[obj2yaml] Produce correct output for invalid relocations.

R_X86_64_NONE can be emitted without a symbol associated (well,
in theory it should never be emitted in an ABI-compliant relocatable
object). So, if there's no symbol associated to a reloc, emit one
with an empty name, instead of crashing.

Ack'ed by Michael Spencer offline.

PR: 31768

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293224 91177308-0d34-0410-b5e6-96231b3b80d8

Author: dcci

test/Object/Inputs/invalid-reloc.elf-x86-64

@@ -0,0 +1,37 @@
+RUN: obj2yaml %p/Inputs/invalid-reloc.elf-x86-64 | FileCheck %s
+
+CHECK: --- !ELF
+CHECK-NEXT: FileHeader:
+CHECK-NEXT:   Class:           ELFCLASS64
+CHECK-NEXT:   Data:            ELFDATA2LSB
+CHECK-NEXT:   OSABI:           ELFOSABI_FREEBSD
+CHECK-NEXT:   Type:            ET_REL
+CHECK-NEXT:   Machine:         EM_X86_64
+CHECK-NEXT: Sections:
+CHECK-NEXT:   - Name:            .text
+CHECK-NEXT:     Type:            SHT_PROGBITS
+CHECK-NEXT:     Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+CHECK-NEXT:     AddressAlign:    0x0000000000000004
+CHECK-NEXT:     Content:         4833C0C390
+CHECK-NEXT:   - Name:            .rela.text
+CHECK-NEXT:     Type:            SHT_RELA
+CHECK-NEXT:     Link:            .symtab
+CHECK-NEXT:     AddressAlign:    0x0000000000000008
+CHECK-NEXT:     Info:            .text
+CHECK-NEXT:     Relocations:
+CHECK-NEXT:       - Offset:          0x0000000000000000
+CHECK-NEXT:         Symbol:          ''
+CHECK-NEXT:         Type:            R_X86_64_NONE
+CHECK-NEXT: Symbols:
+CHECK-NEXT:   Local:
+CHECK-NEXT:     - Name:            rb_ary_new_capa
+CHECK-NEXT:       Type:            STT_FUNC
+CHECK-NEXT:       Section:         .text
+CHECK-NEXT:       Size:            0x0000000000000005
+CHECK-NEXT:   Global:
+CHECK-NEXT:     - Name:            __dtraceenabled_ruby___array-create
+CHECK-NEXT:     - Name:            '$dtrace1316529.rb_ary_new_capa'
+CHECK-NEXT:       Type:            STT_FUNC
+CHECK-NEXT:       Section:         .text
+CHECK-NEXT:       Size:            0x0000000000000005
+CHECK-NEXT:       Visibility:      STV_HIDDEN

test/Object/obj2yaml-invalid-reloc.test

@@ -228,10 +228,18 @@ std::error_code ELFDumper<ELFT>::dumpRelocation(const RelT *Rel,
     return errorToErrorCode(StrTabOrErr.takeError());
   StringRef StrTab = *StrTabOrErr;
 
-  Expected<StringRef> NameOrErr = Sym->getName(StrTab);
-  if (!NameOrErr)
-    return errorToErrorCode(NameOrErr.takeError());
-  R.Symbol = NameOrErr.get();
+  if (Sym) {
+    Expected<StringRef> NameOrErr = Sym->getName(StrTab);
+    if (!NameOrErr)
+      return errorToErrorCode(NameOrErr.takeError());
+    R.Symbol = NameOrErr.get();
+  } else {
+    // We have some edge cases of relocations without a symbol associated,
+    // e.g. an object containing the invalid (according to the System V
+    // ABI) R_X86_64_NONE reloc. Create a symbol with an empty name instead
+    // of crashing.
+    R.Symbol = "";
+  }
 
   return obj2yaml_error::success;
 }