[ELF] Suppress "duplicate symbol" when resolving STB_WEAK and STB_GNU_UNIQUE in diffe...

```
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

(cherry picked from commit 0051b6bb78772b0658f28e5f31ddf91c1589aab5)

diff --git a/lld/ELF/InputFiles.cpp b/lld/ELF/InputFiles.cpp
index 927dc272b53269dadb42118ac67b84dfa125f537..473809b05e9c2a3f5ac86a32d0e0f97376e219b7 100644 (file)
--- a/lld/ELF/InputFiles.cpp
+++ b/lld/ELF/InputFiles.cpp
@@ -1157,7 +1157,7 @@ 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});

diff --git a/lld/test/ELF/comdat-binding2.s b/lld/test/ELF/comdat-binding2.s
new file mode 100644 (file)
index 0000000..3ffd725
--- /dev/null
+++ b/lld/test/ELF/comdat-binding2.s
@@ -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