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MC: Implement support for new .addrsig and .addrsig_sym directives.

Browse Source 
Part of the address-significance tables proposal:
http://lists.llvm.org/pipermail/llvm-dev/2018-May/123514.html

Differential Revision: https://reviews.llvm.org/D47744

llvm-svn: 337328
This commit is contained in:
Peter Collingbourne 2018-07-17 22:17:18 +00:00
parent b27e787f6c
commit ec56d20419
16 changed files with 278 additions and 0 deletions
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30
docs/Extensions.rst
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@ -329,6 +329,36 @@ symbol is undefined, then that symbol is defined as if ``.weak symbol`` has been
written at the end of the file. This forces the symbol to show up in the symbol
table.
``SHT_LLVM_ADDRSIG`` Section (address-significance table)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This section is used to mark symbols as address-significant, i.e. the address
of the symbol is used in a comparison or leaks outside the translation unit. It
has the same meaning as the absence of the LLVM attributes ``unnamed_addr``
and ``local_unnamed_addr``.
Any sections referred to by symbols that are not marked as address-significant
in any object file may be safely merged by a linker without breaking the
address uniqueness guarantee provided by the C and C++ language standards.
The contents of the section are a sequence of ULEB128-encoded integers
referring to the symbol table indexes of the address-significant symbols.
There are two associated assembly directives:
.. code-block:: gas
.addrsig
This instructs the assembler to emit an address-significance table. Without
this directive, all symbols are considered address-significant.
.. code-block:: gas
.addrsig_sym sym
This marks ``sym`` as address-significant.
CodeView-Dependent
------------------

2
include/llvm/BinaryFormat/ELF.h
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@ -797,6 +797,8 @@ enum : unsigned {
SHT_LLVM_ODRTAB = 0x6fff4c00, // LLVM ODR table.
SHT_LLVM_LINKER_OPTIONS = 0x6fff4c01, // LLVM Linker Options.
SHT_LLVM_CALL_GRAPH_PROFILE = 0x6fff4c02, // LLVM Call Graph Profile.
SHT_LLVM_ADDRSIG = 0x6fff4c03, // List of address-significant symbols
// for safe ICF.
// Android's experimental support for SHT_RELR sections.
// https://android.googlesource.com/platform/bionic/+/b7feec74547f84559a1467aca02708ff61346d2a/libc/include/elf.h#512
SHT_ANDROID_RELR = 0x6fffff00, // Relocation entries; only offsets.

3
include/llvm/MC/MCObjectStreamer.h
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@ -170,6 +170,9 @@ public:
SMLoc Loc = SMLoc()) override;
void EmitFileDirective(StringRef Filename) override;
void EmitAddrsig() override;
void EmitAddrsigSym(const MCSymbol *Sym) override;
void FinishImpl() override;
/// Emit the absolute difference between two symbols if possible.

9
include/llvm/MC/MCObjectWriter.h
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@ -92,6 +92,15 @@ public:
bool InSet,
bool IsPCRel) const;
/// Tell the object writer to emit an address-significance table during
/// writeObject(). If this function is not called, all symbols are treated as
/// address-significant.
virtual void emitAddrsigSection() {}
/// Record the given symbol in the address-significance table to be written
/// diring writeObject().
virtual void addAddrsigSymbol(const MCSymbol *Sym) {}
/// Write the object file and returns the number of bytes written.
///
/// This routine is called by the assembler after layout and relaxation is

3
include/llvm/MC/MCStreamer.h
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@ -924,6 +924,9 @@ public:
return true;
}
virtual void EmitAddrsig() {}
virtual void EmitAddrsigSym(const MCSymbol *Sym) {}
/// Emit the given \p Instruction into the current section.
/// PrintSchedInfo == true then schedul comment should be added to output
virtual void EmitInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,

37
lib/MC/ELFObjectWriter.cpp
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@ -43,6 +43,7 @@
#include "llvm/Support/Error.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/Host.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/SMLoc.h"
#include "llvm/Support/StringSaver.h"
@ -199,6 +200,8 @@ public:
const RevGroupMapTy &RevGroupMap,
SectionOffsetsTy &SectionOffsets);
void writeAddrsigSection();
MCSectionELF *createRelocationSection(MCContext &Ctx,
const MCSectionELF &Sec);
@ -232,6 +235,9 @@ class ELFObjectWriter : public MCObjectWriter {
DenseMap<const MCSymbolELF *, const MCSymbolELF *> Renames;
bool EmitAddrsigSection = false;
std::vector<const MCSymbol *> AddrsigSyms;
bool hasRelocationAddend() const;
bool shouldRelocateWithSymbol(const MCAssembler &Asm,
@ -267,6 +273,11 @@ public:
void executePostLayoutBinding(MCAssembler &Asm,
const MCAsmLayout &Layout) override;
void emitAddrsigSection() override { EmitAddrsigSection = true; }
void addAddrsigSymbol(const MCSymbol *Sym) override {
AddrsigSyms.push_back(Sym);
}
friend struct ELFWriter;
};
@ -747,6 +758,11 @@ void ELFWriter::computeSymbolTable(
SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
}
void ELFWriter::writeAddrsigSection() {
for (const MCSymbol *Sym : OWriter.AddrsigSyms)
encodeULEB128(Sym->getIndex(), W.OS);
}
MCSectionELF *ELFWriter::createRelocationSection(MCContext &Ctx,
const MCSectionELF &Sec) {
if (OWriter.Relocations[&Sec].empty())
@ -977,6 +993,7 @@ void ELFWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
case ELF::SHT_SYMTAB_SHNDX:
case ELF::SHT_LLVM_CALL_GRAPH_PROFILE:
case ELF::SHT_LLVM_ADDRSIG:
sh_link = SymbolTableIndex;
break;
@ -1123,6 +1140,13 @@ uint64_t ELFWriter::writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) {
// string tables.
StrTabBuilder.finalize();
} else {
MCSectionELF *AddrsigSection;
if (OWriter.EmitAddrsigSection) {
AddrsigSection = Ctx.getELFSection(".llvm_addrsig", ELF::SHT_LLVM_ADDRSIG,
ELF::SHF_EXCLUDE);
addToSectionTable(AddrsigSection);
}
// Compute symbol table information.
computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
SectionOffsets);
@ -1139,6 +1163,13 @@ uint64_t ELFWriter::writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) {
uint64_t SecEnd = W.OS.tell();
SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
}
if (OWriter.EmitAddrsigSection) {
uint64_t SecStart = W.OS.tell();
writeAddrsigSection();
uint64_t SecEnd = W.OS.tell();
SectionOffsets[AddrsigSection] = std::make_pair(SecStart, SecEnd);
}
}
if (CGProfileSection) {
@ -1238,6 +1269,12 @@ void ELFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
Renames.insert(std::make_pair(&Symbol, Alias));
}
for (const MCSymbol *&Sym : AddrsigSyms) {
if (const MCSymbol *R = Renames.lookup(cast<MCSymbolELF>(Sym)))
Sym = R;
Sym->setUsedInReloc();
}
}
// It is always valid to create a relocation with a symbol. It is preferable

14
lib/MC/MCAsmStreamer.cpp
View File

@ -319,6 +319,9 @@ public:
const MCExpr *Expr, SMLoc Loc,
const MCSubtargetInfo &STI) override;
void EmitAddrsig() override;
void EmitAddrsigSym(const MCSymbol *Sym) override;
/// If this file is backed by an assembly streamer, this dumps the specified
/// string in the output .s file. This capability is indicated by the
/// hasRawTextSupport() predicate.
@ -1846,6 +1849,17 @@ bool MCAsmStreamer::EmitRelocDirective(const MCExpr &Offset, StringRef Name,
return false;
}
void MCAsmStreamer::EmitAddrsig() {
OS << "\t.addrsig";
EmitEOL();
}
void MCAsmStreamer::EmitAddrsigSym(const MCSymbol *Sym) {
OS << "\t.addrsig_sym ";
Sym->print(OS, MAI);
EmitEOL();
}
/// EmitRawText - If this file is backed by an assembly streamer, this dumps
/// the specified string in the output .s file. This capability is
/// indicated by the hasRawTextSupport() predicate.

9
lib/MC/MCObjectStreamer.cpp
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@ -660,6 +660,15 @@ void MCObjectStreamer::EmitFileDirective(StringRef Filename) {
getAssembler().addFileName(Filename);
}
void MCObjectStreamer::EmitAddrsig() {
getAssembler().getWriter().emitAddrsigSection();
}
void MCObjectStreamer::EmitAddrsigSym(const MCSymbol *Sym) {
getAssembler().registerSymbol(*Sym);
getAssembler().getWriter().addAddrsigSymbol(Sym);
}
void MCObjectStreamer::FinishImpl() {
getContext().RemapDebugPaths();

27
lib/MC/MCParser/AsmParser.cpp
View File

@ -506,6 +506,8 @@ private:
DK_ERROR,
DK_WARNING,
DK_PRINT,
DK_ADDRSIG,
DK_ADDRSIG_SYM,
DK_END
};
@ -654,6 +656,10 @@ private:
// .print <double-quotes-string>
bool parseDirectivePrint(SMLoc DirectiveLoc);
// Directives to support address-significance tables.
bool parseDirectiveAddrsig();
bool parseDirectiveAddrsigSym();
void initializeDirectiveKindMap();
};
@ -2127,6 +2133,10 @@ bool AsmParser::parseStatement(ParseStatementInfo &Info,
return parseDirectiveDS(IDVal, 12);
case DK_PRINT:
return parseDirectivePrint(IDLoc);
case DK_ADDRSIG:
return parseDirectiveAddrsig();
case DK_ADDRSIG_SYM:
return parseDirectiveAddrsigSym();
}
return Error(IDLoc, "unknown directive");
@ -5291,6 +5301,8 @@ void AsmParser::initializeDirectiveKindMap() {
DirectiveKindMap[".ds.w"] = DK_DS_W;
DirectiveKindMap[".ds.x"] = DK_DS_X;
DirectiveKindMap[".print"] = DK_PRINT;
DirectiveKindMap[".addrsig"] = DK_ADDRSIG;
DirectiveKindMap[".addrsig_sym"] = DK_ADDRSIG_SYM;
}
MCAsmMacro *AsmParser::parseMacroLikeBody(SMLoc DirectiveLoc) {
@ -5530,6 +5542,21 @@ bool AsmParser::parseDirectivePrint(SMLoc DirectiveLoc) {
return false;
}
bool AsmParser::parseDirectiveAddrsig() {
getStreamer().EmitAddrsig();
return false;
}
bool AsmParser::parseDirectiveAddrsigSym() {
StringRef Name;
if (check(parseIdentifier(Name),
"expected identifier in '.addrsig_sym' directive"))
return true;
MCSymbol *Sym = getContext().getOrCreateSymbol(Name);
getStreamer().EmitAddrsigSym(Sym);
return false;
}
// We are comparing pointers, but the pointers are relative to a single string.
// Thus, this should always be deterministic.
static int rewritesSort(const AsmRewrite *AsmRewriteA,

1
lib/Object/ELF.cpp
View File

@ -246,6 +246,7 @@ StringRef llvm::object::getELFSectionTypeName(uint32_t Machine, unsigned Type) {
STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_ODRTAB);
STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_LINKER_OPTIONS);
STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_CALL_GRAPH_PROFILE);
STRINGIFY_ENUM_CASE(ELF, SHT_LLVM_ADDRSIG);
STRINGIFY_ENUM_CASE(ELF, SHT_GNU_ATTRIBUTES);
STRINGIFY_ENUM_CASE(ELF, SHT_GNU_HASH);
STRINGIFY_ENUM_CASE(ELF, SHT_GNU_verdef);

1
lib/ObjectYAML/ELFYAML.cpp
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@ -444,6 +444,7 @@ void ScalarEnumerationTraits<ELFYAML::ELF_SHT>::enumeration(
ECase(SHT_LLVM_ODRTAB);
ECase(SHT_LLVM_LINKER_OPTIONS);
ECase(SHT_LLVM_CALL_GRAPH_PROFILE);
ECase(SHT_LLVM_ADDRSIG);
ECase(SHT_GNU_ATTRIBUTES);
ECase(SHT_GNU_HASH);
ECase(SHT_GNU_verdef);

5
test/MC/ELF/addrsig-error.s Normal file
View File

@ -0,0 +1,5 @@
// RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - 2>&1 | FileCheck %s
// CHECK: Undefined temporary symbol
.addrsig
.addrsig_sym .Lundef

