObjectreader; out objdata: TObjData): boolean;
      begin
        FReader:=AReader;
        InputFileName:=AReader.FileName;
        objdata:=CObjData.Create(InputFileName);
        result:=false;
        LNames.Clear;
        ExtDefs.Clear;
        FRawRecord.ReadFrom(FReader);
        if not FRawRecord.VerifyChecksumByte then
          begin
            InputError('Invalid checksum in OMF record');
            exit;
          end;
        if FRawRecord.RecordType<>RT_THEADR then
          begin
            InputError('Can''t read OMF header');
            exit;
          end;
        repeat
          FRawRecord.ReadFrom(FReader);
          if not FRawRecord.VerifyChecksumByte then
            begin
              InputError('Invalid checksum in OMF record');
              exit;
            end;
          case FRawRecord.RecordType of
            RT_LNAMES:
              if not ReadLNames(FRawRecord) then
                exit;
            RT_SEGDEF,RT_SEGDEF32:
              if not ReadSegDef(FRawRecord,objdata) then
                exit;
            RT_GRPDEF:
              if not ReadGrpDef(FRawRecord,objdata) then
                exit;
            RT_COMENT:
              begin
                {todo}
              end;
            RT_EXTDEF:
              if not ReadExtDef(FRawRecord,objdata) then
                exit;
            RT_LPUBDEF,RT_LPUBDEF32,
            RT_PUBDEF,RT_PUBDEF32:
              if not ReadPubDef(FRawRecord,objdata) then
                exit;
            RT_LEDATA,RT_LEDATA32,
            RT_LIDATA,RT_LIDATA32,
            RT_FIXUPP,RT_FIXUPP32:
              if not ReadLeOrLiDataAndFixups(FRawRecord,objdata) then
                exit;
            RT_MODEND,RT_MODEND32:
              if not ReadModEnd(FRawRecord,objdata) then
                exit;
            RT_LINNUM,RT_LINNUM32:
              ;
            else
              begin
                InputError('Unsupported OMF record type $'+HexStr(FRawRecord.RecordType,2));
                exit;
              end;
          end;
        until FRawRecord.RecordType in [RT_MODEND,RT_MODEND32];
        result:=true;
      end;

{****************************************************************************
                               TMZExeHeader
****************************************************************************}

    procedure TMZExeHeader.SetHeaderSizeAlignment(AValue: Integer);
      begin
        if (AValue<16) or ((AValue mod 16) <> 0) then
          Internalerror(2015060601);
        FHeaderSizeAlignment:=AValue;
      end;

    constructor TMZExeHeader.Create;
      begin
        FHeaderSizeAlignment:=16;
      end;

    procedure TMZExeHeader.WriteTo(aWriter: TObjectWriter);
      var
        NumRelocs: Word;
        HeaderSizeInBytes: DWord;
        HeaderParagraphs: Word;
        RelocTableOffset: Word;
        BytesInLastBlock: Word;
        BlocksInFile: Word;
        HeaderBytes: array [0..$1B] of Byte;
        RelocBytes: array [0..3] of Byte;
        TotalExeSize: DWord;
        i: Integer;
      begin
        NumRelocs:=Length(Relocations);
        RelocTableOffset:=$1C+Length(ExtraHeaderData);
        HeaderSizeInBytes:=Align(RelocTableOffset+4*NumRelocs,16);
        HeaderParagraphs:=HeaderSizeInBytes div 16;
        TotalExeSize:=HeaderSizeInBytes+LoadableImageSize;
        BlocksInFile:=(TotalExeSize+511) div 512;
        BytesInLastBlock:=TotalExeSize mod 512;

        HeaderBytes[$00]:=$4D;  { 'M' }
        HeaderBytes[$01]:=$5A;  { 'Z' }
        HeaderBytes[$02]:=Byte(BytesInLastBlock);
        HeaderBytes[$03]:=Byte(BytesInLastBlock shr 8);
        HeaderBytes[$04]:=Byte(BlocksInFile);
        HeaderBytes[$05]:=Byte(BlocksInFile shr 8);
        HeaderBytes[$06]:=Byte(NumRelocs);
        HeaderBytes[$07]:=Byte(NumRelocs shr 8);
        HeaderBytes[$08]:=Byte(HeaderParagraphs);
        HeaderBytes[$09]:=Byte(HeaderParagraphs shr 8);
        HeaderBytes[$0A]:=Byte(MinExtraParagraphs);
        HeaderBytes[$0B]:=Byte(MinExtraParagraphs shr 8);
        HeaderBytes[$0C]:=Byte(MaxExtraParagraphs);
        HeaderBytes[$0D]:=Byte(MaxExtraParagraphs shr 8);
        HeaderBytes[$0E]:=Byte(InitialSS);
        HeaderBytes[$0F]:=Byte(InitialSS shr 8);
        HeaderBytes[$10]:=Byte(InitialSP);
        HeaderBytes[$11]:=Byte(InitialSP shr 8);
        HeaderBytes[$12]:=Byte(Checksum);
        HeaderBytes[$13]:=Byte(Checksum shr 8);
        HeaderBytes[$14]:=Byte(InitialIP);
        HeaderBytes[$15]:=Byte(InitialIP shr 8);
        HeaderBytes[$16]:=Byte(InitialCS);
        HeaderBytes[$17]:=Byte(InitialCS shr 8);
        HeaderBytes[$18]:=Byte(RelocTableOffset);
        HeaderBytes[$19]:=Byte(RelocTableOffset shr 8);
        HeaderBytes[$1A]:=Byte(OverlayNumber);
        HeaderBytes[$1B]:=Byte(OverlayNumber shr 8);
        aWriter.write(HeaderBytes[0],$1C);
        aWriter.write(ExtraHeaderData[0],Length(ExtraHeaderData));
        for i:=0 to NumRelocs-1 do
          with Relocations[i] do
            begin
              RelocBytes[0]:=Byte(offset);
              RelocBytes[1]:=Byte(offset shr 8);
              RelocBytes[2]:=Byte(segment);
              RelocBytes[3]:=Byte(segment shr 8);
              aWriter.write(RelocBytes[0],4);
            end;
        { pad with zeros until the end of header (paragraph aligned) }
        aWriter.WriteZeros(HeaderSizeInBytes-aWriter.Size);
      end;

