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[yaml2obj] - Change how we handle implicit sections. 

We have a few sections that can be added implicitly to the output:
".dynsym", ".dynstr", ".symtab", ".strtab" and ".shstrtab".

Problem appears when such section is listed explicitly in YAML.
In that case it's content is written twice:
first time during writing of regular sections listed in the document
and second time during special handling.

Because of that their file offsets can become unexpectedly broken:
(yaml file for sample below lists .dynsym explicitly before .text.foo)

Before patch:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .dynsym           DYNSYM           0000000000000100  00000250
       0000000000000030  0000000000000018   A       6     0     8
  [ 2] .text.foo         PROGBITS         0000000000000200  00000200
       0000000000000000  0000000000000000  AX       0     0     0

After patch:
Section Headers:
  [Nr] Name         Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .dynsym           DYNSYM           0000000000000100  00000200
       0000000000000030  0000000000000018   A       6     0     8
  [ 2] .text.foo         PROGBITS         0000000000000200  00000230
       0000000000000000  0000000000000000  AX       0     0     0

This patch reorganizes our code and fixes the issue described.

Differential revision: https://reviews.llvm.org/D62809

llvm-svn: 362602
This commit is contained in:
George Rimar 2019-06-05 13:16:53 +00:00
parent f95e6c0653
commit 66296dc3e4
2 changed files with 206 additions and 63 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

86
llvm/test/tools/yaml2obj/implicit-sections.test Normal file
View File

@ -0,0 +1,86 @@
## Check the section header properties of ".dynsym",
## ".dynstr", ".symtab", ".strtab", ".shstrtab".
## These sections sections are usually added implicitly,
## but here we add them explicitly in YAML and verify.
## We check their order matches YAML and that file offset is
## ascending. This is a natural default behavior.
# RUN: yaml2obj --docnum=1 %s -o %t1
# RUN: llvm-readelf -S %t1 | FileCheck %s
# CHECK: Section Headers:
# CHECK-NEXT: [Nr] Name Type Address Off Size
# CHECK-NEXT: [ 0] NULL 0000000000000000 000000 000000
# CHECK-NEXT: [ 1] .dynstr STRTAB 0000000000000100 000200 000009
# CHECK-NEXT: [ 2] .dynsym DYNSYM 0000000000000150 000209 000030
# CHECK-NEXT: [ 3] .symtab SYMTAB 0000000000000000 000239 000018
# CHECK-NEXT: [ 4] .strtab STRTAB 0000000000000000 000251 000001
# CHECK-NEXT: [ 5] .shstrtab STRTAB 0000000000000000 000252 000035
# CHECK-NEXT: [ 6] .text.foo PROGBITS 0000000000000200 000287 000000
--- !ELF
FileHeader:
Class: ELFCLASS64
Data: ELFDATA2LSB
Type: ET_DYN
Machine: EM_X86_64
Sections:
- Name: .dynstr
Type: SHT_STRTAB
Address: 0x100
- Name: .dynsym
Type: SHT_DYNSYM
Address: 0x150
- Name: .symtab
Type: SHT_SYMTAB
- Name: .strtab
Type: SHT_STRTAB
- Name: .shstrtab
Type: SHT_STRTAB
- Name: .text.foo
Type: SHT_PROGBITS
Address: 0x200
## Symbol is required for the .dynsym to be generated.
DynamicSymbols:
- Name: _Z3fooi
Binding: STB_GLOBAL
## Check that yaml2obj creates empty .dynstr and .dynsym sections for
## the case when no dynamic symbols were specified and Content wasn't set,
## but the sections were explicitly listed. Check their VAs are correct.
# RUN: yaml2obj --docnum=2 %s -o %t2
# RUN: llvm-readelf -S %t2 | FileCheck %s --check-prefix=NODYNSYM
# NODYNSYM: Section Headers:
# NODYNSYM-NEXT: [Nr] Name Type Address Off Size
# NODYNSYM-NEXT: [ 0] NULL 0000000000000000 000000 000000
# NODYNSYM-NEXT: [ 1] .dynstr STRTAB 0000000000000100 000200 000001
# NODYNSYM-NEXT: [ 2] .dynsym DYNSYM 0000000000000150 000201 000018
# NODYNSYM-NEXT: [ 3] .symtab SYMTAB 0000000000000000 000219 000018
# NODYNSYM-NEXT: [ 4] .strtab STRTAB 0000000000000000 000231 000001
# NODYNSYM-NEXT: [ 5] .shstrtab STRTAB 0000000000000000 000232 000035
# NODYNSYM-NEXT: [ 6] .text.foo PROGBITS 0000000000000200 000267 000000
--- !ELF
FileHeader:
Class: ELFCLASS64
Data: ELFDATA2LSB
Type: ET_DYN
Machine: EM_X86_64
Sections:
- Name: .dynstr
Type: SHT_STRTAB
Address: 0x100
- Name: .dynsym
Type: SHT_DYNSYM
Address: 0x150
- Name: .symtab
Type: SHT_SYMTAB
- Name: .strtab
Type: SHT_STRTAB
- Name: .shstrtab
Type: SHT_STRTAB
- Name: .text.foo
Type: SHT_PROGBITS
Address: 0x200

183
llvm/tools/yaml2obj/yaml2elf.cpp
View File

@ -136,13 +136,19 @@ class ELFState {
bool buildSymbolIndex(ArrayRef<ELFYAML::Symbol> Symbols);
void initELFHeader(Elf_Ehdr &Header);
void initProgramHeaders(std::vector<Elf_Phdr> &PHeaders);
bool initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
bool initImplicitHeader(ELFState<ELFT> &State, ContiguousBlobAccumulator &CBA,
Elf_Shdr &Header, StringRef SecName,
ELFYAML::Section *YAMLSec);
bool initSectionHeaders(ELFState<ELFT> &State,
std::vector<Elf_Shdr> &SHeaders,
ContiguousBlobAccumulator &CBA);
void initSymtabSectionHeader(Elf_Shdr &SHeader, SymtabType STType,
ContiguousBlobAccumulator &CBA);
ContiguousBlobAccumulator &CBA,
ELFYAML::Section *YAMLSec);
void initStrtabSectionHeader(Elf_Shdr &SHeader, StringRef Name,
StringTableBuilder &STB,
ContiguousBlobAccumulator &CBA);
ContiguousBlobAccumulator &CBA,
ELFYAML::Section *YAMLSec);
void setProgramHeaderLayout(std::vector<Elf_Phdr> &PHeaders,
std::vector<Elf_Shdr> &SHeaders);
void addSymbols(ArrayRef<ELFYAML::Symbol> Symbols, std::vector<Elf_Sym> &Syms,
@ -248,7 +254,36 @@ static bool convertSectionIndex(NameToIdxMap &SN2I, StringRef SecName,
}
template <class ELFT>
bool ELFState<ELFT>::initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
bool ELFState<ELFT>::initImplicitHeader(ELFState<ELFT> &State,
ContiguousBlobAccumulator &CBA,
Elf_Shdr &Header, StringRef SecName,
ELFYAML::Section *YAMLSec) {
// Check if the header was already initialized.
if (Header.sh_offset)
return false;
if (SecName == ".symtab")
State.initSymtabSectionHeader(Header, SymtabType::Static, CBA, YAMLSec);
else if (SecName == ".strtab")
State.initStrtabSectionHeader(Header, SecName, State.DotStrtab, CBA,
YAMLSec);
else if (SecName == ".shstrtab")
State.initStrtabSectionHeader(Header, SecName, State.DotShStrtab, CBA,
YAMLSec);
else if (SecName == ".dynsym")
State.initSymtabSectionHeader(Header, SymtabType::Dynamic, CBA, YAMLSec);
else if (SecName == ".dynstr")
State.initStrtabSectionHeader(Header, SecName, State.DotDynstr, CBA,
YAMLSec);
else
return false;
return true;
}
template <class ELFT>
bool ELFState<ELFT>::initSectionHeaders(ELFState<ELFT> &State,
std::vector<Elf_Shdr> &SHeaders,
ContiguousBlobAccumulator &CBA) {
// Ensure SHN_UNDEF entry is present. An all-zero section header is a
// valid SHN_UNDEF entry since SHT_NULL == 0.
@ -271,6 +306,15 @@ bool ELFState<ELFT>::initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
SHeader.sh_link = Index;
}
// We have a few sections like string or symbol tables that are added
// implicitly later. However, if they are explicitly specified in the YAML,
// we want to write them right now. This ensures the file offset remains
// correct.
if (initImplicitHeader(State, CBA, SHeader, Sec->Name, Sec.get())) {
SHeaders.push_back(SHeader);
continue;
}
if (auto S = dyn_cast<ELFYAML::RawContentSection>(Sec.get())) {
if (!writeSectionContent(SHeader, *S, CBA))
return false;
@ -306,6 +350,26 @@ bool ELFState<ELFT>::initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
