[ELF] - Fix error reporting with --strip-debug/--strip-all.

[grimar]

Summary

Currently LLD tries to use information about functions and variables location
taking it from debug sections. When --strip-* is given we discard such sections
and that breaks error reporting.
Patch stops discarding such sections and just removes them from InputSections list.

[ruiu]

I don't think it is a good idea to remove debug sections using the garbage collector. That is unnecessarily complicated. You should simply remove debug sections from InputSections before markLive().

[grimar]

• Changed implementation.

[ruiu]

LGTM

It's now much better.

ELF/Driver.cpp

1120–1122 ↗

(On Diff #121443)

Just the first half should suffice.

// We do not want to emit debug sections if --strip-all or -strip-debug are given.

lld/trunk/ELF/Driver.cpp

template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
   for (InputFile *F : ObjectFiles)
     for (InputSectionBase *S : F->getSections())
       if (S && S != &InputSection::Discarded)
         InputSections.push_back(S);
   for (BinaryFile *F : BinaryFiles)
     for (InputSectionBase *S : F->getSections())
       InputSections.push_back(cast<InputSection>(S));
 
+  // We do not want to emit debug sections if --strip-all
+  // or -strip-debug are given.
+  if (Config->Strip != StripPolicy::None)
+    llvm::erase_if(InputSections, [](InputSectionBase *S) {
+      return S->Name.startswith(".debug") || S->Name.startswith(".zdebug");
+    });
+
   Config->EFlags = Target->calcEFlags();
 
   // This adds a .comment section containing a version string. We have to add it
   // before decompressAndMergeSections because the .comment section is a
   // mergeable section.
   if (!Config->Relocatable)
     InputSections.push_back(createCommentSection<ELFT>());
 

lld/trunk/ELF/InputFiles.cpp

InputSectionBase *ObjFile<ELFT>::createInputSection(const Elf_Shdr &Sec) {
   // Only GNU gold supports that. We don't. For the details about that,
   // see https://gcc.gnu.org/wiki/SplitStacks
   if (Name == ".note.GNU-split-stack") {
     error(toString(this) +
           ": object file compiled with -fsplit-stack is not supported");
     return &InputSection::Discarded;
   }
 
-  if (Config->Strip != StripPolicy::None &&
-      (Name.startswith(".debug") || Name.startswith(".zdebug")))
-    return &InputSection::Discarded;
-
   // The linkonce feature is a sort of proto-comdat. Some glibc i386 object
   // files contain definitions of symbol "__x86.get_pc_thunk.bx" in linkonce
   // sections. Drop those sections to avoid duplicate symbol errors.
   // FIXME: This is glibc PR20543, we should remove this hack once that has been
   // fixed for a while.
   if (Name.startswith(".gnu.linkonce."))
     return &InputSection::Discarded;
 

lld/trunk/test/ELF/conflict-debug-variable.s

 # CHECK-NEXT: >>> defined at 1.c:2
 # CHECK-NEXT: >>>            {{.*}}:(.data+0x0)
 # CHECK:      duplicate symbol: foo
 # CHECK-NEXT: >>> defined at 1.c:1
 # CHECK-NEXT: >>>            {{.*}}:(foo)
 # CHECK-NEXT: >>> defined at 1.c:1
 # CHECK-NEXT: >>>            {{.*}}:(.bss+0x0)
 
+## Check that stripping debug sections does not break error reporting.
+# RUN: not ld.lld --strip-debug %t.o %t.o -o %t 2>&1 | FileCheck %s
+
 # Used reduced output from following code and gcc 7.1.0
 # to produce this input file:
 # Source (1.c):
 #  int foo = 0;
 #  int bar = 1;
 # Invocation: g++ -g -S 1.c
 
 .bss