    procedure TMZExeHeader.AddRelocation(aSegment, aOffset: Word);
      begin
        SetLength(FRelocations,Length(FRelocations)+1);
        with FRelocations[High(FRelocations)] do
          begin
            segment:=aSegment;
            offset:=aOffset;
          end;
      end;

{****************************************************************************
                               TMZExeSection
****************************************************************************}

    procedure TMZExeSection.AddObjSection(objsec: TObjSection; ignoreprops: boolean);
      begin
        { allow mixing initialized and uninitialized data in the same section
          => set ignoreprops=true }
        inherited AddObjSection(objsec,true);
      end;

{****************************************************************************
                         TMZExeUnifiedLogicalSegment
****************************************************************************}

    constructor TMZExeUnifiedLogicalSegment.create(HashObjectList: TFPHashObjectList; const s: TSymStr);
      var
        Separator: SizeInt;
      begin
        inherited create(HashObjectList,s);
        FObjSectionList:=TFPObjectList.Create(false);
        { name format is 'SegName||ClassName' }
        Separator:=Pos('||',s);
        if Separator>0 then
          begin
            FSegName:=Copy(s,1,Separator-1);
            FSegClass:=Copy(s,Separator+2,Length(s)-Separator-1);
          end
        else
          begin
            FSegName:=Name;
            FSegClass:='';
          end;
        { wlink recognizes the stack segment by the class name 'STACK' }
        { let's be compatible with wlink }
        IsStack:=FSegClass='STACK';
      end;

    destructor TMZExeUnifiedLogicalSegment.destroy;
      begin
        FObjSectionList.Free;
        inherited destroy;
      end;

    procedure TMZExeUnifiedLogicalSegment.AddObjSection(ObjSec: TOmfObjSection);
      begin
        ObjSectionList.Add(ObjSec);
        ObjSec.MZExeUnifiedLogicalSegment:=self;
        { tlink (and ms link?) use the scStack segment combination to recognize
          the stack segment.
          let's be compatible with tlink as well }
        if ObjSec.Combination=scStack then
          IsStack:=True;
      end;

    procedure TMZExeUnifiedLogicalSegment.CalcMemPos;
      var
        MinMemPos: qword=high(qword);
        MaxMemPos: qword=0;
        objsec: TOmfObjSection;
        i: Integer;
      begin
        if ObjSectionList.Count=0 then
          internalerror(2015082201);
        for i:=0 to ObjSectionList.Count-1 do
          begin
            objsec:=TOmfObjSection(ObjSectionList[i]);
            if objsec.MemPos<MinMemPos then
              MinMemPos:=objsec.MemPos;
            if (objsec.MemPos+objsec.Size)>MaxMemPos then
              MaxMemPos:=objsec.MemPos+objsec.Size;
          end;
        MemPos:=MinMemPos;
        Size:=MaxMemPos-MemPos;
      end;

    function TMZExeUnifiedLogicalSegment.MemPosStr: string;
      begin
        Result:=HexStr(MemBasePos shr 4,4)+':'+HexStr((MemPos-MemBasePos),4);
      end;

{****************************************************************************
                         TMZExeUnifiedLogicalGroup
****************************************************************************}

    constructor TMZExeUnifiedLogicalGroup.create(HashObjectList: TFPHashObjectList; const s: TSymStr);
      begin
        inherited create(HashObjectList,s);
        FSegmentList:=TFPHashObjectList.Create(false);
      end;

    destructor TMZExeUnifiedLogicalGroup.destroy;
      begin
        FSegmentList.Free;
        inherited destroy;
      end;

    procedure TMZExeUnifiedLogicalGroup.CalcMemPos;
      var
        MinMemPos: qword=high(qword);
        MaxMemPos: qword=0;
        UniSeg: TMZExeUnifiedLogicalSegment;
        i: Integer;
      begin
        if SegmentList.Count=0 then
          internalerror(2015082201);
        for i:=0 to SegmentList.Count-1 do
          begin
            UniSeg:=TMZExeUnifiedLogicalSegment(SegmentList[i]);
            if UniSeg.MemPos<MinMemPos then
              MinMemPos:=UniSeg.MemPos;
            if (UniSeg.MemPos+UniSeg.Size)>MaxMemPos then
              MaxMemPos:=UniSeg.MemPos+UniSeg.Size;
          end;
        { align *down* on a paragraph boundary }
        MemPos:=(MinMemPos shr 4) shl 4;
        Size:=MaxMemPos-MemPos;
      end;

    function TMZExeUnifiedLogicalGroup.MemPosStr: string;
      begin
        Result:=HexStr(MemPos shr 4,4)+':'+HexStr(MemPos and $f,4);
      end;

    procedure TMZExeUnifiedLogicalGroup.AddSegment(UniSeg: TMZExeUnifiedLogicalSegment);
      begin
        SegmentList.Add(UniSeg.Name,UniSeg);
        if UniSeg.PrimaryGroup='' then
          UniSeg.PrimaryGroup:=Name;
      end;

