[LLD][COFF] When using LLD-as-a-library, always prevent re-entrance on failures

This is a follow-up for D70378 (Cover usage of LLD as a library).

While debugging an intermittent failure on a bot, I recalled this scenario which
causes the issue:

1.When executing lld/test/ELF/invalid/symtab-sh-info.s L45, we reach
  lld::elf::Obj-File::ObjFile() which goes straight into its base ELFFileBase(),
  then ELFFileBase::init().
2.At that point fatal() is thrown in lld/ELF/InputFiles.cpp L381, leaving a
  half-initialized ObjFile instance.
3.We then end up in lld::exitLld() and since we are running with LLD_IN_TEST, we
  hapily restore the control flow to CrashRecoveryContext::RunSafely() then back
  in lld::safeLldMain().
4.Before this patch, we called errorHandler().reset() just after, and this
  attempted to reset the associated SpecificAlloc<ObjFile<ELF64LE>>. That tried
  to free the half-initialized ObjFile instance, and more precisely its
  ObjFile::dwarf member.

Sometimes that worked, sometimes it failed and was catched by the
CrashRecoveryContext. This scenario was the reason we called
errorHandler().reset() through a CrashRecoveryContext.

But in some rare cases, the above repro somehow corrupted the heap, creating a
stack overflow. When the CrashRecoveryContext's filter (that is,
__except (ExceptionFilter(GetExceptionInformation()))) tried to handle the
exception, it crashed again since the stack was exhausted -- and that took the
whole application down. That is the issue seen on the bot. Locally it happens
about 1 times out of 15.

Now this situation can happen anywhere in LLD. Since catching stack overflows is
not a reliable scenario ATM when using CrashRecoveryContext, we're now
preventing further re-entrance when such failures occur, by signaling
lld::SafeReturn::canRunAgain=false. When running with LLD_IN_TEST=2 (or above),
only one iteration will be executed, instead of two.

Differential Revision: https://reviews.llvm.org/D88348

1 files changed, 2 insertions, 11 deletions

diff --git a/lld/tools/lld/lld.cpp b/lld/tools/lld/lld.cpp
index 48d5ae1a0ea0..5d71a8f24adf 100644
--- a/lld/tools/lld/lld.cpp
+++ b/lld/tools/lld/lld.cpp
@@ -179,7 +179,7 @@ SafeReturn lld::safeLldMain(int argc, const char **argv,
     if (!crc.RunSafely([&]() {
           r = lldMain(argc, argv, stdoutOS, stderrOS, /*exitEarly=*/false);
         }))
-      r = crc.RetCode;
+      return {crc.RetCode, /*canRunAgain=*/false};
   }
 
   // Cleanup memory and reset everything back in pristine condition. This path
@@ -221,7 +221,7 @@ int main(int argc, const char **argv) {
     // Execute one iteration.
     auto r = safeLldMain(argc, argv, llvm::outs(), llvm::errs());
     if (!r.canRunAgain)
-      _exit(r.ret); // Exit now, can't re-execute again.
+      exitLld(r.ret); // Exit now, can't re-execute again.
 
     if (!mainRet) {
       mainRet = r.ret;
@@ -230,14 +230,5 @@ int main(int argc, const char **argv) {
       return r.ret;
     }
   }
-#if LLVM_ON_UNIX
-  // Re-throw the signal so it can be caught by WIFSIGNALED in
-  // llvm/lib/Support/Unix/Program.inc. This is required to correctly handle
-  // usages of `not --crash`.
-  if (*mainRet > 128) {
-    llvm::sys::unregisterHandlers();
-    raise(*mainRet - 128);
-  }
-#endif
   return *mainRet;
 }