Sneaky valgrind trick to detect stack memory issues.

After something is popped from a stack, we overwrite the memory
with uninitialised data (if JQ_DEBUG is on). This means that
valgrind reports use-after-pop as an uninitialised memory error.

1 files changed, 9 insertions, 0 deletions

diff --git a/jv_alloc.c b/jv_alloc.c
index 320f16e1..e127029d 100644
--- a/jv_alloc.c
+++ b/jv_alloc.c
@@ -26,3 +26,12 @@ void* jv_mem_realloc(void* p, size_t sz) {
   }
   return p;
 }
+
+#if JQ_DEBUG
+volatile char jv_mem_uninitialised;
+__attribute__((constructor)) void jv_mem_uninit_setup(){
+  char* p = malloc(1);
+  jv_mem_uninitialised = *p;
+  free(p);
+}
+#endif