{****************************************************************************
                               TMZExeOutput
****************************************************************************}

    function TMZExeOutput.GetMZFlatContentSection: TMZExeSection;
      begin
        if not assigned(FMZFlatContentSection) then
          FMZFlatContentSection:=TMZExeSection(FindExeSection('.MZ_flat_content'));
        result:=FMZFlatContentSection;
      end;

    procedure TMZExeOutput.CalcExeUnifiedLogicalSegments;
      var
        ExeSec: TMZExeSection;
        ObjSec: TOmfObjSection;
        UniSeg: TMZExeUnifiedLogicalSegment;
        i: Integer;
      begin
        ExeSec:=MZFlatContentSection;
        for i:=0 to ExeSec.ObjSectionList.Count-1 do
          begin
            ObjSec:=TOmfObjSection(ExeSec.ObjSectionList[i]);
            UniSeg:=TMZExeUnifiedLogicalSegment(ExeUnifiedLogicalSegments.Find(ObjSec.Name));
            if not assigned(UniSeg) then
              UniSeg:=TMZExeUnifiedLogicalSegment.Create(ExeUnifiedLogicalSegments,ObjSec.Name);
            UniSeg.AddObjSection(ObjSec);
          end;
        for i:=0 to ExeUnifiedLogicalSegments.Count-1 do
          begin
            UniSeg:=TMZExeUnifiedLogicalSegment(ExeUnifiedLogicalSegments[i]);
            UniSeg.CalcMemPos;
            if UniSeg.Size>$10000 then
              begin
                if current_settings.x86memorymodel=mm_tiny then
                  Message1(link_e_program_segment_too_large,IntToStr(UniSeg.Size-$10000))
                else if UniSeg.SegClass='CODE' then
                  Message2(link_e_code_segment_too_large,UniSeg.SegName,IntToStr(UniSeg.Size-$10000))
                else if UniSeg.SegClass='DATA' then
                  Message2(link_e_data_segment_too_large,UniSeg.SegName,IntToStr(UniSeg.Size-$10000))
                else
                  Message2(link_e_segment_too_large,UniSeg.SegName,IntToStr(UniSeg.Size-$10000)+' '+UniSeg.SegName);
              end;
          end;
      end;

    procedure TMZExeOutput.CalcExeGroups;

        procedure AddToGroup(UniSeg:TMZExeUnifiedLogicalSegment;GroupName:TSymStr);
          var
            Group: TMZExeUnifiedLogicalGroup;
          begin
            Group:=TMZExeUnifiedLogicalGroup(ExeUnifiedLogicalGroups.Find(GroupName));
            if not assigned(Group) then
              Group:=TMZExeUnifiedLogicalGroup.Create(ExeUnifiedLogicalGroups,GroupName);
            Group.AddSegment(UniSeg);
          end;

      var
        objdataidx,groupidx,secidx: Integer;
        ObjData: TObjData;
        ObjGroup: TObjSectionGroup;
        ObjSec: TOmfObjSection;
        UniGrp: TMZExeUnifiedLogicalGroup;
      begin
        for objdataidx:=0 to ObjDataList.Count-1 do
          begin
            ObjData:=TObjData(ObjDataList[objdataidx]);
            if assigned(ObjData.GroupsList) then
              for groupidx:=0 to ObjData.GroupsList.Count-1 do
                begin
                  ObjGroup:=TObjSectionGroup(ObjData.GroupsList[groupidx]);
                  for secidx:=low(ObjGroup.members) to high(ObjGroup.members) do
                    begin
                      ObjSec:=TOmfObjSection(ObjGroup.members[secidx]);
                      if assigned(ObjSec.MZExeUnifiedLogicalSegment) then
                        AddToGroup(ObjSec.MZExeUnifiedLogicalSegment,ObjGroup.Name);
                    end;
                end;
          end;
        for groupidx:=0 to ExeUnifiedLogicalGroups.Count-1 do
          begin
            UniGrp:=TMZExeUnifiedLogicalGroup(ExeUnifiedLogicalGroups[groupidx]);
            UniGrp.CalcMemPos;
            if UniGrp.Size>$10000 then
              begin
                if current_settings.x86memorymodel=mm_tiny then
                  Message1(link_e_program_segment_too_large,IntToStr(UniGrp.Size-$10000))
                else if UniGrp.Name='DGROUP' then
                  Message2(link_e_data_segment_too_large,UniGrp.Name,IntToStr(UniGrp.Size-$10000))
                else
                  Message2(link_e_group_too_large,UniGrp.Name,IntToStr(UniGrp.Size-$10000));
              end;
          end;
      end;

    procedure TMZExeOutput.CalcSegments_MemBasePos;
      var
        lastbase:qword=0;
        i: Integer;
        UniSeg: TMZExeUnifiedLogicalSegment;
      begin
        for i:=0 to ExeUnifiedLogicalSegments.Count-1 do
          begin
            UniSeg:=TMZExeUnifiedLogicalSegment(ExeUnifiedLogicalSegments[i]);
            if (UniSeg.PrimaryGroup<>'') or (UniSeg.IsStack) or
               (((UniSeg.MemPos+UniSeg.Size-1)-lastbase)>$ffff) then
              lastbase:=(UniSeg.MemPos shr 4) shl 4;
            UniSeg.MemBasePos:=lastbase;
          end;
      end;

