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Alexander Shaposhnikov
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[llvm-objcopy][MachO] Handle relocation entries where r_extern is zero
Fix handling of relocations with r_extern == 0. If r_extern == 0 then r_symbolnum is an index of a section rather than a symbol index. Patch by Seiya Nuta and Alexander Shaposhnikov. Test plan: make check-all Differential revision: https://reviews.llvm.org/D78946
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+130
-12
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5 files changed

+130
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lines changed

‎llvm/test/tools/llvm-objcopy/MachO/relocations.test

Lines changed: 95 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,95 @@
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# RUN: yaml2obj %s -o %t
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## Show that llvm-objcopy copies relocation entries where r_extern = 0.
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# RUN: llvm-objcopy %t %t2
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# RUN: cmp %t %t2
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## Show that llvm-objcopy updates section indices properly.
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# RUN: llvm-objcopy --remove-section=__DATA,__foo %t %t3
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# RUN: llvm-objdump --macho --reloc %t3 | FileCheck %s
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# CHECK: Relocation information (__DATA,__bar) 2 entries
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# CHECK-NEXT: address pcrel length extern type scattered symbolnum/value
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# CHECK-NEXT: 00000000 False quad False SUB False 2 (__DATA,__bar)
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# CHECK-NEXT: 00000000 False quad False UNSIGND False 1 (__TEXT,__text)
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--- !mach-o
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FileHeader:
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magic: 0xFEEDFACF
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cputype: 0x01000007
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cpusubtype: 0x00000003
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filetype: 0x00000001
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ncmds: 1
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sizeofcmds: 312
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flags: 0x00000000
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reserved: 0x00000000
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LoadCommands:
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- cmd: LC_SEGMENT_64
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cmdsize: 312
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segname: ''
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vmaddr: 0
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vmsize: 24
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fileoff: 344
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filesize: 24
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maxprot: 7
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initprot: 7
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nsects: 3
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flags: 0
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Sections:
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- sectname: __text
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segname: __TEXT
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addr: 0x0000000000000000
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size: 8
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offset: 0x00000158
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align: 0
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reloff: 0x00000000
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nreloc: 0
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flags: 0x80000000
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reserved1: 0x00000000
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reserved2: 0x00000000
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reserved3: 0x00000000
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content: '0000000000000000'
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- sectname: __foo
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segname: __DATA
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addr: 0x0000000000000008
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size: 8
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offset: 0x00000160
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align: 0
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reloff: 0x00000000
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nreloc: 0
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flags: 0x00000000
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reserved1: 0x00000000
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reserved2: 0x00000000
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reserved3: 0x00000000
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content: '0000000000000000'
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- sectname: __bar
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segname: __DATA
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addr: 0x0000000000000010
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size: 8
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offset: 0x00000168
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align: 0
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reloff: 0x00000170
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nreloc: 2
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flags: 0x00000000
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reserved1: 0x00000000
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reserved2: 0x00000000
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reserved3: 0x00000000
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content: F0FFFFFFFFFFFFFF
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relocations:
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- address: 0x00000000
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symbolnum: 3
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pcrel: false
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length: 3
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extern: false
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type: 5
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scattered: false
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value: 0
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- address: 0x00000000
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symbolnum: 1
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pcrel: false
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length: 3
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extern: false
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type: 0
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scattered: false
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value: 0
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...

