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[llvm-objcopy] Implement support for section groups 

This diff adds support for SHT_GROUP sections to llvm-objcopy.
Some sections are interrelated and comprise a group.
For example, a definition of an inline function might require, 
in addition to the section containing its instructions, 
a read-only data section containing literals referenced inside the function.
A section of the type SHT_GROUP contains the indices of the group members,
therefore, it needs to be updated whenever the indices change.
Similarly, the fields sh_link, sh_info should be recalculated as well.

Test plan: make check-all

Differential revision: https://reviews.llvm.org/D43996

llvm-svn: 328012
This commit is contained in:
Alexander Shaposhnikov 2018-03-20 18:20:42 +00:00
parent a3f2e483dd
commit 43b8acdfd7
6 changed files with 272 additions and 43 deletions
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BIN
llvm/test/tools/llvm-objcopy/Inputs/groups.o Normal file
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56
llvm/test/tools/llvm-objcopy/group-unchanged.test Normal file
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@ -0,0 +1,56 @@
# RUN: yaml2obj %s > %t
# RUN: llvm-objcopy -remove-section=.text.bar %t %t2
# RUN: llvm-readobj -elf-section-groups %t2 | FileCheck %s
# In this test the section .text.bar is getting removed, since this section
# goes after all the sections comprising a group, the content of the
# section .group doesn't change.
# CHECK: Name: .group
# CHECK-NEXT: Index: 1
# CHECK-NEXT: Link: 3
# CHECK-NEXT: Info: 2
# CHECK-NEXT: Type: COMDAT (0x1)
# CHECK-NEXT: Signature: foo
# CHECK: .text.foo (2)
--- !ELF
FileHeader:
Class: ELFCLASS64
Data: ELFDATA2LSB
Type: ET_REL
Machine: EM_X86_64
Sections:
- Name: .group
Type: SHT_GROUP
Link: .symtab
AddressAlign: 0x0000000000000004
Info: foo
Members:
- SectionOrType: GRP_COMDAT
- SectionOrType: .text.foo
- Name: .text.foo
Type: SHT_PROGBITS
Flags: [ SHF_ALLOC, SHF_EXECINSTR, SHF_GROUP ]
AddressAlign: 0x0000000000000010
- Name: .text.bar
Type: SHT_PROGBITS
Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
AddressAlign: 0x0000000000000010
Symbols:
Local:
- Name: .text.foo
Type: STT_SECTION
Section: .text.foo
- Name: .text.bar
Type: STT_SECTION
Section: .text.bar
Weak:
- Name: foo
Type: STT_FUNC
Section: .text.foo
Size: 0x0000000000000000
- Name: bar
Type: STT_FUNC
Section: .text.bar
Size: 0x0000000000000000

56
llvm/test/tools/llvm-objcopy/group.test Normal file
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@ -0,0 +1,56 @@
# RUN: yaml2obj %s > %t
# RUN: llvm-objcopy -remove-section=.text.bar %t %t2
# RUN: llvm-readobj -elf-section-groups %t2 | FileCheck %s
# In this test the section .text.bar is getting removed, as a result,
# the indices of the sections which go after .text.bar will change,
# thus the fields Link, Info and the content of .group should be updated.
# CHECK: Name: .group
# CHECK-NEXT: Index: 1
# CHECK-NEXT: Link: 3
# CHECK-NEXT: Info: 2
# CHECK-NEXT: Type: COMDAT (0x1)
# CHECK-NEXT: Signature: foo
# CHECK: .text.foo (2)
--- !ELF
FileHeader:
Class: ELFCLASS64
Data: ELFDATA2LSB
Type: ET_REL
Machine: EM_X86_64
Sections:
- Name: .group
Type: SHT_GROUP
Link: .symtab
AddressAlign: 0x0000000000000004
Info: foo
Members:
- SectionOrType: GRP_COMDAT
- SectionOrType: .text.foo
- Name: .text.bar
Type: SHT_PROGBITS
Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
AddressAlign: 0x0000000000000010
- Name: .text.foo
Type: SHT_PROGBITS
Flags: [ SHF_ALLOC, SHF_EXECINSTR, SHF_GROUP ]
AddressAlign: 0x0000000000000010
Symbols:
Local:
- Name: .text.bar
Type: STT_SECTION
Section: .text.bar
- Name: .text.foo
Type: STT_SECTION
Section: .text.foo
Weak:
- Name: bar
Type: STT_FUNC
Section: .text.bar
Size: 0x0000000000000000
- Name: foo
Type: STT_FUNC
Section: .text.foo
Size: 0x0000000000000000

40
llvm/test/tools/llvm-objcopy/strip-dwo-groups.test Normal file
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@ -0,0 +1,40 @@
# RUN: cp %p/Inputs/groups.o %t
# RUN: llvm-objcopy -strip-dwo %t
# RUN: llvm-readobj -elf-section-groups %t | FileCheck %s
// Source code of groups.o:
//
// template <class T>
// struct S {
// static constexpr T X = T(1);
// T getX() { return X; }
// };
// void f() {
// S<int> A;
// S<double> B;
// int a = A.getX();
// int b = B.getX();
// }
//
// clang -g -gsplit-dwarf -std=c++11 -c groups.cpp -o groups.o
// `llvm-objcopy -strip-dwo` strips out dwo sections, as a result, the index of
// the symbol table, the indices of the symbols and the indices of the sections
// which go after the removed ones will change. Consequently, the fields
// Link, Info and the content of .group need to be updated. In the past
// `llvm-objcopy -strip-dwo` used to produce invalid binaries with
// broken .group section, this test verifies the correctness of
// Link, Info and the content of this section.
