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CodeGen: support an extension to pass linker options on ELF 

Introduce an extension to support passing linker options to the linker.
These would be ignored by older linkers, but newer linkers which support
this feature would be able to process the linker.

Emit a special discarded section `.linker-option`.  The content of this
section is a pair of strings (key, value).  The key is a type identifier for
the parameter.  This allows for an argument free parameter that will be
processed by the linker with the value being the parameter.  As an example,
`lib` identifies a library to be linked against, traditionally the `-l`
argument for Unix-based linkers with the parameter being the library name.

Thanks to James Henderson, Cary Coutant, Rafael Espinolda, Sean Silva
for the valuable discussion on the design of this feature.

llvm-svn: 323783
This commit is contained in:
Saleem Abdulrasool 2018-01-30 16:29:29 +00:00
parent f1d01645a7
commit b36fbbc3ec
13 changed files with 185 additions and 37 deletions
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38
llvm/docs/Extensions.rst
View File

@ -221,6 +221,44 @@ which is equivalent to just
.section .foo,"a",@progbits
.section .bar,"ao",@progbits,.foo
``.linker-options`` Section (linker options)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
In order to support passing linker options from the frontend to the linker, a
special section of type ``SHT_LLVM_LINKER_OPTIONS`` (usually named
``.linker-options`` though the name is not significant as it is identified by
the type). The contents of this section is a simple pair-wise encoding of
options for consideration by the linker. The strings are encoded as standard
null-terminated UTF-8 strings. They are emitted inline to avoid having the
linker to traverse the object file for retrieving the value. The linker is
permitted to not honour the option and instead provide a warning/error to the
user that the requested option was not honoured.
The section is marked as ``SHT_LLVM_LINKER_OPTIONS`` and has the ``SHF_EXCLUDE``
flag to ensure that the section is treated as opaque by linkers which do not
support the feature and will not be emitted into the final linked binary.
This would be equivalent to the follow raw assembly:
.. code-block:: gas
.section ".linker-options","e",@llvm_linker_options
.asciz "option 1"
.asciz "value 1"
.asciz "option 2"
.asciz "value 2"
LLVM emits the following options:
- lib
The parameter identifies a library to be linked against. The library will
be looked up in the default and any specified library search paths
(specified to this point).
- path
The paramter identifies an additional library search path to be considered
when looking up libraries after the inclusion of this option.
Target Specific Behaviour
=========================

73
llvm/include/llvm/BinaryFormat/ELF.h
View File

@ -714,36 +714,37 @@ enum {
// Section types.
enum : unsigned {
SHT_NULL = 0, // No associated section (inactive entry).
SHT_PROGBITS = 1, // Program-defined contents.
SHT_SYMTAB = 2, // Symbol table.
SHT_STRTAB = 3, // String table.
SHT_RELA = 4, // Relocation entries; explicit addends.
SHT_HASH = 5, // Symbol hash table.
SHT_DYNAMIC = 6, // Information for dynamic linking.
SHT_NOTE = 7, // Information about the file.
SHT_NOBITS = 8, // Data occupies no space in the file.
SHT_REL = 9, // Relocation entries; no explicit addends.
SHT_SHLIB = 10, // Reserved.
SHT_DYNSYM = 11, // Symbol table.
SHT_INIT_ARRAY = 14, // Pointers to initialization functions.
SHT_FINI_ARRAY = 15, // Pointers to termination functions.
SHT_PREINIT_ARRAY = 16, // Pointers to pre-init functions.
SHT_GROUP = 17, // Section group.
SHT_SYMTAB_SHNDX = 18, // Indices for SHN_XINDEX entries.
SHT_LOOS = 0x60000000, // Lowest operating system-specific type.
SHT_NULL = 0, // No associated section (inactive entry).
SHT_PROGBITS = 1, // Program-defined contents.
SHT_SYMTAB = 2, // Symbol table.
SHT_STRTAB = 3, // String table.
SHT_RELA = 4, // Relocation entries; explicit addends.
SHT_HASH = 5, // Symbol hash table.
SHT_DYNAMIC = 6, // Information for dynamic linking.
SHT_NOTE = 7, // Information about the file.
SHT_NOBITS = 8, // Data occupies no space in the file.
SHT_REL = 9, // Relocation entries; no explicit addends.
SHT_SHLIB = 10, // Reserved.
SHT_DYNSYM = 11, // Symbol table.
SHT_INIT_ARRAY = 14, // Pointers to initialization functions.
SHT_FINI_ARRAY = 15, // Pointers to termination functions.
SHT_PREINIT_ARRAY = 16, // Pointers to pre-init functions.
SHT_GROUP = 17, // Section group.
SHT_SYMTAB_SHNDX = 18, // Indices for SHN_XINDEX entries.
SHT_LOOS = 0x60000000, // Lowest operating system-specific type.
// Android packed relocation section types.
// https://android.googlesource.com/platform/bionic/+/6f12bfece5dcc01325e0abba56a46b1bcf991c69/tools/relocation_packer/src/elf_file.cc#37
SHT_ANDROID_REL = 0x60000001,
SHT_ANDROID_RELA = 0x60000002,
SHT_LLVM_ODRTAB = 0x6fff4c00, // LLVM ODR table.
SHT_GNU_ATTRIBUTES = 0x6ffffff5, // Object attributes.
SHT_GNU_HASH = 0x6ffffff6, // GNU-style hash table.
SHT_GNU_verdef = 0x6ffffffd, // GNU version definitions.
SHT_GNU_verneed = 0x6ffffffe, // GNU version references.
SHT_GNU_versym = 0x6fffffff, // GNU symbol versions table.
SHT_HIOS = 0x6fffffff, // Highest operating system-specific type.
SHT_LOPROC = 0x70000000, // Lowest processor arch-specific type.
SHT_LLVM_ODRTAB = 0x6fff4c00, // LLVM ODR table.
SHT_LLVM_LINKER_OPTIONS = 0x6fff4c01, // LLVM Linker Options.
SHT_GNU_ATTRIBUTES = 0x6ffffff5, // Object attributes.
SHT_GNU_HASH = 0x6ffffff6, // GNU-style hash table.
SHT_GNU_verdef = 0x6ffffffd, // GNU version definitions.
SHT_GNU_verneed = 0x6ffffffe, // GNU version references.
SHT_GNU_versym = 0x6fffffff, // GNU symbol versions table.
SHT_HIOS = 0x6fffffff, // Highest operating system-specific type.
SHT_LOPROC = 0x70000000, // Lowest processor arch-specific type.
// Fixme: All this is duplicated in MCSectionELF. Why??
// Exception Index table
SHT_ARM_EXIDX = 0x70000001U,
@ -753,18 +754,18 @@ enum : unsigned {
SHT_ARM_ATTRIBUTES = 0x70000003U,
SHT_ARM_DEBUGOVERLAY = 0x70000004U,
SHT_ARM_OVERLAYSECTION = 0x70000005U,
SHT_HEX_ORDERED = 0x70000000, // Link editor is to sort the entries in
// this section based on their sizes
SHT_X86_64_UNWIND = 0x70000001, // Unwind information
SHT_HEX_ORDERED = 0x70000000, // Link editor is to sort the entries in
// this section based on their sizes
SHT_X86_64_UNWIND = 0x70000001, // Unwind information
SHT_MIPS_REGINFO = 0x70000006, // Register usage information
SHT_MIPS_OPTIONS = 0x7000000d, // General options
SHT_MIPS_DWARF = 0x7000001e, // DWARF debugging section.
SHT_MIPS_ABIFLAGS = 0x7000002a, // ABI information.
SHT_MIPS_REGINFO = 0x70000006, // Register usage information
SHT_MIPS_OPTIONS = 0x7000000d, // General options
SHT_MIPS_DWARF = 0x7000001e, // DWARF debugging section.
SHT_MIPS_ABIFLAGS = 0x7000002a, // ABI information.
SHT_HIPROC = 0x7fffffff, // Highest processor arch-specific type.
SHT_LOUSER = 0x80000000, // Lowest type reserved for applications.
SHT_HIUSER = 0xffffffff // Highest type reserved for applications.
SHT_HIPROC = 0x7fffffff, // Highest processor arch-specific type.
SHT_LOUSER = 0x80000000, // Lowest type reserved for applications.
SHT_HIUSER = 0xffffffff // Highest type reserved for applications.
};
// Section flags.