    procedure TMZExeOutput.WriteMap_SegmentsAndGroups;
      var
        i: Integer;
        UniSeg: TMZExeUnifiedLogicalSegment;
        UniGrp: TMZExeUnifiedLogicalGroup;
      begin
        exemap.AddHeader('Groups list');
        exemap.Add('');
        exemap.Add(PadSpace('Group',32)+PadSpace('Address',21)+'Size');
        exemap.Add(PadSpace('=====',32)+PadSpace('=======',21)+'====');
        exemap.Add('');
        for i:=0 to ExeUnifiedLogicalGroups.Count-1 do
          begin
            UniGrp:=TMZExeUnifiedLogicalGroup(ExeUnifiedLogicalGroups[i]);
            exemap.Add(PadSpace(UniGrp.Name,32)+PadSpace(UniGrp.MemPosStr,21)+HexStr(UniGrp.Size,8));
          end;
        exemap.Add('');
        exemap.AddHeader('Segments list');
        exemap.Add('');
        exemap.Add(PadSpace('Segment',23)+PadSpace('Class',15)+PadSpace('Group',15)+PadSpace('Address',16)+'Size');
        exemap.Add(PadSpace('=======',23)+PadSpace('=====',15)+PadSpace('=====',15)+PadSpace('=======',16)+'====');
        exemap.Add('');
        for i:=0 to ExeUnifiedLogicalSegments.Count-1 do
          begin
            UniSeg:=TMZExeUnifiedLogicalSegment(ExeUnifiedLogicalSegments[i]);
            exemap.Add(PadSpace(UniSeg.SegName,23)+PadSpace(UniSeg.SegClass,15)+PadSpace(UniSeg.PrimaryGroup,15)+PadSpace(UniSeg.MemPosStr,16)+HexStr(UniSeg.Size,8));
          end;
        exemap.Add('');
      end;

    procedure TMZExeOutput.WriteMap_HeaderData;
      begin
        exemap.AddHeader('Header data');
        exemap.Add('Loadable image size: '+HexStr(Header.LoadableImageSize,8));
        exemap.Add('Min extra paragraphs: '+HexStr(Header.MinExtraParagraphs,4));
        exemap.Add('Max extra paragraphs: '+HexStr(Header.MaxExtraParagraphs,4));
        exemap.Add('Initial stack pointer: '+HexStr(Header.InitialSS,4)+':'+HexStr(Header.InitialSP,4));
        exemap.Add('Entry point address: '+HexStr(Header.InitialCS,4)+':'+HexStr(Header.InitialIP,4));
      end;

    function TMZExeOutput.FindStackSegment: TMZExeUnifiedLogicalSegment;
      var
        i: Integer;
        stackseg_wannabe: TMZExeUnifiedLogicalSegment;
      begin
        Result:=nil;
        for i:=0 to ExeUnifiedLogicalSegments.Count-1 do
          begin
            stackseg_wannabe:=TMZExeUnifiedLogicalSegment(ExeUnifiedLogicalSegments[i]);
            { if there are multiple stack segments, choose the largest one.
              In theory, we're probably supposed to combine them all and put
              them in a contiguous location in memory, but we don't care }
            if stackseg_wannabe.IsStack and
               (not assigned(result) or (Result.Size<stackseg_wannabe.Size)) then
              Result:=stackseg_wannabe;
          end;
      end;

    procedure TMZExeOutput.FillLoadableImageSize;
      var
        i: Integer;
        ExeSec: TMZExeSection;
        ObjSec: TOmfObjSection;
        StartDataPos: LongWord;
        buf: array [0..1023] of byte;
        bytesread: LongWord;
      begin
        Header.LoadableImageSize:=0;
        ExeSec:=MZFlatContentSection;
        for i:=0 to ExeSec.ObjSectionList.Count-1 do
          begin
            ObjSec:=TOmfObjSection(ExeSec.ObjSectionList[i]);
            if (ObjSec.Size>0) and assigned(ObjSec.Data) then
              if (ObjSec.MemPos+ObjSec.Size)>Header.LoadableImageSize then
                Header.LoadableImageSize:=ObjSec.MemPos+ObjSec.Size;
          end;
      end;

    procedure TMZExeOutput.FillMinExtraParagraphs;
      var
        ExeSec: TMZExeSection;
      begin
        ExeSec:=MZFlatContentSection;
        Header.MinExtraParagraphs:=(align(ExeSec.Size,16)-align(Header.LoadableImageSize,16)) div 16;
      end;

    procedure TMZExeOutput.FillMaxExtraParagraphs;
      var
        heapmin_paragraphs: Integer;
        heapmax_paragraphs: Integer;
      begin
        if current_settings.x86memorymodel in x86_far_data_models then
          begin
            { calculate the additional number of paragraphs needed }
            heapmin_paragraphs:=(heapsize + 15) div 16;
            heapmax_paragraphs:=(maxheapsize + 15) div 16;
            Header.MaxExtraParagraphs:=min(Header.MinExtraParagraphs-heapmin_paragraphs+heapmax_paragraphs,$FFFF);
          end
        else
          Header.MaxExtraParagraphs:=$FFFF;
      end;

    procedure TMZExeOutput.FillStartAddress;
      var
        EntryMemPos: qword;
        EntryMemBasePos: qword;
      begin
        EntryMemPos:=EntrySym.address;
        if assigned(EntrySym.group) then
          EntryMemBasePos:=TMZExeUnifiedLogicalGroup(ExeUnifiedLogicalGroups.Find(EntrySym.group.Name)).MemPos
        else
          EntryMemBasePos:=TOmfObjSection(EntrySym.objsection).MZExeUnifiedLogicalSegment.MemBasePos;
        Header.InitialIP:=EntryMemPos-EntryMemBasePos;
        Header.InitialCS:=EntryMemBasePos shr 4;
      end;

    procedure TMZExeOutput.FillStackAddress;
      var
        stackseg: TMZExeUnifiedLogicalSegment;
      begin
        stackseg:=FindStackSegment;
        if assigned(stackseg) then
          begin
            Header.InitialSS:=stackseg.MemBasePos shr 4;
            Header.InitialSP:=stackseg.MemPos+stackseg.Size-stackseg.MemBasePos;
          end
        else
          begin
            Header.InitialSS:=0;
            Header.InitialSP:=0;
          end;
      end;

    procedure TMZExeOutput.FillHeaderData;
      begin
        Header.MaxExtraParagraphs:=$FFFF;
        FillLoadableImageSize;
        FillMinExtraParagraphs;
        FillMaxExtraParagraphs;
        FillStartAddress;
        FillStackAddress;
        if assigned(exemap) then
          WriteMap_HeaderData;
      end;

    function TMZExeOutput.writeExe: boolean;
      var
        ExeSec: TMZExeSection;
        i: Integer;
        ObjSec: TOmfObjSection;
      begin
        Result:=False;
        FillHeaderData;
        Header.WriteTo(FWriter);

        ExeSec:=MZFlatContentSection;
        ExeSec.DataPos:=FWriter.Size;
        for i:=0 to ExeSec.ObjSectionList.Count-1 do
          begin
            ObjSec:=TOmfObjSection(ExeSec.ObjSectionList[i]);
            if ObjSec.MemPos<Header.LoadableImageSize then
              begin
                FWriter.WriteZeros(max(0,ObjSec.MemPos-FWriter.Size+ExeSec.DataPos));
                if assigned(ObjSec.Data) then
                  FWriter.writearray(ObjSec.Data);
              end;
          end;
        Result:=True;
      end;

    function TMZExeOutput.writeCom: boolean;
      const
        ComFileOffset=$100;
      var
        i: Integer;
        ExeSec: TMZExeSection;
        ObjSec: TOmfObjSection;
        StartDataPos: LongWord;
        buf: array [0..1023] of byte;
        bytesread: LongWord;
      begin
        FillHeaderData;
        if Length(Header.Relocations)>0 then
          begin
            Message(link_e_com_program_uses_segment_relocations);
            exit(False);
          end;
        ExeSec:=MZFlatContentSection;
        for i:=0 to ExeSec.ObjSectionList.Count-1 do
          begin
            ObjSec:=TOmfObjSection(ExeSec.ObjSectionList[i]);
            if ObjSec.MemPos<Header.LoadableImageSize then
              begin
                FWriter.WriteZeros(max(0,ObjSec.MemPos-ComFileOffset-FWriter.Size));
                if assigned(ObjSec.Data) then
                  begin
                    if ObjSec.MemPos<ComFileOffset then
                      begin
                        ObjSec.Data.seek(ComFileOffset-ObjSec.MemPos);
                        repeat
                          bytesread:=ObjSec.Data.read(buf,sizeof(buf));
                          if bytesread<>0 then
                            FWriter.write(buf,bytesread);
                        until bytesread=0;
                      end
                    else
                      FWriter.writearray(ObjSec.Data);
                  end;
              end;
          end;
        Result:=True;
      end;

    function TMZExeOutput.writeDebugElf: boolean;
      label
        cleanup;
      var
        debugsections: array of TMZExeSection;
        debugsections_count: Word;
        elfsections_count: Word;
        elfsechdrs: array of TElf32sechdr;
        shstrndx: Word;
        next_section_ofs: LongWord;
        ElfHeader: TElf32header;
        shstrtabsect_data: TDynamicArray=Nil;
        I, elfsecidx, J: Integer;
        ObjSec: TOmfObjSection;
      begin
        { count the debug sections }
        debugsections_count:=0;
        for I:=0 to ExeSectionList.Count-1 do
          if oso_debug in TMZExeSection(ExeSectionList[I]).SecOptions then
            Inc(debugsections_count);

        { extract them into the debugsections array }
        SetLength(debugsections,debugsections_count);
        debugsections_count:=0;
        for I:=0 to ExeSectionList.Count-1 do
          if oso_debug in TMZExeSection(ExeSectionList[I]).SecOptions then
            begin
              debugsections[debugsections_count]:=TMZExeSection(ExeSectionList[I]);
              Inc(debugsections_count);
            end;

        { prepare/allocate elf section headers }
        elfsections_count:=debugsections_count+2;
        SetLength(elfsechdrs,elfsections_count);
        for I:=0 to elfsections_count-1 do
          FillChar(elfsechdrs[I],SizeOf(elfsechdrs[I]),0);
        shstrndx:=elfsections_count-1;
        shstrtabsect_data:=tdynamicarray.Create(SectionDataMaxGrow);
        shstrtabsect_data.writestr(#0);
        next_section_ofs:=SizeOf(ElfHeader)+elfsections_count*SizeOf(TElf32sechdr);
        for I:=0 to debugsections_count-1 do
          begin
            elfsecidx:=I+1;
            with elfsechdrs[elfsecidx] do
              begin
                sh_name:=shstrtabsect_data.Pos;
                sh_type:=SHT_PROGBITS;
                sh_flags:=0;
                sh_addr:=0;
                sh_offset:=next_section_ofs;
                sh_size:=debugsections[I].Size;
                sh_link:=0;
                sh_info:=0;
                sh_addralign:=0;
                sh_entsize:=0;
              end;
            Inc(next_section_ofs,debugsections[I].Size);
            shstrtabsect_data.writestr(debugsections[I].Name+#0);
          end;
        with elfsechdrs[shstrndx] do
          begin
            sh_name:=shstrtabsect_data.Pos;
            shstrtabsect_data.writestr('.shstrtab'#0);
            sh_type:=SHT_STRTAB;
            sh_flags:=0;
            sh_addr:=0;
            sh_offset:=next_section_ofs;
            sh_size:=shstrtabsect_data.Size;
            sh_link:=0;
            sh_info:=0;
            sh_addralign:=0;
            sh_entsize:=0;
          end;

