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[ELF] Suppress "duplicate symbol" when resolving STB_WEAK and STB_GNU_UNIQUE in different COMDATs 

```
template <typename T> struct A {
  A() {}
  int value = 0;
};

template <typename Value> struct B {
  static A<int> a;
};

template <typename Value> A<int> B<Value>::a;

inline int foo() {
  return B<int>::a.value;
}
```

```
clang++ -c -fno-pic a.cc -o weak.o
g++ -c -fno-pic a.cc -o unique.o  # --enable-gnu-unique-object

# Duplicate symbol error. In postParse, we do not check `sym.binding`
ld.lld -e 0 weak.o unique.o
```

Mixing GCC and Clang object files in this case is not ideal. .bss._ZGVN1BIiE1aE
has different COMDAT groups. It appears to work in practice because the guard
variable prevents harm due to double initialization.

For the linker, we just stick with the rule that a weak binding does not cause
"duplicate symbol" errors.

Close https://github.com/llvm/llvm-project/issues/58232

Differential Revision: https://reviews.llvm.org/D136381
This commit is contained in:
Fangrui Song 2022-10-21 09:43:25 -07:00
parent 461a1836d3
commit 0051b6bb78
2 changed files with 43 additions and 1 deletions
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2
lld/ELF/InputFiles.cpp
View File

@ -1190,7 +1190,7 @@ template <class ELFT> void ObjFile<ELFT>::postParse() {
continue;
}
if (binding == STB_WEAK)
if (sym.binding == STB_WEAK || binding == STB_WEAK)
continue;
std::lock_guard<std::mutex> lock(mu);
ctx.duplicates.push_back({&sym, this, sec, eSym.st_value});

42
lld/test/ELF/comdat-binding2.s Normal file
View File

@ -0,0 +1,42 @@
# REQUIRES: x86
## Test we don't report duplicate definition errors when mixing Clang STB_WEAK
## and GCC STB_GNU_UNIQUE symbols.
# RUN: rm -rf %t && split-file %s %t && cd %t
# RUN: llvm-mc -filetype=obj -triple=x86_64 weak.s -o weak.o
# RUN: llvm-mc -filetype=obj -triple=x86_64 unique.s -o unique.o
# RUN: ld.lld weak.o unique.o -o weak
# RUN: llvm-readelf -s weak | FileCheck %s --check-prefix=WEAK
# RUN: ld.lld unique.o weak.o -o unique
# RUN: llvm-readelf -s unique | FileCheck %s --check-prefix=UNIQUE
# WEAK: OBJECT WEAK DEFAULT [[#]] _ZN1BIiE1aE
# UNIQUE: OBJECT UNIQUE DEFAULT [[#]] _ZN1BIiE1aE
#--- weak.s
## Clang
.type _ZN1BIiE1aE,@object
.section .bss._ZN1BIiE1aE,"aGwR",@nobits,_ZN1BIiE1aE,comdat
.weak _ZN1BIiE1aE
_ZN1BIiE1aE:
.zero 4
.type _ZGVN1BIiE1aE,@object
.section .bss._ZGVN1BIiE1aE,"aGw",@nobits,_ZN1BIiE1aE,comdat
.weak _ZGVN1BIiE1aE
_ZGVN1BIiE1aE:
.quad 0
#--- unique.s
## GCC -fgnu-unique. Note the different group signature for the second group.
.weak _ZN1BIiE1aE
.section .bss._ZN1BIiE1aE,"awG",@nobits,_ZN1BIiE1aE,comdat
.type _ZN1BIiE1aE, @gnu_unique_object
_ZN1BIiE1aE:
.zero 4
.weak _ZGVN1BIiE1aE
.section .bss._ZGVN1BIiE1aE,"awG",@nobits,_ZGVN1BIiE1aE,comdat
.type _ZGVN1BIiE1aE, @gnu_unique_object
_ZGVN1BIiE1aE:
.zero 8