SHeaders.push_back(SHeader);
}
// Populate SHeaders with implicit sections not present in the Doc.
for (StringRef Name : State.implicitSectionNames())
if (State.SN2I.get(Name) >= SHeaders.size())
SHeaders.push_back({});
// Initialize the implicit sections.
initImplicitHeader(State, CBA, SHeaders[State.SN2I.get(".symtab")], ".symtab",
nullptr /*DocSec*/);
initImplicitHeader(State, CBA, SHeaders[State.SN2I.get(".strtab")], ".strtab",
nullptr /*DocSec*/);
initImplicitHeader(State, CBA, SHeaders[State.SN2I.get(".shstrtab")],
".shstrtab", nullptr /*DocSec*/);
if (!Doc.DynamicSymbols.empty()) {
initImplicitHeader(State, CBA, SHeaders[State.SN2I.get(".dynsym")],
".dynsym", nullptr /*DocSec*/);
initImplicitHeader(State, CBA, SHeaders[State.SN2I.get(".dynstr")],
".dynstr", nullptr /*DocSec*/);
}
return true;
}
@ -319,7 +383,8 @@ static size_t findFirstNonGlobal(ArrayRef<ELFYAML::Symbol> Symbols) {
template <class ELFT>
void ELFState<ELFT>::initSymtabSectionHeader(Elf_Shdr &SHeader,
SymtabType STType,
ContiguousBlobAccumulator &CBA) {
ContiguousBlobAccumulator &CBA,
ELFYAML::Section *YAMLSec) {
zero(SHeader);
bool IsStatic = STType == SymtabType::Static;
SHeader.sh_name = DotShStrtab.getOffset(IsStatic ? ".symtab" : ".dynsym");
@ -330,57 +395,71 @@ void ELFState<ELFT>::initSymtabSectionHeader(Elf_Shdr &SHeader,
// One greater than symbol table index of the last local symbol.
const auto &Symbols = IsStatic ? Doc.Symbols : Doc.DynamicSymbols;
SHeader.sh_info = findFirstNonGlobal(Symbols) + 1;
SHeader.sh_entsize = sizeof(Elf_Sym);
SHeader.sh_addralign = 8;
// Get the section index ignoring the SHT_NULL section.
unsigned SecNdx =
IsStatic ? getDotSymTabSecNo() - 1 : getDotDynSymSecNo() - 1;
// If the symbol table section is explicitly described in the YAML
// then we should set the fields requested.
if (SecNdx < Doc.Sections.size()) {
ELFYAML::Section *Sec = Doc.Sections[SecNdx].get();
SHeader.sh_addr = Sec->Address;
if (auto S = dyn_cast<ELFYAML::RawContentSection>(Sec))
SHeader.sh_info = S->Info;
ELFYAML::RawContentSection *RawSec =
dyn_cast_or_null<ELFYAML::RawContentSection>(YAMLSec);
SHeader.sh_info =
RawSec ? (unsigned)RawSec->Info : findFirstNonGlobal(Symbols) + 1;
SHeader.sh_entsize = (YAMLSec && YAMLSec->EntSize)
? (uint64_t)(*YAMLSec->EntSize)
: sizeof(Elf_Sym);
SHeader.sh_addralign = YAMLSec ? (uint64_t)YAMLSec->AddressAlign : 8;
SHeader.sh_addr = YAMLSec ? (uint64_t)YAMLSec->Address : 0;
if (RawSec && RawSec->Content.binary_size()) {
RawSec->Content.writeAsBinary(
CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign));
SHeader.sh_size = RawSec->Size;
} else {
std::vector<Elf_Sym> Syms;
{
// Ensure STN_UNDEF is present
Elf_Sym Sym;
zero(Sym);
Syms.push_back(Sym);
}
addSymbols(Symbols, Syms, IsStatic ? DotStrtab : DotDynstr);
writeArrayData(
CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign),
makeArrayRef(Syms));
SHeader.sh_size = arrayDataSize(makeArrayRef(Syms));
}
std::vector<Elf_Sym> Syms;
{
// Ensure STN_UNDEF is present
Elf_Sym Sym;
zero(Sym);
Syms.push_back(Sym);
}
addSymbols(Symbols, Syms, IsStatic ? DotStrtab : DotDynstr);
writeArrayData(
CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign),
makeArrayRef(Syms));
SHeader.sh_size = arrayDataSize(makeArrayRef(Syms));
}
template <class ELFT>
void ELFState<ELFT>::initStrtabSectionHeader(Elf_Shdr &SHeader, StringRef Name,
StringTableBuilder &STB,
ContiguousBlobAccumulator &CBA) {
ContiguousBlobAccumulator &CBA,
ELFYAML::Section *YAMLSec) {
zero(SHeader);
SHeader.sh_name = DotShStrtab.getOffset(Name);
SHeader.sh_type = ELF::SHT_STRTAB;
STB.write(CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign));
SHeader.sh_size = STB.getSize();
SHeader.sh_addralign = 1;
SHeader.sh_addralign = YAMLSec ? (uint64_t)YAMLSec->AddressAlign : 1;
ELFYAML::RawContentSection *RawSec =
dyn_cast_or_null<ELFYAML::RawContentSection>(YAMLSec);
if (RawSec && RawSec->Content.binary_size()) {
RawSec->Content.writeAsBinary(
CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign));
SHeader.sh_size = RawSec->Size;
} else {
STB.write(
CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign));
SHeader.sh_size = STB.getSize();
}
if (YAMLSec && YAMLSec->EntSize)
SHeader.sh_entsize = *YAMLSec->EntSize;
// If .dynstr section is explicitly described in the YAML
// then we want to use its section address.
if (Name == ".dynstr") {
// Take section index and ignore the SHT_NULL section.
unsigned SecNdx = getDotDynStrSecNo() - 1;
if (SecNdx < Doc.Sections.size())
SHeader.sh_addr = Doc.Sections[SecNdx]->Address;
if (YAMLSec)
SHeader.sh_addr = YAMLSec->Address;
// We assume that .dynstr is always allocatable.
SHeader.sh_flags |= ELF::SHF_ALLOC;
}
@ -841,9 +920,6 @@ template <class ELFT> void ELFState<ELFT>::finalizeStrings() {
DotStrtab.add(Sym.Name);
DotStrtab.finalize();
if (Doc.DynamicSymbols.empty())
return;
// Add the dynamic symbol names to .dynstr section.
for (const ELFYAML::Symbol &Sym : Doc.DynamicSymbols)
DotDynstr.add(Sym.Name);
@ -898,28 +974,9 @@ int ELFState<ELFT>::writeELF(raw_ostream &OS, const ELFYAML::Object &Doc) {
ContiguousBlobAccumulator CBA(SectionContentBeginOffset);
std::vector<Elf_Shdr> SHeaders;
if (!State.initSectionHeaders(SHeaders, CBA))
if (!State.initSectionHeaders(State, SHeaders, CBA))
return 1;
// Populate SHeaders with implicit sections not present in the Doc
for (StringRef Name : State.implicitSectionNames())
if (State.SN2I.get(Name) >= SHeaders.size())
SHeaders.push_back({});
// Initialize the implicit sections
State.initSymtabSectionHeader(SHeaders[State.SN2I.get(".symtab")],
SymtabType::Static, CBA);
State.initStrtabSectionHeader(SHeaders[State.SN2I.get(".strtab")], ".strtab",
State.DotStrtab, CBA);
State.initStrtabSectionHeader(SHeaders[State.SN2I.get(".shstrtab")],
".shstrtab", State.DotShStrtab, CBA);
if (!Doc.DynamicSymbols.empty()) {
State.initSymtabSectionHeader(SHeaders[State.SN2I.get(".dynsym")],
SymtabType::Dynamic, CBA);
State.initStrtabSectionHeader(SHeaders[State.SN2I.get(".dynstr")],
".dynstr", State.DotDynstr, CBA);
}
// Now we can decide segment offsets
State.setProgramHeaderLayout(PHeaders, SHeaders);