[all-commits] [llvm/llvm-project] 0051b6: [ELF] Suppress "duplicate symbol" when resolving S...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 0051b6bb78772b0658f28e5f31ddf91c1589aab5
      https://github.com/llvm/llvm-project/commit/0051b6bb78772b0658f28e5f31ddf91c1589aab5
  Author: Fangrui Song <i at maskray.me>
  Date:   2022-10-21 (Fri, 21 Oct 2022)

  Changed paths:
    M lld/ELF/InputFiles.cpp
    A lld/test/ELF/comdat-binding2.s

  Log Message:
  -----------
  [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