[llvm] 329a675 - ELFObjectWriter: Simplify STT_SECTION adjustment. NFC
Fangrui Song via llvm-commits
llvm-commits at lists.llvm.org
Sat Apr 12 20:54:10 PDT 2025
Author: Fangrui Song
Date: 2025-04-12T20:54:05-07:00
New Revision: 329a675006a22da89ca39199fac4408e3ae4eee4
URL: https://github.com/llvm/llvm-project/commit/329a675006a22da89ca39199fac4408e3ae4eee4
DIFF: https://github.com/llvm/llvm-project/commit/329a675006a22da89ca39199fac4408e3ae4eee4.diff
LOG: ELFObjectWriter: Simplify STT_SECTION adjustment. NFC
Added:
Modified:
llvm/include/llvm/MC/MCELFObjectWriter.h
llvm/lib/MC/ELFObjectWriter.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/MC/MCELFObjectWriter.h b/llvm/include/llvm/MC/MCELFObjectWriter.h
index 3b7a0c8a70257..f0f2dca4738e4 100644
--- a/llvm/include/llvm/MC/MCELFObjectWriter.h
+++ b/llvm/include/llvm/MC/MCELFObjectWriter.h
@@ -182,9 +182,9 @@ class ELFObjectWriter final : public MCObjectWriter {
bool hasRelocationAddend() const;
bool usesRela(const MCTargetOptions *TO, const MCSectionELF &Sec) const;
- bool shouldRelocateWithSymbol(const MCAssembler &Asm, const MCValue &Val,
- const MCSymbolELF *Sym, uint64_t C,
- unsigned Type) const;
+ bool useSectionSymbol(const MCAssembler &Asm, const MCValue &Val,
+ const MCSymbolELF *Sym, uint64_t C,
+ unsigned Type) const;
bool checkRelocation(MCContext &Ctx, SMLoc Loc, const MCSectionELF *From,
const MCSectionELF *To);
diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index 23d5517920e7b..75450aa7de9d9 100644
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -1246,53 +1246,15 @@ void ELFObjectWriter::executePostLayoutBinding(MCAssembler &Asm) {
// It is always valid to create a relocation with a symbol. It is preferable
// to use a relocation with a section if that is possible. Using the section
// allows us to omit some local symbols from the symbol table.
-bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
- const MCValue &Val,
- const MCSymbolELF *Sym,
- uint64_t C,
- unsigned Type) const {
- // A PCRel relocation to an absolute value has no symbol (or section). We
- // represent that with a relocation to a null section.
- if (!Val.getAddSym())
- return false;
-
- // An undefined symbol is not in any section, so the relocation has to point
- // to the symbol itself.
- assert(Sym && "Expected a symbol");
- if (Sym->isUndefined()) {
- // The .odp creation emits a relocation against the symbol ".TOC." which
- // create a R_PPC64_TOC relocation. However the relocation symbol name
- // in final object creation should be NULL, since the symbol does not
- // really exist, it is just the reference to TOC base for the current
- // object file. Since the symbol is undefined, returning false results
- // in a relocation with a null section which is the desired result.
- return !(Type == ELF::R_PPC64_TOC &&
- TargetObjectWriter->getEMachine() == ELF::EM_PPC64);
- }
-
- unsigned Binding = Sym->getBinding();
- switch(Binding) {
- default:
- llvm_unreachable("Invalid Binding");
- case ELF::STB_LOCAL:
- break;
- case ELF::STB_WEAK:
- // If the symbol is weak, it might be overridden by a symbol in another
- // file. The relocation has to point to the symbol so that the linker
- // can update it.
- return true;
- case ELF::STB_GLOBAL:
- case ELF::STB_GNU_UNIQUE:
- // Global ELF symbols can be preempted by the dynamic linker. The relocation
- // has to point to the symbol for a reason analogous to the STB_WEAK case.
- return true;
- }
-
+bool ELFObjectWriter::useSectionSymbol(const MCAssembler &Asm,
+ const MCValue &Val,
+ const MCSymbolELF *Sym, uint64_t C,
+ unsigned Type) const {
// Keep symbol type for a local ifunc because it may result in an IRELATIVE
// reloc that the dynamic loader will use to resolve the address at startup
// time.
if (Sym->getType() == ELF::STT_GNU_IFUNC)
- return true;
+ return false;
// If a relocation points to a mergeable section, we have to be careful.
// If the offset is zero, a relocation with the section will encode the
@@ -1306,13 +1268,13 @@ bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
unsigned Flags = Sec.getFlags();
if (Flags & ELF::SHF_MERGE) {
if (C != 0)
- return true;
+ return false;
// gold<2.34 incorrectly ignored the addend for R_386_GOTOFF (9)
// (http://sourceware.org/PR16794).
if (TargetObjectWriter->getEMachine() == ELF::EM_386 &&
Type == ELF::R_386_GOTOFF)
- return true;
+ return false;
// ld.lld handles R_MIPS_HI16/R_MIPS_LO16 separately, not as a whole, so
// it doesn't know that an R_MIPS_HI16 with implicit addend 1 and an
@@ -1323,7 +1285,7 @@ bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
// symbol for this case as well.
if (TargetObjectWriter->getEMachine() == ELF::EM_MIPS &&
!hasRelocationAddend())
- return true;
+ return false;
}
// Most TLS relocations use a got, so they need the symbol. Even those that
@@ -1331,7 +1293,7 @@ bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
// 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
// http://sourceware.org/PR16773.
if (Flags & ELF::SHF_TLS)
- return true;
+ return false;
}
// If the symbol is a thumb function the final relocation must set the lowest
@@ -1339,11 +1301,9 @@ bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
// set, so we would lose the bit if we relocated with the section.
// FIXME: We could use the section but add the bit to the relocation value.
if (Asm.isThumbFunc(Sym))
- return true;
+ return false;
- if (TargetObjectWriter->needsRelocateWithSymbol(Val, *Sym, Type))
- return true;
- return false;
+ return !TargetObjectWriter->needsRelocateWithSymbol(Val, *Sym, Type);
}
bool ELFObjectWriter::checkRelocation(MCContext &Ctx, SMLoc Loc,
@@ -1425,17 +1385,19 @@ void ELFObjectWriter::recordRelocation(MCAssembler &Asm,
return;
unsigned Type = TargetObjectWriter->getRelocType(Ctx, Target, Fixup, IsPCRel);
- const auto *Parent = cast<MCSectionELF>(Fragment->getParent());
- // Emiting relocation with sybmol for CG Profile to help with --cg-profile.
- bool RelocateWithSymbol =
- shouldRelocateWithSymbol(Asm, Target, SymA, C, Type) ||
- (Parent->getType() == ELF::SHT_LLVM_CALL_GRAPH_PROFILE);
- uint64_t Addend = !RelocateWithSymbol && SymA && !SymA->isUndefined()
- ? C + Asm.getSymbolOffset(*SymA)
- : C;
- FixedValue = usesRela(TO, FixupSection) ? 0 : Addend;
+ bool UseSectionSym =
+ SymA && SymA->getBinding() == ELF::STB_LOCAL && !SymA->isUndefined();
+ if (UseSectionSym) {
+ UseSectionSym = useSectionSymbol(Asm, Target, SymA, C, Type);
+
+ // Disable STT_SECTION adjustment for CG Profile to help with --cg-profile.
+ const auto *Parent = cast<MCSectionELF>(Fragment->getParent());
+ UseSectionSym &= Parent->getType() != ELF::SHT_LLVM_CALL_GRAPH_PROFILE;
+ }
- if (!RelocateWithSymbol) {
+ uint64_t Addend = UseSectionSym ? C + Asm.getSymbolOffset(*SymA) : C;
+ FixedValue = usesRela(TO, FixupSection) ? 0 : Addend;
+ if (UseSectionSym) {
const auto *SectionSymbol =
SecA ? cast<MCSymbolELF>(SecA->getBeginSymbol()) : nullptr;
if (SectionSymbol)
@@ -1445,6 +1407,12 @@ void ELFObjectWriter::recordRelocation(MCAssembler &Asm,
return;
}
+ // In PPC64 ELFv1, .quad .TOC. at tocbase in the .opd section is expected to
+ // reference the null symbol.
+ if (Type == ELF::R_PPC64_TOC &&
+ TargetObjectWriter->getEMachine() == ELF::EM_PPC64)
+ SymA = nullptr;
+
const MCSymbolELF *RenamedSymA = SymA;
if (SymA) {
if (const MCSymbolELF *R = Renames.lookup(SymA))
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