regexec.c - add assert and test for savestack overflow in Issue #20826.

We have a bug where we can overflow the save-stack. This tests for it
in a TODO test. The next patch will fix it. Note the test will only fail
in debugging as it requires the assert() to be compiled in.

1 files changed, 1 insertions, 0 deletions

diff --git a/regexec.c b/regexec.c
index c37193d004..3d9caa5104 100644
--- a/regexec.c
+++ b/regexec.c
@@ -263,6 +263,7 @@ S_regcppush(pTHX_ const regexp *rex, I32 parenfloor, U32 maxopenparen _pDEPTH)
     );
 
     SSCHECK(total_elems + REGCP_FRAME_ELEMS);
+    assert((IV)PL_savestack_max > (IV)(total_elems + REGCP_FRAME_ELEMS));
 
     /* memcpy the offs inside the stack - it's faster than for loop */
     memcpy(&PL_savestack[PL_savestack_ix], rex->offs + parenfloor + 1, paren_bytes_to_push);