19
llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
View File

@ -93,6 +93,24 @@ static void GetObjCImageInfo(Module &M, unsigned &Version, unsigned &Flags,
void TargetLoweringObjectFileELF::emitModuleMetadata(
MCStreamer &Streamer, Module &M, const TargetMachine &TM) const {
auto &C = getContext();
if (NamedMDNode *LinkerOptions = M.getNamedMetadata("llvm.linker.options")) {
auto *S = C.getELFSection(".linker-options", ELF::SHT_LLVM_LINKER_OPTIONS,
ELF::SHF_EXCLUDE);
Streamer.SwitchSection(S);
for (const auto &Operand : LinkerOptions->operands()) {
if (cast<MDNode>(Operand)->getNumOperands() != 2)
report_fatal_error("invalid llvm.linker.options");
for (const auto &Option : cast<MDNode>(Operand)->operands()) {
Streamer.EmitBytes(cast<MDString>(Option)->getString());
Streamer.EmitIntValue(0, 1);
}
}
}
unsigned Version = 0;
unsigned Flags = 0;
StringRef Section;
@ -101,7 +119,6 @@ void TargetLoweringObjectFileELF::emitModuleMetadata(
if (Section.empty())
return;
auto &C = getContext();
auto *S = C.getELFSection(Section, ELF::SHT_PROGBITS, ELF::SHF_ALLOC);
Streamer.SwitchSection(S);
Streamer.EmitLabel(C.getOrCreateSymbol(StringRef("OBJC_IMAGE_INFO")));

2
llvm/lib/MC/MCParser/ELFAsmParser.cpp
View File

@ -608,6 +608,8 @@ EndStmt:
Type = ELF::SHT_X86_64_UNWIND;
else if (TypeName == "llvm_odrtab")
Type = ELF::SHT_LLVM_ODRTAB;
else if (TypeName == "llvm_linker_options")
Type = ELF::SHT_LLVM_LINKER_OPTIONS;
else if (TypeName.getAsInteger(0, Type))
return TokError("unknown section type");
}

2
llvm/lib/MC/MCSectionELF.cpp
View File

@ -148,6 +148,8 @@ void MCSectionELF::PrintSwitchToSection(const MCAsmInfo &MAI, const Triple &T,
OS << "0x7000001e";
else if (Type == ELF::SHT_LLVM_ODRTAB)
OS << "llvm_odrtab";
else if (Type == ELF::SHT_LLVM_LINKER_OPTIONS)
OS << "llvm_linker_options";
else
report_fatal_error("unsupported type 0x" + Twine::utohexstr(Type) +
" for section " + getSectionName());

1
llvm/lib/Object/ELF.cpp
View File

@ -205,6 +205,7 @@ StringRef llvm::object::getELFSectionTypeName(uint32_t Machine, unsigned Type) {
STRINGIFY_ENUM_CASE(ELF, SHT_ANDROID_REL);
STRINGIFY_ENUM_CASE(ELF, SHT_ANDROID_RELA);
STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_ODRTAB);
STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_LINKER_OPTIONS);
STRINGIFY_ENUM_CASE(ELF, SHT_GNU_ATTRIBUTES);
STRINGIFY_ENUM_CASE(ELF, SHT_GNU_HASH);
STRINGIFY_ENUM_CASE(ELF, SHT_GNU_verdef);