86
test/MC/ELF/addrsig.s Normal file
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@ -0,0 +1,86 @@
// RUN: llvm-mc -filetype=asm -triple x86_64-pc-linux-gnu %s -o - | FileCheck --check-prefix=ASM %s
// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-readobj -s -t -sd -elf-addrsig | FileCheck %s
// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -split-dwarf-file %t.dwo -o - | llvm-readobj -s -t -sd -elf-addrsig | FileCheck %s
// RUN: llvm-readobj -s %t.dwo | FileCheck --check-prefix=DWO %s
// CHECK: Name: .llvm_addrsig
// CHECK-NEXT: Type: SHT_LLVM_ADDRSIG (0x6FFF4C03)
// CHECK-NEXT: Flags [ (0x80000000)
// CHECK-NEXT: SHF_EXCLUDE (0x80000000)
// CHECK-NEXT: ]
// CHECK-NEXT: Address:
// CHECK-NEXT: Offset:
// CHECK-NEXT: Size: 4
// CHECK-NEXT: Link: 4
// CHECK-NEXT: Info: 0
// CHECK-NEXT: AddressAlignment: 1
// CHECK-NEXT: EntrySize: 0
// CHECK-NEXT: SectionData (
// CHECK-NEXT: 0000: 03050201
// CHECK-NEXT: )
// CHECK-NEXT: }
// CHECK-NEXT: Section {
// CHECK-NEXT: Index: 4
// CHECK-NEXT: Name: .symtab
// CHECK: Name: .Llocal
// CHECK-NEXT: Value:
// CHECK-NEXT: Size:
// CHECK-NEXT: Binding:
// CHECK-NEXT: Type:
// CHECK-NEXT: Other:
// CHECK-NEXT: Section:
// CHECK-NEXT: }
// CHECK-NEXT: Symbol {
// CHECK-NEXT: Name: local
// CHECK-NEXT: Value:
// CHECK-NEXT: Size:
// CHECK-NEXT: Binding:
// CHECK-NEXT: Type:
// CHECK-NEXT: Other:
// CHECK-NEXT: Section:
// CHECK-NEXT: }
// CHECK-NEXT: Symbol {
// CHECK-NEXT: Name: g1
// CHECK-NEXT: Value:
// CHECK-NEXT: Size:
// CHECK-NEXT: Binding:
// CHECK-NEXT: Type:
// CHECK-NEXT: Other:
// CHECK-NEXT: Section:
// CHECK-NEXT: }
// CHECK-NEXT: Symbol {
// CHECK-NEXT: Name: g2
// CHECK-NEXT: Value:
// CHECK-NEXT: Size:
// CHECK-NEXT: Binding:
// CHECK-NEXT: Type:
// CHECK-NEXT: Other:
// CHECK-NEXT: Section:
// CHECK-NEXT: }
// CHECK-NEXT: Symbol {
// CHECK-NEXT: Name: g3
// CHECK: Addrsig [
// CHECK-NEXT: Sym: g1 (3)
// CHECK-NEXT: Sym: g3 (5)
// CHECK-NEXT: Sym: local (2)
// CHECK-NEXT: Sym: .Llocal (1)
// CHECK-NEXT: ]
// ASM: .addrsig
.addrsig
// ASM: .addrsig_sym g1
.addrsig_sym g1
.globl g2
// ASM: .addrsig_sym g3
.addrsig_sym g3
// ASM: .addrsig_sym local
.addrsig_sym local
// ASM: .addrsig_sym .Llocal
.addrsig_sym .Llocal
local:
.Llocal:
// DWO-NOT: .llvm_addrsig

45
tools/llvm-readobj/ELFDumper.cpp
View File

@ -44,6 +44,7 @@
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/FormattedStream.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/MipsABIFlags.h"
#include "llvm/Support/ScopedPrinter.h"
@ -170,6 +171,7 @@ public:
void printHashHistogram() override;
void printCGProfile() override;
void printAddrsig() override;
void printNotes() override;
@ -219,6 +221,7 @@ private:
const Elf_GnuHash *GnuHashTable = nullptr;
const Elf_Shdr *DotSymtabSec = nullptr;
const Elf_Shdr *DotCGProfileSec = nullptr;
const Elf_Shdr *DotAddrsigSec = nullptr;
StringRef DynSymtabName;
ArrayRef<Elf_Word> ShndxTable;
@ -272,6 +275,7 @@ public:
void printSymbolsHelper(bool IsDynamic) const;
const Elf_Shdr *getDotSymtabSec() const { return DotSymtabSec; }
const Elf_Shdr *getDotCGProfileSec() const { return DotCGProfileSec; }
const Elf_Shdr *getDotAddrsigSec() const { return DotAddrsigSec; }
ArrayRef<Elf_Word> getShndxTable() const { return ShndxTable; }
StringRef getDynamicStringTable() const { return DynamicStringTable; }
const DynRegionInfo &getDynRelRegion() const { return DynRelRegion; }
@ -352,6 +356,7 @@ public:
StringRef SectionName) = 0;
virtual void printHashHistogram(const ELFFile<ELFT> *Obj) = 0;
virtual void printCGProfile(const ELFFile<ELFT> *Obj) = 0;
virtual void printAddrsig(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;
@ -384,6 +389,7 @@ public:
void printSectionAsString(const ELFO *Obj, StringRef SectionName) override;
void printHashHistogram(const ELFFile<ELFT> *Obj) override;
void printCGProfile(const ELFFile<ELFT> *Obj) override;
void printAddrsig(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;
@ -448,6 +454,7 @@ public:
void printSectionAsString(const ELFO *Obj, StringRef SectionName) override;
void printHashHistogram(const ELFFile<ELFT> *Obj) override;
void printCGProfile(const ELFFile<ELFT> *Obj) override;
void printAddrsig(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;
@ -1441,6 +1448,12 @@ ELFDumper<ELFT>::ELFDumper(const ELFFile<ELFT> *Obj, ScopedPrinter &Writer)
if (DotCGProfileSec != nullptr)
reportError("Multiple .note.llvm.cgprofile");
DotCGProfileSec = &Sec;
break;
case ELF::SHT_LLVM_ADDRSIG:
if (DotAddrsigSec != nullptr)
reportError("Multiple .llvm_addrsig");
DotAddrsigSec = &Sec;
break;
}
}
@ -2460,6 +2473,10 @@ template <class ELFT> void ELFDumper<ELFT>::printGroupSections() {
ELFDumperStyle->printGroupSections(Obj);
}
template <class ELFT> void ELFDumper<ELFT>::printAddrsig() {
ELFDumperStyle->printAddrsig(Obj);
}
static inline void printFields(formatted_raw_ostream &OS, StringRef Str1,
StringRef Str2) {
OS.PadToColumn(2u);
@ -2840,6 +2857,8 @@ std::string getSectionTypeString(unsigned Arch, unsigned Type) {
return "LLVM_LINKER_OPTIONS";
case SHT_LLVM_CALL_GRAPH_PROFILE:
return "LLVM_CALL_GRAPH_PROFILE";
case SHT_LLVM_ADDRSIG:
return "LLVM_ADDRSIG";
// FIXME: Parse processor specific GNU attributes
case SHT_GNU_ATTRIBUTES:
return "ATTRIBUTES";
@ -3541,6 +3560,11 @@ void GNUStyle<ELFT>::printCGProfile(const ELFFile<ELFT> *Obj) {
OS << "GNUStyle::printCGProfile not implemented\n";
}
template <class ELFT>
void GNUStyle<ELFT>::printAddrsig(const ELFFile<ELFT> *Obj) {
OS << "GNUStyle::printAddrsig not implemented\n";
}
static std::string getGNUNoteTypeName(const uint32_t NT) {
static const struct {
uint32_t ID;
@ -4407,6 +4431,27 @@ void LLVMStyle<ELFT>::printCGProfile(const ELFFile<ELFT> *Obj) {
}
}
template <class ELFT>
void LLVMStyle<ELFT>::printAddrsig(const ELFFile<ELFT> *Obj) {
ListScope L(W, "Addrsig");
if (!this->dumper()->getDotAddrsigSec())
return;
ArrayRef<uint8_t> Contents = unwrapOrError(
Obj->getSectionContents(this->dumper()->getDotAddrsigSec()));
const uint8_t *Cur = Contents.begin();
const uint8_t *End = Contents.end();
while (Cur != End) {
unsigned Size;
const char *Err;
uint64_t SymIndex = decodeULEB128(Cur, &Size, Contents.end(), &Err);
if (Err)
reportError(Err);
W.printNumber("Sym", this->dumper()->getStaticSymbolName(SymIndex),
SymIndex);
Cur += Size;
}
}
template <class ELFT>
void LLVMStyle<ELFT>::printNotes(const ELFFile<ELFT> *Obj) {
W.startLine() << "printNotes not implemented!\n";

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

@ -52,6 +52,7 @@ public:
virtual void printGroupSections() {}
virtual void printHashHistogram() {}
virtual void printCGProfile() {}
virtual void printAddrsig() {}
virtual void printNotes() {}
virtual void printELFLinkerOptions() {}

5
tools/llvm-readobj/llvm-readobj.cpp
View File

@ -302,6 +302,9 @@ namespace opts {
cl::opt<bool> CGProfile("elf-cg-profile", cl::desc("Display callgraph profile section"));
cl::opt<bool> Addrsig("elf-addrsig",
cl::desc("Display address-significance table"));
cl::opt<OutputStyleTy>
Output("elf-output-style", cl::desc("Specify ELF dump style"),
cl::values(clEnumVal(LLVM, "LLVM default style"),
@ -469,6 +472,8 @@ static void dumpObject(const ObjectFile *Obj, ScopedPrinter &Writer) {
Dumper->printHashHistogram();
if (opts::CGProfile)
Dumper->printCGProfile();
if (opts::Addrsig)
Dumper->printAddrsig();
if (opts::Notes)
Dumper->printNotes();
}