[lld/COFF] Demangle symbol name in discarded section relocation error message (#119726)

Author: nico

lld/COFF/Chunks.cpp

@@ -369,13 +369,14 @@ static void maybeReportRelocationToDiscarded(const SectionChunk *fromChunk,
   // Get the name of the symbol. If it's null, it was discarded early, so we
   // have to go back to the object file.
   ObjFile *file = fromChunk->file;
-  StringRef name;
+  std::string name;
   if (sym) {
-    name = sym->getName();
+    name = toString(file->ctx, *sym);
   } else {
     COFFSymbolRef coffSym =
         check(file->getCOFFObj()->getSymbol(rel.SymbolTableIndex));
-    name = check(file->getCOFFObj()->getSymbolName(coffSym));
+    name = maybeDemangleSymbol(
+        file->ctx, check(file->getCOFFObj()->getSymbolName(coffSym)));
   }
 
   std::vector<std::string> symbolLocations =

lld/COFF/Symbols.cpp

@@ -28,8 +28,8 @@ static_assert(sizeof(SymbolUnion) <= 48,
               "symbols should be optimized for memory usage");
 
 // Returns a symbol name for an error message.
-static std::string maybeDemangleSymbol(const COFFLinkerContext &ctx,
-                                       StringRef symName) {
+std::string maybeDemangleSymbol(const COFFLinkerContext &ctx,
+                                StringRef symName) {
   if (ctx.config.demangle) {
     std::string prefix;
     StringRef prefixless = symName;

lld/COFF/Symbols.h

@@ -533,6 +533,10 @@ std::string toString(const coff::COFFLinkerContext &ctx, coff::Symbol &b);
 std::string toCOFFString(const coff::COFFLinkerContext &ctx,
                          const llvm::object::Archive::Symbol &b);
 
+// Returns a symbol name for an error message.
+std::string maybeDemangleSymbol(const coff::COFFLinkerContext &ctx,
+                                StringRef symName);
+
 } // namespace lld
 
 #endif

lld/test/COFF/reloc-discarded.s

@@ -8,10 +8,15 @@
 
 # RUN: not lld-link -entry:main -nodefaultlib %t1.obj %t2.obj -out:%t.exe -opt:ref   2>&1 | FileCheck %s
 # RUN: not lld-link -entry:main -nodefaultlib %t1.obj %t2.obj -out:%t.exe -opt:noref 2>&1 | FileCheck %s
+# RUN: not lld-link -entry:main -nodefaultlib %t1.obj %t2.obj -out:%t.exe -demangle:no   2>&1 \
+# RUN:     | FileCheck --check-prefix=NODEMANGLE %s
 
-# CHECK: error: relocation against symbol in discarded section: assoc_global
+# CHECK: error: relocation against symbol in discarded section: int __cdecl assoc_global(void)
 # CHECK: >>> referenced by {{.*}}reloc-discarded{{.*}}.obj:(main)
 
+# NODEMANGLE: error: relocation against symbol in discarded section: ?assoc_global@@YAHXZ
+# NODEMANGLE: >>> referenced by {{.*}}reloc-discarded{{.*}}.obj:(main)
+
 	.section	.bss,"bw",discard,main_global
 	.globl	main_global
 	.p2align	2
@@ -20,12 +25,12 @@ main_global:
 
 	.section	.CRT$XCU,"dr",associative,main_global
 	.p2align	3
-assoc_global:
+"?assoc_global@@YAHXZ":
 	.quad	main_global
 
 	.text
 	.globl main
 main:
-	movq assoc_global(%rip), %rax
+	movq "?assoc_global@@YAHXZ"(%rip), %rax
 	movl (%rax), %eax
 	retq