1
llvm/lib/ObjectYAML/ELFYAML.cpp
View File

@ -408,6 +408,7 @@ void ScalarEnumerationTraits<ELFYAML::ELF_SHT>::enumeration(
ECase(SHT_ANDROID_REL);
ECase(SHT_ANDROID_RELA);
ECase(SHT_LLVM_ODRTAB);
ECase(SHT_LLVM_LINKER_OPTIONS);
ECase(SHT_GNU_ATTRIBUTES);
ECase(SHT_GNU_HASH);
ECase(SHT_GNU_verdef);

16
llvm/test/Feature/elf-linker-options.ll Normal file
View File

@ -0,0 +1,16 @@
; RUN: llc -mtriple x86_64-elf -filetype asm -o - %s | FileCheck %s
!llvm.linker.options = !{!0, !1}
!0 = !{!"option 0", !"value 0"}
!1 = !{!"option 1", !"value 1"}
; CHECK: .section ".linker-options","e",@llvm_linker_options
; CHECK-NEXT: .ascii "option 0"
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "value 0"
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "option 1"
; CHECK-NEXT: .byte 0
; CHECK-NEXT: .ascii "value 1"
; CHECK-NEXT: .byte 0

14
llvm/test/MC/ELF/section.s
View File

@ -279,3 +279,17 @@ bar:
// CHECK-NEXT: Flags [
// CHECK-NEXT: SHF_EXCLUDE
// CHECK-NEXT: ]
// Test SHT_LLVM_LINKER_OPTIONS
.section ".linker-options","e",@llvm_linker_options
// ASM: .section ".linker-options","e",@llvm_linker_options
// CHECK: Section {
// CHECK: Name: .linker-options
// CHECK-NEXT: Type: SHT_LLVM_LINKER_OPTIONS
// CHECK-NEXT: Flags [
// CHECK-NEXT: SHF_EXCLUDE
// CHECK-NEXT: ]
// CHECK: }

11
llvm/test/tools/llvm-readobj/elf-linker-options.ll Normal file
View File

@ -0,0 +1,11 @@
; RUN: llc -mtriple x86_64-elf -filetype obj -o - %s | llvm-readobj -elf-linker-options - | FileCheck %s
!llvm.linker.options = !{!0, !1}
!0 = !{!"option 0", !"value 0"}
!1 = !{!"option 1", !"value 1"}
; CHECK: LinkerOptions [
; CHECK: option 0: value 0
; CHECK: option 1: value 1
; CHECK: ]

