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[ELF] Enable parallel relocation scanning for -z nocombreloc and PPC64 (#190309)

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The `bool serial` condition in scanRelocations disabled parallelism for
three cases: -z nocombreloc, MIPS, and PPC64. Resolve two cases:

- nocombreloc: .rela.dyn is now always created with combreloc=true so
  non-relative relocations are sorted deterministically. Since
  #187964 already separates relative relocations unconditionally,
  the only remaining effect of -z nocombreloc is suppressing
  DT_RELACOUNT (gated on ctx.arg.zCombreloc in DynamicSection).

- PPC64: After #181496 moved scanning into scanSectionImpl, the
  sole thread-unsafe access is ctx.ppc64noTocRelax (DenseSet::insert).
  Protect it with ctx.relocMutex, which is already used for rare
  operations during parallel scanning.

MIPS retains serial scanning due to `MipsGotSection` mutations.
This commit is contained in:
Fangrui Song
2026-04-02 22:00:15 -07:00
committed by GitHub
parent bc11c85b6b
commit 2f7bd4fa97
4 changed files with 11 additions and 11 deletions
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4
lld/ELF/Arch/PPC64.cpp
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@@ -1196,8 +1196,10 @@ void PPC64::scanSectionImpl(InputSectionBase &sec, Relocs<RelTy> rels) {
case R_PPC64_TOC16_LO:
// Record the TOC entry (.toc + addend) as not relaxable.
if (sym.isSection() && isa<Defined>(sym) &&
cast<Defined>(sym).section->name == ".toc")
cast<Defined>(sym).section->name == ".toc") {
std::lock_guard<std::mutex> lock(ctx.relocMutex);
ctx.ppc64noTocRelax.insert({&sym, addend});
}
expr = R_GOTREL;
break;
case R_PPC64_TOC16_HA:

8
lld/ELF/Relocations.cpp
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@@ -1184,11 +1184,9 @@ template <class ELFT> void elf::scanRelocations(Ctx &ctx) {
// copy relocations, etc. Note that relocations for non-alloc sections are
// directly processed by InputSection::relocateNonAlloc.
// Deterministic parallellism needs sorting relocations which is unsuitable
// for -z nocombreloc. MIPS and PPC64 use global states which are not suitable
// for parallelism.
bool serial = !ctx.arg.zCombreloc || ctx.arg.emachine == EM_MIPS ||
ctx.arg.emachine == EM_PPC64;
// MIPS modifies MipsGotSection during relocation scanning, which is not
// suitable for parallelism.
bool serial = ctx.arg.emachine == EM_MIPS;
parallel::TaskGroup tg;
auto outerFn = [&]() {
for (ELFFileBase *f : ctx.objectFiles) {

2
lld/ELF/SyntheticSections.cpp
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@@ -4564,7 +4564,7 @@ template <class ELFT> void elf::createSyntheticSections(Ctx &ctx) {
ctx, relaDynName, threadCount);
else
part.relaDyn = std::make_unique<RelocationSection<ELFT>>(
ctx, relaDynName, ctx.arg.zCombreloc, threadCount);
ctx, relaDynName, /*combreloc=*/true, threadCount);
if (ctx.hasDynsym) {
add(*part.dynSymTab);

8
lld/test/ELF/combreloc.s
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@@ -32,11 +32,11 @@
# NOCOMB: Relocations [
# NOCOMB-NEXT: Section ({{.*}}) .rela.dyn {
# NOCOMB-NEXT: 0x3418 R_X86_64_RELATIVE - 0x3420
# NOCOMB-NEXT: 0x33F8 R_X86_64_64 aaa 0x0
# NOCOMB-NEXT: 0x3400 R_X86_64_64 ccc 0x0
# NOCOMB-NEXT: 0x3408 R_X86_64_64 bbb 0x0
# NOCOMB-NEXT: 0x3410 R_X86_64_64 aaa 0x0
# NOCOMB-NEXT: 0x23F0 R_X86_64_GLOB_DAT aaa 0x0
# NOCOMB-NEXT: 0x33F8 R_X86_64_64 aaa 0x0
# NOCOMB-NEXT: 0x3410 R_X86_64_64 aaa 0x0
# NOCOMB-NEXT: 0x3408 R_X86_64_64 bbb 0x0
# NOCOMB-NEXT: 0x3400 R_X86_64_64 ccc 0x0
# NOCOMB-NEXT: }
.globl aaa, bbb, ccc