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

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

Differential Revision: https://reviews.llvm.org/D113466

Author: MaskRay

lld/ELF/InputFiles.cpp

@@ -837,21 +837,25 @@ template <class ELFT> static uint32_t readAndFeatures(const InputSection &sec) {
 }
 
 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];
-
-  // 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");
-  return target;
+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 != 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
@@ -939,7 +943,7 @@ InputSectionBase *ObjFile<ELFT>::createInputSection(uint32_t idx,
     // 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;
 

lld/ELF/InputFiles.h

@@ -259,7 +259,8 @@ template <class ELFT> class ObjFile : public ELFFileBase {
   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);
 

lld/test/ELF/invalid-relocations.test

@@ -1,6 +1,6 @@
 # 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:
@@ -25,7 +25,7 @@ Symbols:
 
 # 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: