[lld] 0051b6b - [ELF] Suppress "duplicate symbol" when resolving STB_WEAK and STB_GNU_UNIQUE in different COMDATs

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2022-10-21T09:43:25-07:00
New Revision: 0051b6bb78772b0658f28e5f31ddf91c1589aab5

URL: https://github.com/llvm/llvm-project/commit/0051b6bb78772b0658f28e5f31ddf91c1589aab5
DIFF: https://github.com/llvm/llvm-project/commit/0051b6bb78772b0658f28e5f31ddf91c1589aab5.diff

LOG: [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

Added: 
    lld/test/ELF/comdat-binding2.s

Modified: 
    lld/ELF/InputFiles.cpp

Removed: 
    


################################################################################
diff  --git a/lld/ELF/InputFiles.cpp b/lld/ELF/InputFiles.cpp
index 4550beff5243b..85168889b5f04 100644
--- a/lld/ELF/InputFiles.cpp
+++ b/lld/ELF/InputFiles.cpp
@@ -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});

diff  --git a/lld/test/ELF/comdat-binding2.s b/lld/test/ELF/comdat-binding2.s
new file mode 100644
index 0000000000000..3ffd7252836c9
--- /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, at object
+	.section	.bss._ZN1BIiE1aE,"aGwR", at nobits,_ZN1BIiE1aE,comdat
+	.weak	_ZN1BIiE1aE
+_ZN1BIiE1aE:
+	.zero	4
+
+	.type	_ZGVN1BIiE1aE, at object
+	.section	.bss._ZGVN1BIiE1aE,"aGw", at nobits,_ZN1BIiE1aE,comdat
+	.weak	_ZGVN1BIiE1aE
+_ZGVN1BIiE1aE:
+	.quad	0
+
+#--- unique.s
+## GCC -fgnu-unique. Note the 
diff erent group signature for the second group.
+	.weak	_ZN1BIiE1aE
+	.section	.bss._ZN1BIiE1aE,"awG", at nobits,_ZN1BIiE1aE,comdat
+	.type	_ZN1BIiE1aE, @gnu_unique_object
+_ZN1BIiE1aE:
+	.zero	4
+
+	.weak	_ZGVN1BIiE1aE
+	.section	.bss._ZGVN1BIiE1aE,"awG", at nobits,_ZGVN1BIiE1aE,comdat
+	.type	_ZGVN1BIiE1aE, @gnu_unique_object
+_ZGVN1BIiE1aE:
+	.zero	8