‎llvm/tools/llvm-objcopy/MachO/MachOReader.cpp

Lines changed: 19 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -103,6 +103,7 @@ extractSections(const object::MachOObjectFile::LoadCommandInfo &LoadCmd,
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R.Symbol = nullptr; // We'll fill this field later.
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R.Info = MachOObj.getRelocation(RI->getRawDataRefImpl());
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R.Scattered = MachOObj.isRelocationScattered(R.Info);
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R.Extern = !R.Scattered && MachOObj.getPlainRelocationExternal(R.Info);
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S.Relocations.push_back(R);
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}
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@@ -203,12 +204,27 @@ void MachOReader::readSymbolTable(Object &O) const {
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}
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void MachOReader::setSymbolInRelocationInfo(Object &O) const {
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std::vector<const Section *> Sections;
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for (auto &LC : O.LoadCommands)
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for (std::unique_ptr<Section> &Sec : LC.Sections)
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Sections.push_back(Sec.get());
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206212
for (LoadCommand &LC : O.LoadCommands)
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for (std::unique_ptr<Section> &Sec : LC.Sections)
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for (auto &Reloc : Sec->Relocations)
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if (!Reloc.Scattered)
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Reloc.Symbol = O.SymTable.getSymbolByIndex(
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Reloc.getPlainRelocationSymbolNum(MachOObj.isLittleEndian()));
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if (!Reloc.Scattered) {
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const uint32_t SymbolNum =
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Reloc.getPlainRelocationSymbolNum(MachOObj.isLittleEndian());
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if (Reloc.Extern) {
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Reloc.Symbol = O.SymTable.getSymbolByIndex(SymbolNum);
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} else {
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// FIXME: Refactor error handling in MachOReader and report an error
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// if we encounter an invalid relocation.
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assert(SymbolNum >= 1 && SymbolNum <= Sections.size() &&
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"Invalid section index.");
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Reloc.Section = Sections[SymbolNum - 1];
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}
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}
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}
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214230
void MachOReader::readRebaseInfo(Object &O) const {

‎llvm/tools/llvm-objcopy/MachO/MachOWriter.cpp

Lines changed: 7 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -239,11 +239,13 @@ void MachOWriter::writeSections() {
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memcpy(B.getBufferStart() + Sec->Offset, Sec->Content.data(),
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Sec->Content.size());
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for (size_t Index = 0; Index < Sec->Relocations.size(); ++Index) {
242-
auto RelocInfo = Sec->Relocations[Index];
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if (!RelocInfo.Scattered)
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RelocInfo.setPlainRelocationSymbolNum(RelocInfo.Symbol->Index,
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IsLittleEndian);
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RelocationInfo RelocInfo = Sec->Relocations[Index];
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if (!RelocInfo.Scattered) {
244+
const uint32_t SymbolNum = RelocInfo.Extern
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? (*RelocInfo.Symbol)->Index
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: (*RelocInfo.Section)->Index;
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RelocInfo.setPlainRelocationSymbolNum(SymbolNum, IsLittleEndian);
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}
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if (IsLittleEndian != sys::IsLittleEndianHost)
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MachO::swapStruct(
249251
reinterpret_cast<MachO::any_relocation_info &>(RelocInfo.Info));

‎llvm/tools/llvm-objcopy/MachO/Object.cpp

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -60,13 +60,13 @@ Error Object::removeSections(
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for (const LoadCommand &LC : LoadCommands)
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for (const std::unique_ptr<Section> &Sec : LC.Sections)
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for (const RelocationInfo &R : Sec->Relocations)
63-
if (R.Symbol && DeadSymbols.count(R.Symbol))
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if (R.Symbol && *R.Symbol && DeadSymbols.count(*R.Symbol))
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return createStringError(std::errc::invalid_argument,
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"symbol '%s' defined in section with index "
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"'%u' cannot be removed because it is "
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"referenced by a relocation in section '%s'",
68-
R.Symbol->Name.c_str(),
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*(R.Symbol->section()),
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(*R.Symbol)->Name.c_str(),
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*((*R.Symbol)->section()),
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Sec->CanonicalName.c_str());
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SymTable.removeSymbols(IsDead);
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for (std::unique_ptr<SymbolEntry> &S : SymTable.Symbols)

‎llvm/tools/llvm-objcopy/MachO/Object.h

Lines changed: 6 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -162,9 +162,14 @@ struct StringTable {
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};
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164164
struct RelocationInfo {
165-
const SymbolEntry *Symbol;
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// The referenced symbol entry. Set if !Scattered && Extern.
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Optional<const SymbolEntry *> Symbol;
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// The referenced section. Set if !Scattered && !Extern.
168+
Optional<const Section *> Section;
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// True if Info is a scattered_relocation_info.
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bool Scattered;
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// True if the r_symbolnum points to a section number (i.e. r_extern=0).
172+
bool Extern;
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MachO::any_relocation_info Info;
169174

170175
unsigned getPlainRelocationSymbolNum(bool IsLittleEndian) {

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