[Support] Don't modify the current EH context during stack unwinding

Copy it instead. Otherwise, key registers (such as RBP) may get zeroed
out by the stack unwinder.

Fixes CrashRecoveryTest.DumpStackCleanup with MSVC in release builds.

Reviewed By: stella.stamenova

Differential Revision: https://reviews.llvm.org/D73809

diff --git a/llvm/lib/Support/Windows/Signals.inc b/llvm/lib/Support/Windows/Signals.inc
index a5c833d..e5f36bc 100644 (file)
--- a/llvm/lib/Support/Windows/Signals.inc
+++ b/llvm/lib/Support/Windows/Signals.inc
@@ -820,7 +820,13 @@ static LONG WINAPI LLVMUnhandledExceptionFilter(LPEXCEPTION_POINTERS ep) {
                    << "\n";
   }
 
-  LocalPrintStackTrace(llvm::errs(), ep ? ep->ContextRecord : nullptr);
+  // Stack unwinding appears to modify the context. Copy it to preserve the
+  // caller's context.
+  CONTEXT ContextCopy;
+  if (ep)
+    memcpy(&ContextCopy, ep->ContextRecord, sizeof(ContextCopy));
+
+  LocalPrintStackTrace(llvm::errs(), ep ? &ContextCopy : nullptr);
 
   return EXCEPTION_EXECUTE_HANDLER;
 }