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.gcc_except_table: Set SHF_LINK_ORDER if binutils>=2.36, and drop unneeded unique ID for -fno-unique-section-names

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GNU ld>=2.36 supports mixed SHF_LINK_ORDER and non-SHF_LINK_ORDER sections in an
output section, so we can set SHF_LINK_ORDER if -fbinutils-version=2.36 or above.

If -fno-function-sections or older binutils, drop unique ID for -fno-unique-section-names.
The users can just specify -fbinutils-version=2.36 or above to allow GC with both GNU ld and LLD.
(LLD does not support garbage collection of non-group non-SHF_LINK_ORDER .gcc_except_table sections.)
This commit is contained in:
Fangrui Song 2021-02-05 21:45:21 -08:00
parent fd7d8e9304
commit a98d7fa6b0
5 changed files with 32 additions and 37 deletions
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2
include/llvm/CodeGen/TargetLoweringObjectFileImpl.h
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@ -63,7 +63,7 @@ public:
MCSection *getSectionForJumpTable(const Function &F,
const TargetMachine &TM) const override;
MCSection *getSectionForLSDA(const Function &F,
MCSection *getSectionForLSDA(const Function &F, const MCSymbol &FnSym,
const TargetMachine &TM) const override;
MCSection *

4
include/llvm/Target/TargetLoweringObjectFile.h
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@ -125,8 +125,8 @@ public:
virtual MCSection *getSectionForJumpTable(const Function &F,
const TargetMachine &TM) const;
virtual MCSection *getSectionForLSDA(const Function &F,
const TargetMachine &TM) const {
virtual MCSection *getSectionForLSDA(const Function &, const MCSymbol &,
const TargetMachine &) const {
return LSDASection;
}

4
lib/CodeGen/AsmPrinter/EHStreamer.cpp
View File

@ -420,8 +420,8 @@ MCSymbol *EHStreamer::emitExceptionTable() {
bool HaveTTData = !TypeInfos.empty() || !FilterIds.empty();
// Type infos.
MCSection *LSDASection =
Asm->getObjFileLowering().getSectionForLSDA(MF->getFunction(), Asm->TM);
MCSection *LSDASection = Asm->getObjFileLowering().getSectionForLSDA(
MF->getFunction(), *Asm->CurrentFnSym, Asm->TM);
unsigned TTypeEncoding;
if (!HaveTTData) {

35
lib/CodeGen/TargetLoweringObjectFileImpl.cpp
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@ -834,9 +834,8 @@ MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
/* AssociatedSymbol */ nullptr);
}
MCSection *
TargetLoweringObjectFileELF::getSectionForLSDA(const Function &F,
const TargetMachine &TM) const {
MCSection *TargetLoweringObjectFileELF::getSectionForLSDA(
const Function &F, const MCSymbol &FnSym, const TargetMachine &TM) const {
// If neither COMDAT nor function sections, use the monolithic LSDA section.
// Re-use this path if LSDASection is null as in the Arm EHABI.
if (!LSDASection || (!F.hasComdat() && !TM.getFunctionSections()))
@ -845,30 +844,26 @@ TargetLoweringObjectFileELF::getSectionForLSDA(const Function &F,
const auto *LSDA = cast<MCSectionELF>(LSDASection);
unsigned Flags = LSDA->getFlags();
StringRef Group;
const MCSymbolELF *LinkedToSym = nullptr;
if (F.hasComdat()) {
Group = F.getComdat()->getName();
Flags |= ELF::SHF_GROUP;
}
// Use SHF_LINK_ORDER to facilitate --gc-sections if we can use GNU ld>=2.36
// or LLD, which support mixed SHF_LINK_ORDER & non-SHF_LINK_ORDER.
if (TM.getFunctionSections() &&
(getContext().getAsmInfo()->useIntegratedAssembler() &&
getContext().getAsmInfo()->binutilsIsAtLeast(2, 36))) {
Flags |= ELF::SHF_LINK_ORDER;
LinkedToSym = cast<MCSymbolELF>(&FnSym);
}
// Append the function name as the suffix like GCC, assuming
// -funique-section-names applies to .gcc_except_table sections.
if (TM.getUniqueSectionNames())
return getContext().getELFSection(LSDA->getName() + "." + F.getName(),
LSDA->getType(), Flags, 0, Group,
MCSection::NonUniqueID, nullptr);
// Allocate a unique ID if function sections && (integrated assembler or GNU
// as>=2.35). Note we could use SHF_LINK_ORDER to facilitate --gc-sections but
// that would require that we know the linker is a modern LLD (12.0 or later).
// GNU ld as of 2.35 does not support mixed SHF_LINK_ORDER &
// non-SHF_LINK_ORDER components in an output section
// https://sourceware.org/bugzilla/show_bug.cgi?id=26256
unsigned ID = TM.getFunctionSections() &&
getContext().getAsmInfo()->useIntegratedAssembler()
? NextUniqueID++
: MCSection::NonUniqueID;
return getContext().getELFSection(LSDA->getName(), LSDA->getType(), Flags, 0,
Group, ID, nullptr);
return getContext().getELFSection(
(TM.getUniqueSectionNames() ? LSDA->getName() + "." + F.getName()
: LSDA->getName()),
LSDA->getType(), Flags, 0, Group, MCSection::NonUniqueID, LinkedToSym);
}
bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(

24
test/CodeGen/X86/gcc_except_table-multi.ll
View File

@ -1,10 +1,10 @@
; RUN: llc -simplifycfg-require-and-preserve-domtree=1 < %s -mtriple=x86_64 | FileCheck %s --check-prefixes=CHECK,NORMAL
; RUN: llc -simplifycfg-require-and-preserve-domtree=1 < %s -mtriple=x86_64 -unique-section-names=false | FileCheck %s --check-prefixes=CHECK,NOUNIQUE
; RUN: llc -simplifycfg-require-and-preserve-domtree=1 < %s -mtriple=x86_64 -function-sections | FileCheck %s --check-prefixes=CHECK,SEP
; RUN: llc -simplifycfg-require-and-preserve-domtree=1 < %s -mtriple=x86_64 -function-sections -unique-section-names=false | FileCheck %s --check-prefixes=CHECK,SEP_NOUNIQUE
; RUN: llc -simplifycfg-require-and-preserve-domtree=1 < %s -mtriple=x86_64 -binutils-version=2.35 | FileCheck %s --check-prefixes=CHECK,NORMAL
; RUN: llc -simplifycfg-require-and-preserve-domtree=1 < %s -mtriple=x86_64 -binutils-version=2.36 | FileCheck %s --check-prefixes=CHECK,NORMAL
; RUN: llc -simplifycfg-require-and-preserve-domtree=1 < %s -mtriple=x86_64 -function-sections -binutils-version=2.35 | FileCheck %s --check-prefixes=CHECK,SEP_BFD
; RUN: llc -simplifycfg-require-and-preserve-domtree=1 < %s -mtriple=x86_64 -function-sections -binutils-version=2.36 | FileCheck %s --check-prefixes=CHECK,SEP
;; Don't use `,unique` if GNU as<2.35.
; RUN: llc -simplifycfg-require-and-preserve-domtree=1 < %s -mtriple=x86_64 -function-sections -unique-section-names=false -no-integrated-as | FileCheck %s --check-prefixes=CHECK,SEP_NOUNIQUE_GAS
; RUN: llc -simplifycfg-require-and-preserve-domtree=1 < %s -mtriple=x86_64 -function-sections -unique-section-names=false | FileCheck %s --check-prefixes=CHECK,SEP_NOUNIQUE
; RUN: llc -simplifycfg-require-and-preserve-domtree=1 < %s -mtriple=x86_64 -unique-section-names=false | FileCheck %s --check-prefixes=CHECK,NOUNIQUE
@_ZTIi = external constant i8*
@ -16,10 +16,10 @@ define i32 @group() uwtable comdat personality i8* bitcast (i32 (...)* @__gxx_pe
; CHECK-LABEL: group:
; CHECK: .cfi_endproc
; NORMAL-NEXT: .section .gcc_except_table.group,"aG",@progbits,group,comdat{{$}}
; SEP_BFD-NEXT: .section .gcc_except_table.group,"aG",@progbits,group,comdat{{$}}
; SEP-NEXT: .section .gcc_except_table.group,"aGo",@progbits,group,comdat,group{{$}}
; SEP_NOUNIQUE-NEXT: .section .gcc_except_table,"aG",@progbits,group,comdat{{$}}
; NOUNIQUE-NEXT: .section .gcc_except_table,"aG",@progbits,group,comdat{{$}}
; SEP-NEXT: .section .gcc_except_table.group,"aG",@progbits,group,comdat{{$}}
; SEP_NOUNIQUE-NEXT: .section .gcc_except_table,"aG",@progbits,group,comdat,unique,2
; SEP_NOUNIQUE_GAS-NEXT: .section .gcc_except_table,"aG",@progbits,group,comdat{{$}}
entry:
invoke void @ext() to label %try.cont unwind label %lpad
lpad:
@ -38,10 +38,10 @@ define i32 @foo() uwtable personality i8* bitcast (i32 (...)* @__gxx_personality
; CHECK-LABEL: foo:
; CHECK: .cfi_endproc
; NORMAL-NEXT: .section .gcc_except_table,"a",@progbits{{$}}
; SEP_BFD-NEXT: .section .gcc_except_table.foo,"a",@progbits{{$}}
; SEP-NEXT: .section .gcc_except_table.foo,"ao",@progbits,foo{{$}}
; SEP_NOUNIQUE-NEXT: .section .gcc_except_table,"a",@progbits{{$}}
; NOUNIQUE-NEXT: .section .gcc_except_table,"a",@progbits{{$}}
; SEP-NEXT: .section .gcc_except_table.foo,"a",@progbits{{$}}
; SEP_NOUNIQUE-NEXT: .section .gcc_except_table,"a",@progbits,unique,4
; SEP_NOUNIQUE_GAS-NEXT: .section .gcc_except_table,"a",@progbits{{$}}
entry:
invoke void @ext() to label %try.cont unwind label %lpad
lpad: