[ELF] Don't suggest alternative spelling of an empty name

Fix PR50111

Differential Revision: https://reviews.llvm.org/D101698

Author: MaskRay

lld/ELF/Relocations.cpp

@@ -763,7 +763,7 @@ static const Symbol *getAlternativeSpelling(const Undefined &sym,
 
     // Build a map of local defined symbols.
     for (const Symbol *s : sym.file->getSymbols())
-      if (s->isLocal() && s->isDefined())
+      if (s->isLocal() && s->isDefined() && !s->getName().empty())
         map.try_emplace(s->getName(), s);
   }
 

lld/test/ELF/undef-not-suggest.test

@@ -52,3 +52,31 @@ Symbols:
     Section: .text.foo
   - Name:    for
     Section: .data
+
+## Check we don't suggest an empty name symbol (e.g. STT_SECTION).
+
+# RUN: yaml2obj --docnum=2 %s -o %t2.o
+# RUN: not ld.lld %t2.o -o /dev/null 2>&1 | FileCheck %s
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name:  .text
+    Type:  SHT_PROGBITS
+    Flags: [ SHF_ALLOC, SHF_EXECINSTR ]
+  - Name: .rela.text
+    Type:  SHT_RELA
+    Info: .text
+    Relocations:
+      - Type:   R_X86_64_64
+        Symbol: f
+Symbols:
+  - Name:    ""
+    Type:    STT_SECTION
+    Section: .text
+  - Name:    f
+    Binding: STB_GLOBAL