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+ MIPS linker: support linking PIC object files with non-PIC ones, by routing absolute calls into PIC code through stubs that load R25.
git-svn-id: trunk@24098 -
This commit is contained in:
sergei
parent
9758f4fa6a
commit
cded05ccef
@ -43,7 +43,13 @@ implementation
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local_got_relocs: TFPObjectList;
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local_got_slots: TFPHashObjectList;
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got_content: array of pint;
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procedure MaybeWriteGOTEntry(reltyp:byte;relocval:aint;objsym:TObjSymbol);
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pic_stub_syms: TFPObjectList;
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pic_stubs: THashSet;
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nullstub: TObjSymbol;
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stubcount: longint;
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trampolinesection: TObjSection;
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procedure MaybeWriteGOTEntry(relocval:aint;objsym:TObjSymbol);
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procedure CreatePICStub(objsym:TObjSymbol);
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protected
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procedure PrepareGOT;override;
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function AllocGOTSlot(objsym:TObjSymbol):boolean;override;
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@ -163,6 +169,10 @@ implementation
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ri_gp_value: longint; // signed
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end;
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TStubHashKey=record
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objsec:TObjSection;
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offset:aword;
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end;
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procedure MaybeSwapElfReginfo(var h:TElfReginfo);
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var
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@ -234,6 +244,8 @@ implementation
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begin
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inherited Create;
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local_got_relocs:=TFPObjectList.Create(False);
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pic_stub_syms:=TFPObjectList.Create(False);
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pic_stubs:=THashSet.Create(64,True,False);
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local_got_slots:=TFPHashObjectList.Create(True);
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end;
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@ -241,6 +253,8 @@ implementation
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destructor TElfExeOutputMIPS.Destroy;
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begin
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local_got_slots.Free;
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pic_stub_syms.Free;
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pic_stubs.Free;
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local_got_relocs.Free;
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inherited Destroy;
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end;
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@ -248,6 +262,10 @@ implementation
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procedure TElfExeOutputMIPS.CreateGOTSection;
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begin
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nullstub:=TObjSymbol.Create(internalobjdata.ObjSymbolList,'*null_pic_stub*');
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nullstub.bind:=AB_LOCAL;
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nullstub.typ:=AT_FUNCTION;
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gotobjsec:=TElfObjSection.create_ext(internalObjData,'.got',
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SHT_PROGBITS,SHF_ALLOC or SHF_WRITE or SHF_MIPS_GPREL,sizeof(pint),sizeof(pint));
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gotobjsec.SecOptions:=[oso_keep];
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@ -355,11 +373,33 @@ implementation
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var
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i: longint;
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exesym: TExeSymbol;
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exesec: TExeSection;
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newsec,objsec:TObjSection;
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list:TFPObjectList;
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begin
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inherited PrepareGOT;
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{ !! maybe incorrect, where do 'unmapped globals' belong? }
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dt_local_gotno_value:=gotobjsec.size div sizeof(pint);
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{ Insert PIC stubs (slow...) }
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if assigned(trampolinesection) then
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begin
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exesec:=FindExeSection('.text');
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exesec.ObjSectionList.Add(trampolinesection);
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trampolinesection.ExeSection:=exesec;
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trampolinesection.Used:=true;
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end;
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for i:=0 to pic_stub_syms.count-1 do
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begin
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exesym:=TExeSymbol(pic_stub_syms[i]);
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newsec:=exesym.stubsymbol.objsection;
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objsec:=exesym.objsymbol.objsection;
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list:=objsec.ExeSection.ObjSectionList;
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list.insert(list.IndexOf(objsec),newsec);
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newsec.ExeSection:=objsec.ExeSection;
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newsec.Used:=true;
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end;
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if not dynamiclink then
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exit;
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{ make room for first R_MIPS_NONE entry }
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@ -496,7 +536,7 @@ implementation
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gotobjsec.writeZeros(gotsize-gotobjsec.size);
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end;
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procedure TElfExeOutputMIPS.MaybeWriteGOTEntry(reltyp:byte;relocval:aint;objsym:TObjSymbol);
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procedure TElfExeOutputMIPS.MaybeWriteGOTEntry(relocval:aint;objsym:TObjSymbol);
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var
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gotoff:aword;
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begin
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@ -515,6 +555,46 @@ implementation
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end;
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end;
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procedure TElfExeOutputMIPS.CreatePICStub(objsym:TObjSymbol);
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var
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textsec,newsec:TObjSection;
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newsym:TObjSymbol;
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use_trampoline:boolean;
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begin
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textsec:=objsym.objsection;
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use_trampoline:=(objsym.offset>0) or (textsec.SecAlign>16);
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if use_trampoline then
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begin
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if trampolinesection=nil then
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trampolinesection:=internalObjData.createsection(sec_code);
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newsec:=trampolinesection;
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end
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else
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begin
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inc(stubcount);
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newsec:=TElfObjSection.create_ext(internalObjData,'.text.stub.'+tostr(stubcount),
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SHT_PROGBITS,SHF_ALLOC or SHF_EXECINSTR,0,textsec.SecAlign);
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if (newsec.SecAlign>8) then
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newsec.WriteZeros(newsec.SecAlign-8);
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pic_stub_syms.add(objsym.ExeSymbol);
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end;
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{ symbol for the stub }
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internalObjData.SetSection(newsec);
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newsym:=internalObjData.symboldefine('.pic.'+objsym.name,AB_LOCAL,AT_FUNCTION);
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putword(newsec,$3c190000); // lui $t9,%hi(x)
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newsec.addrawreloc(newsec.size-4,objsym,R_MIPS_HI16);
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if use_trampoline then
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begin
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putword(newsec,$08000000); // j x
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newsec.addrawreloc(newsec.size-4,objsym,R_MIPS_26);
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end;
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putword(newsec,$27390000); // addiu $t9,$t9,%lo(x)
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newsec.addrawreloc(newsec.size-4,objsym,R_MIPS_LO16);
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objsym.exesymbol.stubsymbol:=newsym;
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end;
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procedure TElfExeOutputMIPS.GOTRelocPass1(objsec:TObjSection;var idx:longint);
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var
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objreloc:TObjRelocation;
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@ -524,6 +604,12 @@ implementation
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found:boolean;
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i:longint;
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lopart,hipart:longword;
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objdata:TElfObjData;
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exesym:TExeSymbol;
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targetsec:TObjSection;
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tmp:array[0..2] of longword;
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key:TStubHashKey;
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entry:PHashSetItem;
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begin
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objreloc:=TObjRelocation(objsec.ObjRelocations[idx]);
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if (ObjReloc.flags and rf_raw)=0 then
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@ -547,6 +633,59 @@ implementation
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end
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end;
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R_MIPS_PC16,
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R_MIPS_26:
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begin
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{ Absolute calls into PIC code must go through stubs that load R25 }
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exesym:=objreloc.symbol.exesymbol;
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if (exesym=nil) or (exesym.dynindex<>0) then
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exit;
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{ Stub already created? Redirect to it and be done. }
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if assigned(exesym.stubsymbol) then
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begin
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if (exesym.stubsymbol<>nullstub) then
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begin
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objreloc.symbol.offset:=exesym.stubsymbol.offset;
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objreloc.symbol.objsection:=exesym.stubsymbol.objsection;
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end;
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exit;
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end;
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targetsec:=exesym.ObjSymbol.objsection;
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objdata:=TElfObjData(targetsec.ObjData);
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if (objdata.flags and EF_MIPS_PIC)=0 then
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exit;
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{ Same objdata? then it's responsibility of assembler, not linker }
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if (objdata=objsec.objdata) then
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exit;
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{ Check if destination begins with PIC prologue. If not, mark symbol
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with 'null' stub so we don't waste time on subsequent relocs to it. }
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targetsec.data.seek(exesym.ObjSymbol.offset);
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targetsec.data.read(tmp,3*sizeof(longword));
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if (source_info.endian<>target_info.endian) then
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for i:=0 to 2 do
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tmp[i]:=swapendian(tmp[i]);
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if ((tmp[0] and $FFFF0000)<>$3C1C0000) or
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((tmp[1] and $FFFF0000)<>$279C0000) or
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(tmp[2]<>$0399E021) then
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begin
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exesym.stubsymbol:=nullstub;
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exit;
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end;
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{ Avoid creating several stubs for an address due to symbol aliasing }
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key.objsec:=targetsec;
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key.offset:=exesym.ObjSymbol.offset;
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entry:=pic_stubs.FindOrAdd(@key,sizeof(TStubHashKey));
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if assigned(entry^.Data) then
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exesym:=TExeSymbol(entry^.Data)
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else
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begin
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entry^.Data:=exesym;
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CreatePICStub(exesym.objsymbol);
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end;
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objreloc.symbol.offset:=exesym.stubsymbol.offset;
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objreloc.symbol.objsection:=exesym.stubsymbol.objsection;
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end;
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R_MIPS_CALL16,
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R_MIPS_GOT16:
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begin
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@ -768,7 +907,7 @@ implementation
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reloclist:=hr;
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continue;
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end;
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MaybeWriteGOTEntry(reltyp,relocval,objreloc.symbol);
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MaybeWriteGOTEntry(relocval,objreloc.symbol);
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// !! this is correct only while _gp symbol is defined relative to .got !!
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relocval:=-(gotsymbol.offset-(objreloc.symbol.exesymbol.gotoffset-sizeof(pint)));
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// TODO: check overflow
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@ -400,6 +400,13 @@ interface
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{ fields for ELF linking }
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gotoffset : aword;
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dynindex : aword;
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{ A thunk used to redirect some references to symbol (like absolute
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jumps/calls to PIC code).
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This probably is also needed for ARM/Thumb interworking and alike.
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TODO: consider reusing objsymbol.indsymbol for this purpose }
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{$ifdef mips}
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stubsymbol : TObjSymbol;
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{$endif mips}
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end;
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TExeSection = class(TFPHashObject)
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