        { write header }
        FillChar(ElfHeader,SizeOf(ElfHeader),0);
        ElfHeader.e_ident[EI_MAG0]:=ELFMAG0; { = #127'ELF' }
        ElfHeader.e_ident[EI_MAG1]:=ELFMAG1;
        ElfHeader.e_ident[EI_MAG2]:=ELFMAG2;
        ElfHeader.e_ident[EI_MAG3]:=ELFMAG3;
        ElfHeader.e_ident[EI_CLASS]:=ELFCLASS32;
        ElfHeader.e_ident[EI_DATA]:=ELFDATA2LSB;
        ElfHeader.e_ident[EI_VERSION]:=1;
        ElfHeader.e_ident[EI_OSABI]:=ELFOSABI_NONE;
        ElfHeader.e_ident[EI_ABIVERSION]:=0;
        ElfHeader.e_type:=ET_EXEC;
        ElfHeader.e_machine:=EM_386;
        ElfHeader.e_version:=1;
        ElfHeader.e_entry:=0;
        ElfHeader.e_phoff:=0;
        ElfHeader.e_shoff:=SizeOf(ElfHeader);
        ElfHeader.e_flags:=0;
        ElfHeader.e_ehsize:=SizeOf(ElfHeader);
        ElfHeader.e_phentsize:=SizeOf(TElf32proghdr);
        ElfHeader.e_phnum:=0;
        ElfHeader.e_shentsize:=SizeOf(TElf32sechdr);
        ElfHeader.e_shnum:=elfsections_count;
        ElfHeader.e_shstrndx:=shstrndx;
        MaybeSwapHeader(ElfHeader);
        Writer.write(ElfHeader,sizeof(ElfHeader));

        { write section headers }
        for I:=0 to elfsections_count-1 do
          begin
            MaybeSwapSecHeader(elfsechdrs[I]);
            Writer.write(elfsechdrs[I],SizeOf(elfsechdrs[I]));
          end;

        { write section data }
        for J:=0 to debugsections_count-1 do
          begin
            debugsections[J].DataPos:=Writer.Size;
            for i:=0 to debugsections[J].ObjSectionList.Count-1 do
              begin
                ObjSec:=TOmfObjSection(debugsections[J].ObjSectionList[i]);
                if ObjSec.MemPos<Header.LoadableImageSize then
                  begin
                    FWriter.WriteZeros(max(0,ObjSec.MemPos-FWriter.Size+debugsections[J].DataPos));
                    if assigned(ObjSec.Data) then
                      FWriter.writearray(ObjSec.Data);
                  end;
              end;
          end;
        { write .shstrtab section data }
        Writer.writearray(shstrtabsect_data);

        Result:=True;
cleanup:
        shstrtabsect_data.Free;
      end;

    procedure TMZExeOutput.Load_Symbol(const aname: string);
      var
        dgroup: TObjSectionGroup;
        sym: TObjSymbol;
      begin
        { special handling for the '_edata' and '_end' symbols, which are
          internally added by the linker }
        if (aname='_edata') or (aname='_end') then
          begin
            { create an internal segment with the 'BSS' class }
            internalObjData.createsection('*'+aname+'||BSS',0,[]);
            { add to group 'DGROUP' }
            dgroup:=nil;
            if assigned(internalObjData.GroupsList) then
              dgroup:=TObjSectionGroup(internalObjData.GroupsList.Find('DGROUP'));
            if dgroup=nil then
              dgroup:=internalObjData.createsectiongroup('DGROUP');
            SetLength(dgroup.members,Length(dgroup.members)+1);
            dgroup.members[Length(dgroup.members)-1]:=internalObjData.CurrObjSec;
            { define the symbol itself }
            sym:=internalObjData.SymbolDefine(aname,AB_GLOBAL,AT_DATA);
            sym.group:=dgroup;
          end
        else
          inherited;
      end;

    procedure TMZExeOutput.DoRelocationFixup(objsec: TObjSection);
      var
        i: Integer;
        omfsec: TOmfObjSection absolute objsec;
        objreloc: TOmfRelocation;
        target: DWord;
        framebase: DWord;
        fixupamount: Integer;
        target_group: TMZExeUnifiedLogicalGroup;

        procedure FixupOffset;
          var
            w: Word;
          begin
            omfsec.Data.seek(objreloc.DataOffset);
            omfsec.Data.read(w,2);
            w:=LEtoN(w);
            Inc(w,fixupamount);
            w:=LEtoN(w);
            omfsec.Data.seek(objreloc.DataOffset);
            omfsec.Data.write(w,2);
          end;