CHECK: Name: .group (179)
CHECK-NEXT: Index: 17
CHECK-NEXT: Link: 19
CHECK-NEXT: Info: 14
CHECK: .text._ZN1SIiE4getXEv (2)
CHECK: Name: .group (179)
CHECK-NEXT: Index: 18
CHECK-NEXT: Link: 19
CHECK-NEXT: Info: 13
CHECK: .text._ZN1SIdE4getXEv (4)
CHECK-NEXT: .rela.text._ZN1SIdE4getXEv (21)

98
llvm/tools/llvm-objcopy/Object.cpp
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@ -77,7 +77,11 @@ void BinarySectionWriter::visit(const RelocationSection &Sec) {
}
void BinarySectionWriter::visit(const GnuDebugLinkSection &Sec) {
error("Cannot write '.gnu_debuglink' out to binary");
error("Cannot write '" + Sec.Name + "' out to binary");
}
void BinarySectionWriter::visit(const GroupSection &Sec) {
error("Cannot write '" + Sec.Name + "' out to binary");
}
void SectionWriter::visit(const Section &Sec) {
@ -155,6 +159,12 @@ uint16_t Symbol::getShndx() const {
llvm_unreachable("Symbol with invalid ShndxType encountered");
}
void SymbolTableSection::assignIndices() {
uint32_t Index = 0;
for (auto &Sym : Symbols)
Sym->Index = Index++;
}
void SymbolTableSection::addSymbol(StringRef Name, uint8_t Bind, uint8_t Type,
SectionBase *DefinedIn, uint64_t Value,
uint8_t Visibility, uint16_t Shndx,
@ -189,6 +199,7 @@ void SymbolTableSection::removeSectionReferences(const SectionBase *Sec) {
[=](const SymPtr &Sym) { return Sym->DefinedIn == Sec; });
Size -= (std::end(Symbols) - Iter) * this->EntrySize;
Symbols.erase(Iter, std::end(Symbols));
assignIndices();
}
void SymbolTableSection::localize(
@ -203,11 +214,7 @@ void SymbolTableSection::localize(
std::stable_partition(
std::begin(Symbols), std::end(Symbols),
[](const SymPtr &Sym) { return Sym->Binding == STB_LOCAL; });
// Lastly we fix the symbol indexes.
uint32_t Index = 0;
for (auto &Sym : Symbols)
Sym->Index = Index++;
assignIndices();
}
void SymbolTableSection::initialize(SectionTableRef SecTable) {
@ -274,9 +281,10 @@ template <class SymTabType>
void RelocSectionWithSymtabBase<SymTabType>::removeSectionReferences(
const SectionBase *Sec) {
if (Symbols == Sec) {
error("Symbol table " + Symbols->Name + " cannot be removed because it is "
"referenced by the relocation "
"section " +
error("Symbol table " + Symbols->Name +
" cannot be removed because it is "
"referenced by the relocation "
"section " +
this->Name);
}
}
@ -291,9 +299,9 @@ void RelocSectionWithSymtabBase<SymTabType>::initialize(
" is not a symbol table"));
if (Info != SHN_UNDEF)
setSection(SecTable.getSection(Info,
"Info field value " + Twine(Info) +
" in section " + Name + " is invalid"));
setSection(SecTable.getSection(Info, "Info field value " + Twine(Info) +
" in section " + Name +
" is invalid"));
else
setSection(nullptr);
}
@ -347,20 +355,49 @@ void DynamicRelocationSection::accept(SectionVisitor &Visitor) const {
void SectionWithStrTab::removeSectionReferences(const SectionBase *Sec) {
if (StrTab == Sec) {
error("String table " + StrTab->Name + " cannot be removed because it is "
"referenced by the section " +
error("String table " + StrTab->Name +
" cannot be removed because it is "
"referenced by the section " +
this->Name);
}
}
void GroupSection::initialize(SectionTableRef SecTable) {
SymTab = SecTable.getSectionOfType<SymbolTableSection>(
Link,
"Link field value " + Twine(Link) + " in section " + Name + " is invalid",
"Link field value " + Twine(Link) + " in section " + Name +
" is not a symbol table");
Sym = SymTab->getSymbolByIndex(Info);
if (!Sym)
error("Info field value " + Twine(Info) + " in section " + Name +
" is not a valid symbol index");
if (Contents.size() % sizeof(ELF::Elf32_Word) || Contents.empty())
error("The content of the section " + Name + " is malformed");
const ELF::Elf32_Word *Word =
reinterpret_cast<const ELF::Elf32_Word *>(Contents.data());
const ELF::Elf32_Word *End = Word + Contents.size() / sizeof(ELF::Elf32_Word);
FlagWord = *Word++;
for (; Word != End; ++Word) {
GroupMembers.push_back(
SecTable.getSection(*Word, "Group member index " + Twine(*Word) +
" in section " + Name + " is invalid"));
}
}
void GroupSection::finalize() {
this->Info = Sym->Index;
this->Link = SymTab->Index;
}
bool SectionWithStrTab::classof(const SectionBase *S) {
return isa<DynamicSymbolTableSection>(S) || isa<DynamicSection>(S);
}
void SectionWithStrTab::initialize(SectionTableRef SecTable) {
auto StrTab = SecTable.getSection(Link,
"Link field value " + Twine(Link) +
" in section " + Name + " is invalid");
auto StrTab =
SecTable.getSection(Link, "Link field value " + Twine(Link) +
" in section " + Name + " is invalid");
if (StrTab->Type != SHT_STRTAB) {
error("Link field value " + Twine(Link) + " in section " + Name +
" is not a string table");
@ -416,6 +453,19 @@ void GnuDebugLinkSection::accept(SectionVisitor &Visitor) const {
Visitor.visit(*this);
}
template <class ELFT>
void ELFSectionWriter<ELFT>::visit(const GroupSection &Sec) {
ELF::Elf32_Word *Buf =
reinterpret_cast<ELF::Elf32_Word *>(Out.getBufferStart() + Sec.Offset);
*Buf++ = Sec.FlagWord;
for (const auto *S : Sec.GroupMembers)
*Buf++ = S->Index;
}
void GroupSection::accept(SectionVisitor &Visitor) const {
Visitor.visit(*this);
}
// Returns true IFF a section is wholly inside the range of a segment
static bool sectionWithinSegment(const SectionBase &Section,
const Segment &Segment) {
@ -455,8 +505,7 @@ static bool compareSegmentsByPAddr(const Segment *A, const Segment *B) {
return A->Index < B->Index;
}
template <class ELFT>
void ELFBuilder<ELFT>::setParentSegment(Segment &Child) {
template <class ELFT> void ELFBuilder<ELFT>::setParentSegment(Segment &Child) {
for (auto &Parent : Obj.segments()) {
// Every segment will overlap with itself but we don't want a segment to
// be it's own parent so we avoid that situation.
@ -522,7 +571,7 @@ template <class ELFT> void ELFBuilder<ELFT>::readProgramHeaders() {
PrHdr.OriginalOffset = PrHdr.Offset = PrHdr.VAddr = Ehdr.e_phoff;
PrHdr.PAddr = 0;
PrHdr.FileSize = PrHdr.MemSize = Ehdr.e_phentsize * Ehdr.e_phnum;
// The spec requires us to naturally align all the fields.
// The spec requires us to naturally align all the fields.
