[obj2yaml] - Better dumping for relocations without symbols associated.

[grimar]

Summary

This just reorders the code and removes an assignment
of an empty string for the case when a relocation has
no symbol associated. With this our output becomes
cleaner and shorter.

[MaskRay]

This is a reasonable change to eventually remove the implicit rule of .symtab definition.

tools/obj2yaml/elf2yaml.cpp

416 ↗

(On Diff #225867)

R_X86_64_GOTPC32 and R_PPC64_TOC are examples that use 0 as the symbol index. We probably should not call them "edge cases".

[grimar]

• Addressed review comment.

[MaskRay]

tools/obj2yaml/elf2yaml.cpp

413 ↗

(On Diff #226006)

with symbol index 0.

llvm/test/tools/obj2yaml/elf-ppc64-relocations.yaml

 # CHECK-NEXT:   Machine: EM_PPC64
 # CHECK-NEXT: Sections:
 # CHECK-NEXT:   - Name:    .rela.text
 # CHECK-NEXT:     Type:    SHT_RELA
 # CHECK-NEXT:     Link:    .symtab
 # CHECK-NEXT:     EntSize: 0x0000000000000018
 # CHECK-NEXT:     Relocations:
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_NONE
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR32
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR24
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR16
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR16_LO
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR16_HI
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR16_HA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR14
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR14_BRTAKEN
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR14_BRNTAKEN
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_REL24
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_REL14
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_REL14_BRTAKEN
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_REL14_BRNTAKEN
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT16
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT16_LO
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT16_HI
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT16_HA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GLOB_DAT
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_JMP_SLOT
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_RELATIVE
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_REL32
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR64
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR16_HIGHER
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR16_HIGHERA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR16_HIGHEST
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR16_HIGHESTA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_REL64
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TOC16
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TOC16_LO
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TOC16_HI
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TOC16_HA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TOC
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR16_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR16_LO_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT16_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT16_LO_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TOC16_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TOC16_LO_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TLS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPMOD64
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL16
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL16_LO
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL16_HI
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL16_HA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL64
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL16
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL16_LO
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL16_HI
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL16_HA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL64
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_TLSGD16
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_TLSGD16_LO
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_TLSGD16_HI
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_TLSGD16_HA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_TLSLD16
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_TLSLD16_LO
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_TLSLD16_HI
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_TLSLD16_HA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_TPREL16_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_TPREL16_LO_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_TPREL16_HI
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_TPREL16_HA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_DTPREL16_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_DTPREL16_LO_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_DTPREL16_HI
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_GOT_DTPREL16_HA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL16_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL16_LO_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL16_HIGHER
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL16_HIGHERA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL16_HIGHEST
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL16_HIGHESTA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL16_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL16_LO_DS
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL16_HIGHER
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL16_HIGHERA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL16_HIGHEST
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL16_HIGHESTA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TLSGD
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TLSLD
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR16_HIGH
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_ADDR16_HIGHA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL16_HIGH
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_TPREL16_HIGHA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL16_HIGH
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_DTPREL16_HIGHA
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_IRELATIVE
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_REL16
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_REL16_LO
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_REL16_HI
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_PPC64_REL16_HA
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2MSB
   Type:    ET_REL
   Machine: EM_PPC64

llvm/test/tools/obj2yaml/no-symbol-reloc.test

 # CHECK-NEXT:     Flags:   [ SHF_ALLOC, SHF_EXECINSTR ]
 # CHECK-NEXT:   - Name:    .rela.text
 # CHECK-NEXT:     Type:    SHT_RELA
 # CHECK-NEXT:     Link:    .symtab
 # CHECK-NEXT:     EntSize: 0x0000000000000018
 # CHECK-NEXT:     Info:    .text
 # CHECK-NEXT:     Relocations:
 # CHECK-NEXT:       - Offset: 0x0000000000000000
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_X86_64_NONE
 # CHECK-NEXT:       - Offset: 0x0000000000000004
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   R_X86_64_NONE
 # CHECK-NEXT: Symbols: []
 # CHECK-NEXT: ...
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB

llvm/test/tools/obj2yaml/relocation-unsupported-machine.yaml

 # CHECK-NEXT:   Machine: 0x1234
 # CHECK-NEXT: Sections:
 # CHECK-NEXT:   - Name:    .rela.text
 # CHECK-NEXT:     Type:    SHT_RELA
 # CHECK-NEXT:     Link:    .symtab
 # CHECK-NEXT:     EntSize: 0x0000000000000018
 # CHECK-NEXT:     Relocations:
 # CHECK-NEXT:       - Offset: 0x0000000000000001
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   0x00000002
 # CHECK-NEXT:       - Offset: 0x0000000000000003
-# CHECK-NEXT:         Symbol: ''
 # CHECK-NEXT:         Type:   0x00000004
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2MSB
   Type:    ET_REL
   Machine: 0x1234
 Sections:
   - Name: .rela.text
     Type: SHT_RELA
     Relocations:
       - Offset: 0x1
         Type:   0x2
       - Offset: 0x3
         Type:   0x4

llvm/tools/obj2yaml/elf2yaml.cpp

Error ELFDumper<ELFT>::dumpRelocation(const RelT *Rel, const Elf_Shdr *SymTab,
                                       ELFYAML::Relocation &R) {
   R.Type = Rel->getType(Obj.isMips64EL());
   R.Offset = Rel->r_offset;
   R.Addend = 0;
 
   auto SymOrErr = Obj.getRelocationSymbol(Rel, SymTab);
   if (!SymOrErr)
     return SymOrErr.takeError();
+
+  // We have might have a relocation with symbol index 0,
+  // e.g. R_X86_64_NONE or R_X86_64_GOTPC32.
   const Elf_Sym *Sym = *SymOrErr;
+  if (!Sym)
+    return Error::success();
+
   auto StrTabSec = Obj.getSection(SymTab->sh_link);
   if (!StrTabSec)
     return StrTabSec.takeError();
   auto StrTabOrErr = Obj.getStringTable(*StrTabSec);
   if (!StrTabOrErr)
     return StrTabOrErr.takeError();
-  StringRef StrTab = *StrTabOrErr;
 
-  if (Sym) {
-    Expected<StringRef> NameOrErr = getUniquedSymbolName(Sym, StrTab, SymTab);
-    if (!NameOrErr)
-      return 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 = "";
-  }
+  Expected<StringRef> NameOrErr =
+      getUniquedSymbolName(Sym, *StrTabOrErr, SymTab);
 
   return Error::success();
 }
 
 template <class ELFT>
 Error ELFDumper<ELFT>::dumpCommonSection(const Elf_Shdr *Shdr,
                                          ELFYAML::Section &S) {
   // Dump fields. We do not dump the ShOffset field. When not explicitly