        procedure FixupOffset32;
          var
            lw: LongWord;
          begin
            omfsec.Data.seek(objreloc.DataOffset);
            omfsec.Data.read(lw,4);
            lw:=LEtoN(lw);
            Inc(lw,fixupamount);
            lw:=LEtoN(lw);
            omfsec.Data.seek(objreloc.DataOffset);
            omfsec.Data.write(lw,4);
          end;

        procedure FixupBase(DataOffset: LongWord);
          var
            w: Word;
          begin
            omfsec.Data.seek(DataOffset);
            omfsec.Data.read(w,2);
            w:=LEtoN(w);
            Inc(w,framebase shr 4);
            w:=LEtoN(w);
            omfsec.Data.seek(DataOffset);
            omfsec.Data.write(w,2);
            Header.AddRelocation(omfsec.MZExeUnifiedLogicalSegment.MemBasePos shr 4,
              omfsec.MemPos+DataOffset-omfsec.MZExeUnifiedLogicalSegment.MemBasePos);
          end;

      begin
        for i:=0 to objsec.ObjRelocations.Count-1 do
          begin
            objreloc:=TOmfRelocation(objsec.ObjRelocations[i]);
            if assigned(objreloc.symbol) then
              begin
                target:=objreloc.symbol.address;
                if objreloc.FrameGroup<>'' then
                  framebase:=TMZExeUnifiedLogicalGroup(ExeUnifiedLogicalGroups.Find(objreloc.FrameGroup)).MemPos
                else if assigned(objreloc.symbol.group) then
                  framebase:=TMZExeUnifiedLogicalGroup(ExeUnifiedLogicalGroups.Find(objreloc.symbol.group.Name)).MemPos
                else
                  framebase:=TOmfObjSection(objreloc.symbol.objsection).MZExeUnifiedLogicalSegment.MemBasePos;
                case objreloc.typ of
                  RELOC_ABSOLUTE16,RELOC_ABSOLUTE32,RELOC_SEG,RELOC_FARPTR,RELOC_FARPTR48:
                    fixupamount:=target-framebase;
                  RELOC_RELATIVE16,RELOC_SEGREL,RELOC_FARPTR_RELATIVEOFFSET:
                    fixupamount:=target-(omfsec.MemPos+objreloc.DataOffset)-2;
                  RELOC_RELATIVE32,RELOC_FARPTR48_RELATIVEOFFSET:
                    fixupamount:=target-(omfsec.MemPos+objreloc.DataOffset)-4;
                  else
                    internalerror(2015082402);
                end;
                case objreloc.typ of
                  RELOC_ABSOLUTE16,
                  RELOC_RELATIVE16:
                    FixupOffset;
                  RELOC_ABSOLUTE32,
                  RELOC_RELATIVE32:
                    FixupOffset32;
                  RELOC_SEG,
                  RELOC_SEGREL:
                    FixupBase(objreloc.DataOffset);
                  RELOC_FARPTR,
                  RELOC_FARPTR_RELATIVEOFFSET:
                    begin
                      FixupOffset;
                      FixupBase(objreloc.DataOffset+2);
                    end;
                  RELOC_FARPTR48,
                  RELOC_FARPTR48_RELATIVEOFFSET:
                    begin
                      FixupOffset32;
                      FixupBase(objreloc.DataOffset+4);
                    end;
                  else
                    internalerror(2015082403);
                end;
              end
            else if assigned(objreloc.objsection) then
              begin
                target:=objreloc.objsection.MemPos;
                if objreloc.FrameGroup<>'' then
                  framebase:=TMZExeUnifiedLogicalGroup(ExeUnifiedLogicalGroups.Find(objreloc.FrameGroup)).MemPos
                else
                  framebase:=TOmfObjSection(objreloc.objsection).MZExeUnifiedLogicalSegment.MemBasePos;
                case objreloc.typ of
                  RELOC_ABSOLUTE16,RELOC_ABSOLUTE32,RELOC_SEG,RELOC_FARPTR,RELOC_FARPTR48:
                    fixupamount:=target-framebase;
                  RELOC_RELATIVE16,RELOC_SEGREL,RELOC_FARPTR_RELATIVEOFFSET:
                    fixupamount:=target-(omfsec.MemPos+objreloc.DataOffset)-2;
                  RELOC_RELATIVE32,RELOC_FARPTR48_RELATIVEOFFSET:
                    fixupamount:=target-(omfsec.MemPos+objreloc.DataOffset)-4;
                  else
                    internalerror(2015082405);
                end;
                case objreloc.typ of
                  RELOC_ABSOLUTE16,
                  RELOC_RELATIVE16:
                    FixupOffset;
                  RELOC_ABSOLUTE32,
                  RELOC_RELATIVE32:
                    FixupOffset32;
                  RELOC_SEG,
                  RELOC_SEGREL:
                    FixupBase(objreloc.DataOffset);
                  RELOC_FARPTR,
                  RELOC_FARPTR_RELATIVEOFFSET:
                    begin
                      FixupOffset;
                      FixupBase(objreloc.DataOffset+2);
                    end;
                  RELOC_FARPTR48,
                  RELOC_FARPTR48_RELATIVEOFFSET:
                    begin
                      FixupOffset32;
                      FixupBase(objreloc.DataOffset+4);
                    end;
                  else
                    internalerror(2015082406);
                end;
              end
            else if assigned(objreloc.group) then
              begin
                target_group:=TMZExeUnifiedLogicalGroup(ExeUnifiedLogicalGroups.Find(objreloc.group.Name));
                target:=target_group.MemPos;
                if objreloc.FrameGroup<>'' then
                  framebase:=TMZExeUnifiedLogicalGroup(ExeUnifiedLogicalGroups.Find(objreloc.FrameGroup)).MemPos
                else
                  framebase:=target_group.MemPos;
                case objreloc.typ of
                  RELOC_ABSOLUTE16,RELOC_ABSOLUTE32,RELOC_SEG,RELOC_FARPTR,RELOC_FARPTR48:
                    fixupamount:=target-framebase;
                  RELOC_RELATIVE16,RELOC_SEGREL,RELOC_FARPTR_RELATIVEOFFSET:
                    fixupamount:=target-(omfsec.MemPos+objreloc.DataOffset)-2;
                  RELOC_RELATIVE32,RELOC_FARPTR48_RELATIVEOFFSET:
                    fixupamount:=target-(omfsec.MemPos+objreloc.DataOffset)-4;
                  else
                    internalerror(2015111202);
                end;
                case objreloc.typ of
                  RELOC_ABSOLUTE16,
                  RELOC_RELATIVE16:
                    FixupOffset;
                  RELOC_ABSOLUTE32,
                  RELOC_RELATIVE32:
                    FixupOffset32;
                  RELOC_SEG,
                  RELOC_SEGREL:
                    FixupBase(objreloc.DataOffset);
                  RELOC_FARPTR,
                  RELOC_FARPTR_RELATIVEOFFSET:
                    begin
                      FixupOffset;
                      FixupBase(objreloc.DataOffset+2);
                    end;
                  RELOC_FARPTR48,
                  RELOC_FARPTR48_RELATIVEOFFSET:
                    begin
                      FixupOffset32;
                      FixupBase(objreloc.DataOffset+4);
                    end;
                  else
                    internalerror(2015111203);
                end;
              end
            else
              internalerror(2015082407);
          end;
      end;