PrHdr.Align = sizeof(Elf_Addr);
PrHdr.Index = Index++;
@ -552,9 +601,9 @@ void ELFBuilder<ELFT>::initSymbolTable(SymbolTableSection *SymTab) {
}
} else if (Sym.st_shndx != SHN_UNDEF) {
DefSection = Obj.sections().getSection(
Sym.st_shndx,
"Symbol '" + Name + "' is defined in invalid section with index " +
Twine(Sym.st_shndx));
Sym.st_shndx, "Symbol '" + Name +
"' is defined in invalid section with index " +
Twine(Sym.st_shndx));
}
SymTab->addSymbol(Name, Sym.getBinding(), Sym.getType(), DefSection,
@ -623,6 +672,9 @@ SectionBase &ELFBuilder<ELFT>::makeSection(const Elf_Shdr &Shdr) {
// Because of this we don't need to mess with the hash tables either.
Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
return Obj.addSection<Section>(Data);
case SHT_GROUP:
Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
return Obj.addSection<GroupSection>(Data);
case SHT_DYNSYM:
Data = unwrapOrError(ElfFile.getSectionContents(&Shdr));
return Obj.addSection<DynamicSymbolTableSection>(Data);

65
llvm/tools/llvm-objcopy/Object.h
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@ -35,17 +35,17 @@ class SymbolTableSection;
class RelocationSection;
class DynamicRelocationSection;
class GnuDebugLinkSection;
class GroupSection;
class Segment;
class Object;
class SectionTableRef {
private:
MutableArrayRef<std::unique_ptr<SectionBase>> Sections;
public:
using iterator = pointee_iterator<std::unique_ptr<SectionBase> *>;
SectionTableRef(MutableArrayRef<std::unique_ptr<SectionBase>> Secs)
explicit SectionTableRef(MutableArrayRef<std::unique_ptr<SectionBase>> Secs)
: Sections(Secs) {}
SectionTableRef(const SectionTableRef &) = default;
@ -71,6 +71,7 @@ public:
virtual void visit(const RelocationSection &Sec) = 0;
virtual void visit(const DynamicRelocationSection &Sec) = 0;
virtual void visit(const GnuDebugLinkSection &Sec) = 0;
virtual void visit(const GroupSection &Sec) = 0;
};
class SectionWriter : public SectionVisitor {
@ -87,6 +88,7 @@ public:
virtual void visit(const SymbolTableSection &Sec) override = 0;
virtual void visit(const RelocationSection &Sec) override = 0;
virtual void visit(const GnuDebugLinkSection &Sec) override = 0;
virtual void visit(const GroupSection &Sec) override = 0;
SectionWriter(FileOutputBuffer &Buf) : Out(Buf) {}
};
@ -102,6 +104,7 @@ public:
void visit(const SymbolTableSection &Sec) override;
void visit(const RelocationSection &Sec) override;
void visit(const GnuDebugLinkSection &Sec) override;
void visit(const GroupSection &Sec) override;
ELFSectionWriter(FileOutputBuffer &Buf) : SectionWriter(Buf) {}
};
@ -117,6 +120,8 @@ public:
void visit(const SymbolTableSection &Sec) override;
void visit(const RelocationSection &Sec) override;
void visit(const GnuDebugLinkSection &Sec) override;
void visit(const GroupSection &Sec) override;
BinarySectionWriter(FileOutputBuffer &Buf) : SectionWriter(Buf) {}
};
@ -237,7 +242,7 @@ public:
uint64_t OriginalOffset;
Segment *ParentSegment = nullptr;
Segment(ArrayRef<uint8_t> Data) : Contents(Data) {}
explicit Segment(ArrayRef<uint8_t> Data) : Contents(Data) {}
Segment() {}
const SectionBase *firstSection() const {
@ -253,11 +258,10 @@ public:
class Section : public SectionBase {
MAKE_SEC_WRITER_FRIEND
private:
ArrayRef<uint8_t> Contents;
public:
Section(ArrayRef<uint8_t> Data) : Contents(Data) {}
explicit Section(ArrayRef<uint8_t> Data) : Contents(Data) {}
void accept(SectionVisitor &Visitor) const override;
};
@ -265,7 +269,6 @@ public:
class OwnedDataSection : public SectionBase {
MAKE_SEC_WRITER_FRIEND
private:
std::vector<uint8_t> Data;
public:
@ -291,7 +294,6 @@ public:
class StringTableSection : public SectionBase {
MAKE_SEC_WRITER_FRIEND
private:
StringTableBuilder StrTabBuilder;
public:
@ -344,6 +346,7 @@ class SymbolTableSection : public SectionBase {
MAKE_SEC_WRITER_FRIEND
void setStrTab(StringTableSection *StrTab) { SymbolNames = StrTab; }
void assignIndices();
protected:
std::vector<std::unique_ptr<Symbol>> Symbols;
@ -402,7 +405,6 @@ public:
// that code between the two symbol table types.
