mirror of
https://github.com/autc04/Retro68.git
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305 lines
10 KiB
C++
305 lines
10 KiB
C++
/*
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Copyright 2017 Wolfgang Thaller.
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This file is part of Retro68.
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Retro68 is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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Retro68 is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with Retro68. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "Section.h"
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#include "Symbol.h"
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#include "Reloc.h"
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#include "Object.h"
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#include "Symtab.h"
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#include <algorithm>
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#include <sstream>
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#include <assert.h>
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#include <iostream>
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#include "BinaryIO.h"
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using std::string;
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Section::~Section()
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{
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}
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Section::Section(Object& theObject, string name, int idx, SectionKind kind, Elf_Scn *elfsec)
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: theObject(theObject),
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name(name), idx(idx), kind(kind), elfsec(elfsec), relasec(NULL),
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exceptionInfoStart(0),
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codeID(-1), firstJTEntryIndex(0)
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{
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data = elf_getdata(elfsec, NULL);
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gelf_getshdr(elfsec, &shdr);
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outputBase = shdr.sh_addr;
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}
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void Section::SetRela(Elf_Scn *scn)
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{
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relasec = scn;
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GElf_Shdr rshdr;
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gelf_getshdr(relasec, &rshdr);
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int nRela = rshdr.sh_size / rshdr.sh_entsize;
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Elf_Data *data = elf_getdata(relasec, NULL);
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for(int i = 0; i < nRela; i++)
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{
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GElf_Rela rela;
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gelf_getrela(data, i, &rela);
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if(rela.r_offset < shdr.sh_addr || rela.r_offset > shdr.sh_addr + shdr.sh_size - 4)
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{
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// FIXME: There are sometimes relocations beyond the end of the sections
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// in LD output for some reason. That's bad. Let's ignore it.
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continue;
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}
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relocs.push_back(rela);
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}
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std::sort(relocs.begin(), relocs.end(),
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[](GElf_Rela& a, GElf_Rela& b) { return a.r_offset < b.r_offset; });
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}
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uint32_t Section::GetSize()
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{
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return data->d_size;
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}
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string Section::GetData()
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{
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return string((char*)data->d_buf, (char*)data->d_buf + data->d_size);
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}
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std::vector<RuntimeReloc> Section::GetRelocations(bool useOffsets)
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{
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std::vector<RuntimeReloc> outRelocs;
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for(auto& rela : relocs)
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{
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//printf("rel: %d %d %x %x\n", (int)GELF_R_TYPE(rela.r_info), (int)GELF_R_SYM(rela.r_info), (unsigned)rela.r_addend, (unsigned)rela.r_offset);
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int symidx = GELF_R_SYM(rela.r_info);
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if(symidx == 0)
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continue;
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Symbol& sym = theObject.symtab->GetSym(symidx);
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if(sym.st_shndx == SHN_UNDEF || sym.st_shndx >= SHN_LORESERVE)
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continue;
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if(sym.sectionKind == SectionKind::undefined)
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continue;
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uint32_t offset = rela.r_offset;
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if(useOffsets)
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offset -= shdr.sh_addr;
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if(GELF_R_TYPE(rela.r_info) == R_68K_32)
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{
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outRelocs.emplace_back(rela.relocBase, offset);
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}
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if(GELF_R_TYPE(rela.r_info) == R_68K_PC32
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&& sym.st_shndx != idx)
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{
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outRelocs.emplace_back(rela.relocBase, offset, true);
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}
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}
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return outRelocs;
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}
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void Section::ScanRelocs()
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{
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for(Reloc& rela : relocs)
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{
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int symidx = GELF_R_SYM(rela.r_info);
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if(symidx == 0)
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continue;
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Symbol *sym = &theObject.symtab->GetSym(symidx);
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if(sym->st_shndx == SHN_UNDEF)
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continue;
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if(rela.r_addend != 0)
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{
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int symidx2 = theObject.symtab->FindSym(sym->st_shndx, sym->st_value + rela.r_addend);
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if(symidx2 != -1)
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{
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sym = &theObject.symtab->GetSym(symidx2);
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rela.r_addend = 0;
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rela.r_info = GELF_R_INFO(symidx2, GELF_R_TYPE(rela.r_info));
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}
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}
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if(sym->st_shndx != idx)
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sym->referencedExternally = true;
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}
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}
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void Section::FixRelocs(bool allowDirectCodeRefs)
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{
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for(Reloc& rela : relocs)
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{
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if(GELF_R_TYPE(rela.r_info) != R_68K_32 && GELF_R_TYPE(rela.r_info) != R_68K_PC32)
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continue;
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int symidx = GELF_R_SYM(rela.r_info);
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if(symidx == 0)
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continue;
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Symbol& sym = theObject.symtab->GetSym(symidx);
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if(sym.sectionKind == SectionKind::undefined)
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continue;
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if(GELF_R_TYPE(rela.r_info) == R_68K_PC32 && sym.st_shndx == idx)
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continue;
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RelocBase relocBase;
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switch(sym.sectionKind)
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{
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case SectionKind::code:
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relocBase = RelocBase::code;
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if(exceptionInfoStart != 0 && rela.r_offset >= exceptionInfoStart
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&& sym.name != "__gxx_personality_v0")
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{
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// Case 1:
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// references from .eh_frame, with the exception of __gcc_personality_v0.
