[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, 8 insertions, 2 deletions

diff --git a/llvm/lib/Support/Process.cpp b/llvm/lib/Support/Process.cpp
index 9f0b689..8626117 100644
--- a/llvm/lib/Support/Process.cpp
+++ b/llvm/lib/Support/Process.cpp
@@ -20,6 +20,8 @@
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Program.h"
 
+#include <stddef.h> // for _Exit
+
 using namespace llvm;
 using namespace sys;
 
@@ -91,10 +93,14 @@ static bool coreFilesPrevented = !LLVM_ENABLE_CRASH_DUMPS;
 bool Process::AreCoreFilesPrevented() { return coreFilesPrevented; }
 
 LLVM_ATTRIBUTE_NORETURN
-void Process::Exit(int RetCode) {
+void Process::Exit(int RetCode, bool NoCleanup) {
   if (CrashRecoveryContext *CRC = CrashRecoveryContext::GetCurrent())
     CRC->HandleExit(RetCode);
-  ::exit(RetCode);
+
+  if (NoCleanup)
+    _Exit(RetCode);
+  else
+    ::exit(RetCode);
 }
 
 // Include the platform-specific parts of this class.