template <class SymTabType>
class RelocSectionWithSymtabBase : public RelocationSectionBase {
private:
SymTabType *Symbols = nullptr;
void setSymTab(SymTabType *SymTab) { Symbols = SymTab; }
@ -419,7 +421,6 @@ class RelocationSection
: public RelocSectionWithSymtabBase<SymbolTableSection> {
MAKE_SEC_WRITER_FRIEND
private:
std::vector<Relocation> Relocations;
public:
@ -433,14 +434,37 @@ public:
}
};
class SectionWithStrTab : public Section {
private:
const SectionBase *StrTab = nullptr;
// TODO: The way stripping and groups interact is complicated
// and still needs to be worked on.
class GroupSection : public SectionBase {
MAKE_SEC_WRITER_FRIEND
// TODO: Contents is present in several classes of the hierarchy.
// This needs to be refactored to avoid duplication.
ArrayRef<uint8_t> Contents;
ELF::Elf32_Word FlagWord;
SmallVector<SectionBase *, 3> GroupMembers;
const SymbolTableSection *SymTab = nullptr;
const Symbol *Sym = nullptr;
public:
SectionWithStrTab(ArrayRef<uint8_t> Data) : Section(Data) {}
explicit GroupSection(ArrayRef<uint8_t> Data) : Contents(Data) {}
void initialize(SectionTableRef SecTable) override;
void accept(SectionVisitor &) const override;
void finalize() override;
static bool classof(const SectionBase *S) {
return S->Type == ELF::SHT_GROUP;
}
};
class SectionWithStrTab : public Section {
const SectionBase *StrTab = nullptr;
void setStrTab(const SectionBase *StringTable) { StrTab = StringTable; }
public:
explicit SectionWithStrTab(ArrayRef<uint8_t> Data) : Section(Data) {}
void removeSectionReferences(const SectionBase *Sec) override;
void initialize(SectionTableRef SecTable) override;
void finalize() override;
@ -449,7 +473,8 @@ public:
class DynamicSymbolTableSection : public SectionWithStrTab {
public:
DynamicSymbolTableSection(ArrayRef<uint8_t> Data) : SectionWithStrTab(Data) {}
explicit DynamicSymbolTableSection(ArrayRef<uint8_t> Data)
: SectionWithStrTab(Data) {}
static bool classof(const SectionBase *S) {
return S->Type == ELF::SHT_DYNSYM;
@ -458,7 +483,7 @@ public:
class DynamicSection : public SectionWithStrTab {
public:
DynamicSection(ArrayRef<uint8_t> Data) : SectionWithStrTab(Data) {}
explicit DynamicSection(ArrayRef<uint8_t> Data) : SectionWithStrTab(Data) {}
static bool classof(const SectionBase *S) {
return S->Type == ELF::SHT_DYNAMIC;
@ -473,7 +498,7 @@ private:
ArrayRef<uint8_t> Contents;
public:
DynamicRelocationSection(ArrayRef<uint8_t> Data) : Contents(Data) {}
explicit DynamicRelocationSection(ArrayRef<uint8_t> Data) : Contents(Data) {}
void accept(SectionVisitor &) const override;
@ -488,7 +513,6 @@ class GnuDebugLinkSection : public SectionBase {
MAKE_SEC_WRITER_FRIEND
private:
StringRef FileName;
uint32_t CRC32;
@ -496,7 +520,7 @@ private:
public:
// If we add this section from an external source we can use this ctor.
GnuDebugLinkSection(StringRef File);
explicit GnuDebugLinkSection(StringRef File);
void accept(SectionVisitor &Visitor) const override;
};
@ -506,10 +530,10 @@ public:
virtual std::unique_ptr<Object> create() const = 0;
};
using object::OwningBinary;
using object::Binary;
using object::ELFFile;
using object::ELFObjectFile;
using object::OwningBinary;
template <class ELFT> class ELFBuilder {
private:
@ -582,7 +606,8 @@ public:
StringTableSection *SectionNames = nullptr;
SymbolTableSection *SymbolTable = nullptr;
Object(std::shared_ptr<MemoryBuffer> Data) : OwnedData(Data) {}
explicit Object(std::shared_ptr<MemoryBuffer> Data)
: OwnedData(std::move(Data)) {}
virtual ~Object() = default;
void sortSections();