[PATCH] D64136: [ELF] resolveUndefined: ignore undefined symbols in SharedFile

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added reviewers: grimar, peter.smith, ruiu.
Herald added subscribers: llvm-commits, jfb, arichardson, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.

libstdc++ std::call_once creates a weak reference of pthread_once.
If %t1.o has a weak reference, %t2.so has a non-weak reference.

ld.lld %t1.o %t2.so -o %t

The reference in %t should be weak.

This fixes an (-z defs) error when linking libLLVMCore.so with lld after D63974 <https://reviews.llvm.org/D63974>.

  ld.lld: error: undefined symbol: pthread_once

Object files with std::call_once calls have weak references of pthread_once.
libLLVMSupport.so.9svn has a non-weak reference that changes the binding. It should be ignored instead.

We happened to work before D63974 <https://reviews.llvm.org/D63974> because libgcc_s.so.1 was linked the last and it changed the binding again to weak.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D64136

Files:
  ELF/Symbols.cpp
  test/ELF/weak-undef-shared.s


Index: test/ELF/weak-undef-shared.s
===================================================================
--- test/ELF/weak-undef-shared.s
+++ test/ELF/weak-undef-shared.s
@@ -24,6 +24,11 @@
 # RUN: ld.lld %t2.o %t.so %t1.o -o %t
 # RUN: llvm-readelf --dyn-syms %t | FileCheck --check-prefix=GLOBAL %s
 
+## Check the binding (weak) is not affected by the STB_GLOBAL undefined
+## reference in %t2.so
+# RUN: ld.lld %t1.o %t2.so -o %t
+# RUN: llvm-readelf --dyn-syms %t | FileCheck --check-prefix=WEAK %s
+
 # WEAK:   NOTYPE WEAK   DEFAULT UND foo
 # GLOBAL: NOTYPE GLOBAL DEFAULT UND foo
 
Index: ELF/Symbols.cpp
===================================================================
--- ELF/Symbols.cpp
+++ ELF/Symbols.cpp
@@ -410,6 +410,10 @@
   if (Traced)
     printTraceSymbol(&Other);
 
+  // Ignore undefined symbols in a SharedFile.
+  if (isa_and_nonnull<SharedFile>(Other.File))
+    return;
+
   if (isUndefined()) {
     // The binding may "upgrade" from weak to non-weak.
     if (Other.Binding != STB_WEAK)


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