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[ELF] Set the priority of STB_GNU_UNIQUE the same as STB_WEAK

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In GCC -fgnu-unique output, STB_GNU_UNIQUE symbols are always defined relative
to a section in a COMDAT group. Currently `other` cannot be STB_GNU_UNIQUE for
valid input, so this patch is NFC.

If we switch to the model that ignores COMDAT resolution when performing symbol
resolution (D120626), this will fix bogus `relocation refers to a symbol in a
discarded section` errors when mixing -fno-gnu-unique objects with -fgnu-unique
objects.

Differential Revision: https://reviews.llvm.org/D120640
This commit is contained in:
Fangrui Song 2022-03-14 12:00:15 -07:00
parent 3466b8e23d
commit c7cf960d85
3 changed files with 40 additions and 1 deletions
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8
lld/ELF/Symbols.cpp
View File

@ -528,7 +528,13 @@ bool Symbol::shouldReplace(const Defined &other) const {
return false;
}
return isWeak() && !other.isWeak();
// Incoming STB_GLOBAL overrides STB_WEAK/STB_GNU_UNIQUE. -fgnu-unique changes
// some vague linkage data in COMDAT from STB_WEAK to STB_GNU_UNIQUE. Treat
// STB_GNU_UNIQUE like STB_WEAK so that we prefer the first among all
// STB_WEAK/STB_GNU_UNIQUE copies. If we prefer an incoming STB_GNU_UNIQUE to
// an existing STB_WEAK, there may be discarded section errors because the
// selected copy may be in a non-prevailing COMDAT.
return !isGlobal() && other.isGlobal();
}
void elf::reportDuplicate(const Symbol &sym, InputFile *newFile,

1
lld/ELF/Symbols.h
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@ -141,6 +141,7 @@ public:
bool includeInDynsym() const;
uint8_t computeBinding() const;
bool isGlobal() const { return binding == llvm::ELF::STB_GLOBAL; }
bool isWeak() const { return binding == llvm::ELF::STB_WEAK; }
bool isUndefined() const { return symbolKind == UndefinedKind; }

32
lld/test/ELF/comdat-binding.s Normal file
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@ -0,0 +1,32 @@
# REQUIRES: x86
# RUN: rm -rf %t && split-file %s %t
# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/g.s -o %t/g.o
# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/w.s -o %t/w.o
# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/u.s -o %t/u.o
# RUN: ld.lld -e 0 %t/w.o %t/u.o -o %t/w
# RUN: llvm-readelf -s %t/w | FileCheck %s --check-prefix=WEAK
# RUN: ld.lld -e 0 %t/u.o %t/w.o -o %t/u
# RUN: llvm-readelf -s %t/u | FileCheck %s --check-prefix=UNIQUE
# RUN: ld.lld -e 0 %t/w.o %t/g.o -o %t/w
# RUN: llvm-readelf -s %t/w | FileCheck %s --check-prefix=WEAK
# WEAK: NOTYPE WEAK DEFAULT [[#]] _ZZ1fvE1x
# UNIQUE: OBJECT UNIQUE DEFAULT [[#]] _ZZ1fvE1x
#--- g.s
movq _ZZ1fvE1x@gotpcrel(%rip), %rax
.section .bss._ZZ1fvE1x,"awG",@nobits,_ZZ1fvE1x,comdat
.globl _ZZ1fvE1x
_ZZ1fvE1x:
#--- w.s
.section .bss._ZZ1fvE1x,"awG",@nobits,_ZZ1fvE1x,comdat
.weak _ZZ1fvE1x
_ZZ1fvE1x:
#--- u.s
.section .bss._ZZ1fvE1x,"awG",@nobits,_ZZ1fvE1x,comdat
.type _ZZ1fvE1x, @gnu_unique_object
_ZZ1fvE1x: