[LLD] cleans up context and symbol table to allow multiple invocations to lld::elf::linker()

[MaskRay]

Summary

Fixes: https://github.com/llvm/llvm-project/issues/59874

Initially after the first invocation of the linker() the symbol table is not cleared and this causes issues with the second invocation when linking a new shared library due to a conflict in the presence of a previously existing _DYNAMIC symbol tripping a runtime assertion.
The linker already had a cleanup lambda registered in an error handler. This patch just declares that lambda up front, and calls it before registering in the error handler. This way the linker can be called multiple times. This is necessary when JIT-ing e.g. AMDGCN kernels.

[jhuber6]

This looks reasonable to me. I'd like to hear if @MaskRay has any objections. Thanks for submitting a bug fix!

[bjoo]

Thanks @jhuber6 . My only remaining concern is that this is a bit of a blunt instrument. I am not sure for example whether the new symtap creation causes a leak ultimately. If more knowledgeable folks than I can suggest refinements I'd be happy to implement them.

[MaskRay]

(Back from a trip)
This is not a proper fix. After D108850 the user of lld::elf::link now needs to manually invoke CommonLinkerContext::destroy(); (see lld/tools/lld/lld.cpp).
I agree that requiring another function call is not that ergonomic but I think we need a better solution instead of landing this.

[MaskRay]

I am working on a better fix.

[MaskRay]

D142949

[aganea]

As mentioned in https://github.com/llvm/llvm-project/issues/59874, this is on purpose. More info here: https://reviews.llvm.org/D142949#4093346. One should call safeLldMain() instead! Let me finish/land D119049 and things should look better afterwards.

[MaskRay]

Obsoleted by D119049

lld/ELF/Driver.cpp

 }
 
 bool elf::link(ArrayRef<const char *> args, llvm::raw_ostream &stdoutOS,
                llvm::raw_ostream &stderrOS, bool exitEarly,
                bool disableOutput) {
   // This driver-specific context will be freed later by lldMain().
   auto *ctx = new CommonLinkerContext;
 
-  ctx->e.initialize(stdoutOS, stderrOS, exitEarly, disableOutput);
-  ctx->e.cleanupCallback = []() {
+  auto cleanup = []() {
     elf::ctx.reset();
     symtab = SymbolTable();
 
     outputSections.clear();
     symAux.clear();
 
     tar = nullptr;
     in.reset();
 
     partitions.clear();
     partitions.emplace_back();
 
     SharedFile::vernauxNum = 0;
   };
+
+  // Clears leftovers from any previous invocation
+  cleanup();
+
+  ctx->e.initialize(stdoutOS, stderrOS, exitEarly, disableOutput);
+  ctx->e.cleanupCallback = cleanup;
+
   ctx->e.logName = args::getFilenameWithoutExe(args[0]);
   ctx->e.errorLimitExceededMsg = "too many errors emitted, stopping now (use "
                                  "--error-limit=0 to see all errors)";
 
   config = ConfigWrapper();
   script = std::make_unique<LinkerScript>();
 
   symAux.emplace_back();