    function IOmfObjSectionClassNameCompare(Item1, Item2: Pointer): Integer;
      var
        I1 : TOmfObjSection absolute Item1;
        I2 : TOmfObjSection absolute Item2;
      begin
        Result:=CompareStr(I1.ClassName,I2.ClassName);
        if Result=0 then
          Result:=CompareStr(I1.Name,I2.Name);
        if Result=0 then
          Result:=I1.SortOrder-I2.SortOrder;
      end;

    procedure TMZExeOutput.Order_ObjSectionList(ObjSectionList: TFPObjectList; const aPattern: string);
      var
        i: Integer;
      begin
        for i:=0 to ObjSectionList.Count-1 do
          TOmfObjSection(ObjSectionList[i]).SortOrder:=i;
        ObjSectionList.Sort(@IOmfObjSectionClassNameCompare);
      end;

    procedure TMZExeOutput.MemPos_EndExeSection;
      var
        SecName: TSymStr='';
      begin
        if assigned(CurrExeSec) then
          SecName:=CurrExeSec.Name;
        inherited MemPos_EndExeSection;
        if SecName='.MZ_flat_content' then
          begin
            CalcExeUnifiedLogicalSegments;
            CalcExeGroups;
            CalcSegments_MemBasePos;
            if assigned(exemap) then
              WriteMap_SegmentsAndGroups;
          end;
      end;

    function TMZExeOutput.writeData: boolean;
      begin
        Result:=False;
        if ExeWriteMode in [ewm_exefull,ewm_exeonly] then
          begin
            if apptype=app_com then
              Result:=WriteCom
            else
              Result:=WriteExe;
            if not Result then
              exit;
          end;
        if ((cs_debuginfo in current_settings.moduleswitches) and
            (target_dbg.id in [dbg_dwarf2,dbg_dwarf3,dbg_dwarf4])) and
           ((ExeWriteMode=ewm_dbgonly) or
            ((ExeWriteMode=ewm_exefull) and
              not(cs_link_strip in current_settings.globalswitches))) then
          Result:=writeDebugElf;
      end;

    constructor TMZExeOutput.create;
      begin
        inherited create;
        CExeSection:=TMZExeSection;
        CObjData:=TOmfObjData;
        CObjSymbol:=TOmfObjSymbol;
        { "640K ought to be enough for anybody" :) }
        MaxMemPos:=$9FFFF;
        FExeUnifiedLogicalSegments:=TFPHashObjectList.Create;
        FExeUnifiedLogicalGroups:=TFPHashObjectList.Create;
        FHeader:=TMZExeHeader.Create;
      end;

    destructor TMZExeOutput.destroy;
      begin
        FHeader.Free;
        FExeUnifiedLogicalGroups.Free;
        FExeUnifiedLogicalSegments.Free;
        inherited destroy;
      end;

{****************************************************************************
                               TOmfAssembler
****************************************************************************}

    constructor TOmfAssembler.Create(info: pasminfo; smart:boolean);
      begin
        inherited;
        CObjOutput:=TOmfObjOutput;
        CInternalAr:=TOmfLibObjectWriter;
      end;

{*****************************************************************************
                                  Initialize
*****************************************************************************}
{$ifdef i8086}
    const
       as_i8086_omf_info : tasminfo =
          (
            id     : as_i8086_omf;
            idtxt  : 'OMF';
            asmbin : '';
            asmcmd : '';
            supported_targets : [system_i8086_msdos,system_i8086_embedded];
            flags : [af_outputbinary,af_smartlink_sections];
            labelprefix : '..@';
            comment : '; ';
            dollarsign: '$';
          );
{$endif i8086}

initialization
{$ifdef i8086}
  RegisterAssembler(as_i8086_omf_info,TOmfAssembler);
{$endif i8086}
end.