Have ASAN errors show origin of memory

examples/auto-memory-safety-crash3.c

@@ -0,0 +1,32 @@
+#if 0
+/*─────────────────────────────────────────────────────────────────╗
+│ To the extent possible under law, Justine Tunney has waived      │
+│ all copyright and related or neighboring rights to this file,    │
+│ as it is written in the following disclaimers:                   │
+│   • http://unlicense.org/                                        │
+│   • http://creativecommons.org/publicdomain/zero/1.0/            │
+╚─────────────────────────────────────────────────────────────────*/
+#endif
+#include "libc/bits/bits.h"
+#include "libc/log/log.h"
+#include "libc/mem/mem.h"
+#include "libc/str/str.h"
+
+/**
+ * ASAN use-after-free memory safety crash example.
+ *
+ *     make -j8 MODE=dbg o/dbg/examples/auto-memory-safety-crash3.com
+ *     o/dbg/examples/auto-memory-safety-crash3.com
+ *
+ */
+
+int main(int argc, char *argv[]) {
+  char *buffer;
+  ShowCrashReports(); /* not needed but yoinks appropriate symbols */
+  buffer = malloc(13);
+  strcpy(buffer, "hello");
+  free(buffer);
+  asm("" : "+r"(buffer)); /* prevent compiler being smart */
+  buffer[0] = 1;
+  return 0;
+}