[lld] Force crashes when env var LLD_FORCE_CRASH set

[abrachet]

Summary

This will be used to test clang driver lld crash reproduction

[MaskRay]

Personally I am not feeling very comfortable adding such an environment variable just so that it can be tested.
I think it may make sense to add the clang driver change without a test.

[aganea]

In D121724#3384642, @MaskRay wrote:

Personally I am not feeling very comfortable adding such an environment variable just so that it can be tested.
I think it may make sense to add the clang driver change without a test.

We could also use LLD_IN_TEST=-1 as a signal for artificially testing the crash? Clang has #pragma clang __debug crash. I don't think crafting an invalid .o is reasonable to me, since we want to survive invalid inputs at all times.

lld/Common/ErrorHandler.cpp

113

I think you should use LLVM_BUILTIN_TRAP since __builtin_trap() isn't supported by all compilers.

114

Add extra LF please.

lld/tools/lld/lld.cpp

244

Can this go above L217? Do we need to have the __buildin_trap at two places? Here an in exitLld()?

[abrachet]

No longer needed for D120175

lld/Common/ErrorHandler.cpp

void lld::exitLld(int val) {
   // Ensures that the thread pool for the parallel algorithms is stopped to
   // avoid intermittent crashes on Windows when exiting.
   if (!CrashRecoveryContext::GetCurrent())
     llvm_shutdown();
 
   if (hasContext())
     lld::errorHandler().flushStreams();
 
+  if (::getenv("LLD_FORCE_CRASH"))
+    __builtin_trap();
   // When running inside safeLldMain(), restore the control flow back to the
   // CrashRecoveryContext. Otherwise simply use _exit(), meanning no cleanup,
   // since we want to avoid further crashes on shutdown.
   llvm::sys::Process::Exit(val, /*NoCleanup=*/true);
 }
 
 void lld::diagnosticHandler(const DiagnosticInfo &di) {
   SmallString<128> s;
   raw_svector_ostream os(s);

lld/test/ELF/force-crash.s

+RUN: not ld.lld 2>&1 | FileCheck %s
+CHECK: error: no input files
+CHECK-NOT: PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
+
+RUN: LLD_FORCE_CRASH=1 not --crash ld.lld 2>&1 | FileCheck %s --check-prefix=CRASH
+CRASH: error: no input files
+CRASH: PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.

lld/tools/lld/lld.cpp

static unsigned inTestVerbosity() {
   StringRef(getenv("LLD_IN_TEST")).getAsInteger(10, v);
   return v;
 }
 
 int main(int argc, const char **argv) {
   InitLLVM x(argc, argv);
   sys::Process::UseANSIEscapeCodes(true);
 
+  int ret = [argc, argv] {
     // Not running in lit tests, just take the shortest codepath with global
     // exception handling and no memory cleanup on exit.
     if (!inTestVerbosity())
       return lldMain(argc, argv, llvm::outs(), llvm::errs());
 
     Optional<int> mainRet;
     CrashRecoveryContext::Enable();
 
     for (unsigned i = inTestVerbosity(); i > 0; --i) {
       // Disable stdout/stderr for all iterations but the last one.
       inTestOutputDisabled = (i != 1);
 
       // Execute one iteration.
       auto r = safeLldMain(argc, argv, llvm::outs(), llvm::errs());
       if (!r.canRunAgain)
         exitLld(r.ret); // Exit now, can't re-execute again.
 
       if (!mainRet) {
         mainRet = r.ret;
       } else if (r.ret != *mainRet) {
         // Exit now, to fail the tests if the result is different between runs.
         return r.ret;
       }
     }
     return *mainRet;
+  }();
+  if (::getenv("LLD_FORCE_CRASH"))
+    __builtin_trap();
+  return ret;
 }