[PATCH] D61712: [ELF] Initialize Target before it may be referenced by findAux when reporting "duplicate symbol" error

[Fangrui Song via Phabricator via llvm-commits]

MaskRay created this revision.
MaskRay added a reviewer: ruiu.
Herald added subscribers: llvm-commits, atanasyan, arichardson, aprantl, sdardis, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.

  for (InputFile *F : Files)
    Symtab->addFile<ELFT>(F); // if there is a duplicate symbol error
  
  ...
  
  Target = getTarget();

When parsing .debug_info in the object file (for better diagnostics),
DWARF.cpp findAux may dereference the null pointer Target

  auto *DR = dyn_cast<Defined>(&File->getRelocTargetSym(Rel));
  if (!DR) { /// Some asan object files contain R_X86_64_NONE
    RelType Type = Rel.getType(Config->IsMips64EL);
    if (Type != Target->NoneRel) /// Target is null

Move the assignment of Target to an earlier place to fix this.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D61712

Files:
  ELF/Driver.cpp
  test/ELF/undef-broken-debug.test


Index: test/ELF/undef-broken-debug.test
===================================================================
--- test/ELF/undef-broken-debug.test
+++ test/ELF/undef-broken-debug.test
@@ -8,6 +8,10 @@
 # CHECK: error: {{.*}}.o: relocation R_X86_64_64 at 0x29 has unsupported target
 # CHECK: error: undefined symbol: bar
 
+# We used to dereference null Target in DWARF.cpp:findAux while reporting a duplicate symbol error,
+# because Target wasn't initialized yet.
+# RUN: not ld.lld %t.o %t.o -o /dev/null
+
 --- !ELF
 FileHeader:
   Class:           ELFCLASS64
Index: ELF/Driver.cpp
===================================================================
--- ELF/Driver.cpp
+++ ELF/Driver.cpp
@@ -440,6 +440,11 @@
   if (errorCount())
     return;
 
+  // The Target instance handles target-specific stuff, such as applying
+  // relocations or writing a PLT section. It also contains target-dependent
+  // values such as a default image base address.
+  Target = getTarget();
+
   switch (Config->EKind) {
   case ELF32LEKind:
     link<ELF32LE>(Args);
@@ -1616,11 +1621,6 @@
   if (Config->Strip != StripPolicy::None)
     llvm::erase_if(InputSections, [](InputSectionBase *S) { return S->Debug; });
 
-  // The Target instance handles target-specific stuff, such as applying
-  // relocations or writing a PLT section. It also contains target-dependent
-  // values such as a default image base address.
-  Target = getTarget();
-
   Config->EFlags = Target->calcEFlags();
   Config->MaxPageSize = getMaxPageSize(Args);
   Config->ImageBase = getImageBase(Args);


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