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// Should be direct references within the code segment.
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if(sym.section.get() != this)
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{
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#if 0
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std::cerr << "Warning: clearing cross-segment reference from .eh_frame:\n"
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<< sym.name << " (" << name << "->" << sym.section->name << ")\n";
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std::cerr << std::hex << (int)sym.st_info << " " << (int)sym.st_other << std::endl;
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//assert(GELF_ST_BIND(sym.st_info) == STB_WEAK);
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#endif
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/*
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ld behaves differently depending on whether debug info is present.
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If debug info is present, .eh_frame sections will contain references
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to other code segments, if no debug info is generated (or it is
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stripped at link time), then these pointers are set to 0 during linking.
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In most cases, this has to do with weak symbols; the instance of the
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symbol that is removed gets a null ptr (with R_68K_NONE relocation) in
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the .eh_frame section if there is no debug info, but gets remapped to
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the surviving instance if there is debug info.
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It also happens with some section symbols, and I *hope* this is related.
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This makes no sense to me, but the reason is probably buried somewhere
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within a 900-line function of C code within a 15000 line source file
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in GNU bfd.
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I *hope* that the correct behavior is to just clear those pointers.
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*/
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uint8_t *relocand = ((uint8_t*) data->d_buf + rela.r_offset - shdr.sh_addr);
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relocand[0] = relocand[1] = relocand[2] = relocand[3] = 0;
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rela.r_info = 0;
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}
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}
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else if(sym.needsJT)
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{
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// Case 2: References to code that can go through the jump table.
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// If we need an addend, that's a problem and we abort.
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if(rela.r_addend == 0)
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{
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relocBase = RelocBase::jumptable;
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}
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else
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{
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if(sym.section.get() != this)
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{
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std::cerr << "Invalid ref from "
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<< name << ":" << std::hex << rela.r_offset-shdr.sh_addr << std::dec
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<< " to " << sym.section->name
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<< "(" << sym.name << ")"
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<< "+" << rela.r_offset << std::endl;
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}
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assert(sym.section.get() == this);
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}
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}
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else if(allowDirectCodeRefs)
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{
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// Case 3: Direct Code Refs are allowed (single-segment exectuable),
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// We are happy. Nothing to check or do.
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}
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else
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{
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// Case 4: Multi-segment executable.
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// Code references that don't go through the jump table
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// must remain in the current segment.
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if(sym.section.get() != this)
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{
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// Should never happen because symbols that are referenced from a different
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// segment get their needsJT flag set (ScanRelocs and Obejct::MultiSegmentApp).
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std::cerr << "Invalid ref from "
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<< name << ":" << std::hex << rela.r_offset-shdr.sh_addr << std::dec
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<< " to " << sym.section->name
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<< "(" << sym.name << ")"
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<< "+" << rela.r_offset << std::endl;
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std::cerr << "needsJT: " << (sym.needsJT ? "true" : "false") << std::endl;
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std::cerr << "from addr: " << rela.r_offset << ", exceptionInfoStart: " << exceptionInfoStart << std::endl;
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}
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assert(sym.section.get() == this);
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}
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break;
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case SectionKind::data:
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relocBase = RelocBase::data;
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break;
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case SectionKind::bss:
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relocBase = RelocBase::bss;
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break;
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case SectionKind::undefined:
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assert(false);
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break;
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}
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if(!GELF_R_SYM(rela.r_info))
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continue; // symboil reference has been cleared in Case 1 above
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rela.relocBase = relocBase;
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uint8_t *relocand = ((uint8_t*) data->d_buf + rela.r_offset - shdr.sh_addr);
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if(relocBase == RelocBase::jumptable)
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{
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uint32_t dst = 0x20 + sym.jtIndex * 8 + 2;
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relocand[0] = dst >> 24;
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relocand[1] = dst >> 16;
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relocand[2] = dst >> 8;
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relocand[3] = dst;
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}
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else
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{
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uint32_t orig = (relocand[0] << 24) | (relocand[1] << 16) | (relocand[2] << 8) | relocand[3];
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uint32_t dst = orig + sym.section->outputBase - sym.section->shdr.sh_addr;
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relocand[0] = dst >> 24;
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relocand[1] = dst >> 16;
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relocand[2] = dst >> 8;
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relocand[3] = dst;
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}
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}
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}
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