[ELF] Improve sh_info=0 and sh_info>=num_sections diagnostic for SHT_REL/SHT_RELA

[MaskRay]

Summary

PR52408 reported an sh_info=0 instance. I have seen sh_info=0
independently before.

sh_info>=num_sections is probably very rare. Just use one diagnostic for
the two types of errors.

Delete invalid-relocations.test which is covered by invalid/bad-reloc-target.test

[MaskRay]

fatal -> error

[MaskRay]

lld/ELF/InputFiles.cpp

839–840

The hack was from D16898.

[jhenderson]

One suggestion, otherwise LGTM.

lld/ELF/InputFiles.cpp

844

I feel like it might be useful to include the section name here, if it's practical.

[MaskRay]

add section name

lld/ELF/InputFiles.h

public:
   // Get cached DWARF information.
   DWARFCache *getDwarf();
 
 private:
   void initializeSections(bool ignoreComdats);
   void initializeSymbols();
   void initializeJustSymbols();
 
-  InputSectionBase *getRelocTarget(const Elf_Shdr &sec);
+  InputSectionBase *getRelocTarget(uint32_t idx, StringRef name,
+                                   const Elf_Shdr &sec);
   InputSectionBase *createInputSection(uint32_t idx, const Elf_Shdr &sec,
                                        StringRef shstrtab);
 
   bool shouldMerge(const Elf_Shdr &sec, StringRef name);
 
   // Each ELF symbol contains a section index which the symbol belongs to.
   // However, because the number of bits dedicated for that is limited, a
   // symbol can directly point to a section only when the section index is

lld/ELF/InputFiles.cpp

while (!data.empty()) {
 
     // Go to next NOTE record to look for more FEATURE_1_AND descriptions.
     data = data.slice(nhdr->getSize());
   }
 
   return featuresSet;
 }
 
 template <class ELFT>
-InputSectionBase *ObjFile<ELFT>::getRelocTarget(const Elf_Shdr &sec) {
-  uint32_t idx = sec.sh_info;
-  if (idx >= this->sections.size())
-    fatal(toString(this) + ": invalid relocated section index: " + Twine(idx));
-  InputSectionBase *target = this->sections[idx];
+InputSectionBase *ObjFile<ELFT>::getRelocTarget(uint32_t idx, StringRef name,
+                                                const Elf_Shdr &sec) {
+  uint32_t info = sec.sh_info;
+  if (info < this->sections.size()) {
+    InputSectionBase *target = this->sections[info];
 
     // Strictly speaking, a relocation section must be included in the
     // group of the section it relocates. However, LLVM 3.3 and earlier
     // would fail to do so, so we gracefully handle that case.
     if (target == &InputSection::discarded)
       return nullptr;
 
-  if (!target)
-    fatal(toString(this) + ": unsupported relocation reference");
+    if (target != nullptr)
       return target;
   }
 
+  error(toString(this) + Twine(": relocation section ") + name + " (index " +
+        Twine(idx) + ") has invalid sh_info (" + Twine(info) + ")");
+  return nullptr;
+}
+
 // Create a regular InputSection class that has the same contents
 // as a given section.
 static InputSection *toRegularSection(MergeInputSection *sec) {
   return make<InputSection>(sec->file, sec->flags, sec->type, sec->alignment,
                             sec->data(), sec->name);
 }
 
 template <class ELFT>
InputSectionBase *ObjFile<ELFT>::createInputSection(uint32_t idx,
   }
   case SHT_RELA:
   case SHT_REL: {
     // Find a relocation target section and associate this section with that.
     // Target may have been discarded if it is in a different section group
     // and the group is discarded, even though it's a violation of the
     // spec. We handle that situation gracefully by discarding dangling
     // relocation sections.
-    InputSectionBase *target = getRelocTarget(sec);
+    InputSectionBase *target = getRelocTarget(idx, name, sec);
     if (!target)
       return nullptr;
 
     // ELF spec allows mergeable sections with relocations, but they are
     // rare, and it is in practice hard to merge such sections by contents,
     // because applying relocations at end of linking changes section
     // contents. So, we simply handle such sections as non-mergeable ones.
     // Degrading like this is acceptable because section merging is optional.

lld/test/ELF/invalid-relocations.test

-# RUN: yaml2obj %s -o %t
-# RUN: not ld.lld %t -o /dev/null 2>&1 | FileCheck %s
-
-!ELF
-FileHeader:
-  Class:           ELFCLASS64
-  Data:            ELFDATA2LSB
-  Type:            ET_REL
-  Machine:         EM_X86_64
-Sections:
-  - Type:            SHT_PROGBITS
-  - Name:            .rela.text
-    Type:            SHT_RELA
-    Info:            12 # Invalid index
-    Relocations:
-      - Offset:          0x0000000000000001
-        Symbol:          lulz
-        Type:            R_X86_64_PC32
-Symbols:
-  - Name:            lulz
-    Binding:         STB_GLOBAL
-
-# CHECK: invalid relocated section index

lld/test/ELF/invalid/bad-reloc-target.test

 # RUN: yaml2obj --docnum=1 %s -o %t1.o
 # RUN: not ld.lld %t1.o -o /dev/null 2>&1 | FileCheck %s
-# CHECK: error: {{.*}}.o: unsupported relocation reference
+# CHECK: error: {{.*}}.o: relocation section .rela.text (index 2) has invalid sh_info (0)
 
 --- !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
     Link:        .symtab
     Info:        0
     Relocations: 
       - Symbol:  foo
         Type:    R_X86_64_64
 Symbols:         
   - Name:        foo
     Binding:     STB_GLOBAL
 
 # RUN: yaml2obj --docnum=2 %s -o %t2.o
 # RUN: not ld.lld %t2.o -o /dev/null 2>&1 | FileCheck %s --check-prefix=ERR2
-# ERR2: error: {{.*}}.o: invalid relocated section index: 99
+# ERR2: error: {{.*}}.o: relocation section .rela.text (index 2) has invalid sh_info (99)
 
 --- !ELF
 FileHeader:
   Class:         ELFCLASS64
   Data:          ELFDATA2LSB
   Type:          ET_REL
   Machine:       EM_X86_64
 Sections: