Discard local symbols from SHF_MERGE sections.

This matches the behavior of both gold and bfd ld.

llvm-svn: 255355

lld/ELF/OutputSections.cpp

@@ -1168,15 +1168,26 @@ bool lld::elf2::shouldKeepInSymtab(const ObjectFile<ELFT> &File,
   if (Sym.getType() == STT_SECTION)
     return false;
 
+  InputSectionBase<ELFT> *Sec = File.getSection(Sym);
   // If sym references a section in a discarded group, don't keep it.
-  if (File.getSection(Sym) == &InputSection<ELFT>::Discarded)
+  if (Sec == &InputSection<ELFT>::Discarded)
     return false;
 
   if (Config->DiscardNone)
     return true;
 
-  // ELF defines dynamic locals as symbols which name starts with ".L".
+  // In ELF assembly .L symbols are normally discarded by the assembler.
-  return !(Config->DiscardLocals && SymName.startswith(".L"));
+  // If the assembler fails to do so, the linker discards them if
+  // * --discard-locals is used.
+  // * The symbol is in a SHF_MERGE section, which is normally the reason for
+  //   the assembler keeping the .L symbol.
+  if (!SymName.startswith(".L"))
+    return true;
+
+  if (Config->DiscardLocals)
+    return false;
+
+  return !(Sec->getSectionHdr()->sh_flags & SHF_MERGE);
 }
 
 template <class ELFT>

lld/test/ELF/discard-merge-locals.s

@@ -0,0 +1,24 @@
+// RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t
+// RUN: ld.lld %t -o %t2 -shared
+// RUN: llvm-readobj -t %t2 | FileCheck %s
+// REQUIRES: x86
+
+	leaq	.L.str(%rip), %rdi
+
+	.section	.rodata.str1.1,"aMS",@progbits,1
+.L.str:
+	.asciz	"foobar"
+
+// Test that the .L symbol is omitted
+
+// CHECK:      Symbols [
+// CHECK-NEXT:   Symbol {
+// CHECK-NEXT:     Name:  (0)
+// CHECK-NEXT:     Value: 0x0
+// CHECK-NEXT:     Size: 0
+// CHECK-NEXT:     Binding: Local
+// CHECK-NEXT:     Type: None
+// CHECK-NEXT:     Other: 0
+// CHECK-NEXT:     Section: Undefined
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]