37
llvm/tools/llvm-readobj/ELFDumper.cpp
View File

@ -164,6 +164,8 @@ public:
void printNotes() override;
void printELFLinkerOptions() override;
private:
std::unique_ptr<DumpStyle<ELFT>> ELFDumperStyle;
@ -316,6 +318,7 @@ public:
virtual void printProgramHeaders(const ELFFile<ELFT> *Obj) = 0;
virtual void printHashHistogram(const ELFFile<ELFT> *Obj) = 0;
virtual void printNotes(const ELFFile<ELFT> *Obj) = 0;
virtual void printELFLinkerOptions(const ELFFile<ELFT> *Obj) = 0;
virtual void printMipsGOT(const MipsGOTParser<ELFT> &Parser) = 0;
virtual void printMipsPLT(const MipsGOTParser<ELFT> &Parser) = 0;
const ELFDumper<ELFT> *dumper() const { return Dumper; }
@ -345,6 +348,7 @@ public:
void printProgramHeaders(const ELFO *Obj) override;
void printHashHistogram(const ELFFile<ELFT> *Obj) override;
void printNotes(const ELFFile<ELFT> *Obj) override;
void printELFLinkerOptions(const ELFFile<ELFT> *Obj) override;
void printMipsGOT(const MipsGOTParser<ELFT> &Parser) override;
void printMipsPLT(const MipsGOTParser<ELFT> &Parser) override;
@ -405,6 +409,7 @@ public:
void printProgramHeaders(const ELFO *Obj) override;
void printHashHistogram(const ELFFile<ELFT> *Obj) override;
void printNotes(const ELFFile<ELFT> *Obj) override;
void printELFLinkerOptions(const ELFFile<ELFT> *Obj) override;
void printMipsGOT(const MipsGOTParser<ELFT> &Parser) override;
void printMipsPLT(const MipsGOTParser<ELFT> &Parser) override;
@ -1501,6 +1506,10 @@ template <class ELFT> void ELFDumper<ELFT>::printNotes() {
ELFDumperStyle->printNotes(Obj);
}
template <class ELFT> void ELFDumper<ELFT>::printELFLinkerOptions() {
ELFDumperStyle->printELFLinkerOptions(Obj);
}
#define LLVM_READOBJ_TYPE_CASE(name) \
case DT_##name: return #name
@ -2694,6 +2703,8 @@ std::string getSectionTypeString(unsigned Arch, unsigned Type) {
return "SYMTAB SECTION INDICES";
case SHT_LLVM_ODRTAB:
return "LLVM_ODRTAB";
case SHT_LLVM_LINKER_OPTIONS:
return "LLVM_LINKER_OPTIONS";
// FIXME: Parse processor specific GNU attributes
case SHT_GNU_ATTRIBUTES:
return "ATTRIBUTES";
@ -3554,6 +3565,11 @@ void GNUStyle<ELFT>::printNotes(const ELFFile<ELFT> *Obj) {
}
}
template <class ELFT>
void GNUStyle<ELFT>::printELFLinkerOptions(const ELFFile<ELFT> *Obj) {
OS << "printELFLinkerOptions not implemented!\n";
}
template <class ELFT>
void GNUStyle<ELFT>::printMipsGOT(const MipsGOTParser<ELFT> &Parser) {
size_t Bias = ELFT::Is64Bits ? 8 : 0;
@ -4062,6 +4078,27 @@ void LLVMStyle<ELFT>::printNotes(const ELFFile<ELFT> *Obj) {
W.startLine() << "printNotes not implemented!\n";
}
template <class ELFT>
void LLVMStyle<ELFT>::printELFLinkerOptions(const ELFFile<ELFT> *Obj) {
ListScope L(W, "LinkerOptions");
for (const Elf_Shdr &Shdr : unwrapOrError(Obj->sections())) {
if (Shdr.sh_type != ELF::SHT_LLVM_LINKER_OPTIONS)
continue;
ArrayRef<uint8_t> Contents = unwrapOrError(Obj->getSectionContents(&Shdr));
for (const uint8_t *P = Contents.begin(), *E = Contents.end(); P < E; ) {
StringRef Key = StringRef(reinterpret_cast<const char *>(P));
StringRef Value =
StringRef(reinterpret_cast<const char *>(P) + Key.size() + 1);
W.printString(Key, Value);
P = P + Key.size() + Value.size() + 2;
}
}
}
template <class ELFT>
void LLVMStyle<ELFT>::printMipsGOT(const MipsGOTParser<ELFT> &Parser) {
auto PrintEntry = [&](const Elf_Addr *E) {

1
llvm/tools/llvm-readobj/ObjDumper.h
View File

@ -48,6 +48,7 @@ public:
virtual void printGroupSections() {}
virtual void printHashHistogram() {}
virtual void printNotes() {}
virtual void printELFLinkerOptions() {}
// Only implemented for ARM ELF at this time.
virtual void printAttributes() { }

7
llvm/tools/llvm-readobj/llvm-readobj.cpp
View File

@ -229,6 +229,11 @@ namespace opts {
COFFLoadConfig("coff-load-config",
cl::desc("Display the PE/COFF load config"));
// -elf-linker-options
cl::opt<bool>
ELFLinkerOptions("elf-linker-options",
cl::desc("Display the ELF .linker-options section"));
// -macho-data-in-code
cl::opt<bool>
MachODataInCode("macho-data-in-code",
@ -419,6 +424,8 @@ static void dumpObject(const ObjectFile *Obj, ScopedPrinter &Writer) {
if (opts::VersionInfo)
Dumper->printVersionInfo();
if (Obj->isELF()) {
if (opts::ELFLinkerOptions)
Dumper->printELFLinkerOptions();
if (Obj->getArch() == llvm::Triple::arm)
if (opts::ARMAttributes)
Dumper->printAttributes();