Have ASAN errors show origin of memory

examples/auto-memory-safety-crash2.c

@@ -0,0 +1,65 @@
+#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 heap memory safety crash example.
+ *
+ *     make -j8 MODE=dbg o/dbg/examples/auto-memory-safety-crash2.com
+ *     o/dbg/examples/auto-memory-safety-crash2.com
+ *
+ * You should see:
+ *
+ *     heap overrun 1-byte store at 0x10008004002d shadow 0x20090000005
+ *     ./o/dbg/examples/auto-memory-safety-crash2.com
+ *                                             x
+ *     OOOOOOOOOOOUUUUUUUUUUUUUUUU.............OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
+ *        |-7     |-6     |-6     |0      |5      |-7     |-7     |-7     |-7
+ *        »!@     ÿ▄:Y╩≥= S       hello ∙∙∙∙∙∙∙           ♪     GT◘&@     á+@     »!@  
+ *     000000400000-00000042b000 .text
+ *     00000042b000-00000042d000 .data
+ *     00007fff0000-00008000ffff
+ *     000080070000-00008008ffff
+ *     02008fff0000-02009000ffff ←shadow
+ *     0e007fff0000-0e008000ffff
+ *     10003ab90000-10003abaffff
+ *     100080000000-10008000ffff ←address
+ *     6ffffffe0000-6fffffffffff
+ *
+ *     the memory was allocated by
+ *     0x100080040020 64 bytes [dlmalloc]
+ *     0x100080040030 13 bytes [actual]
+ *           402608 main
+ *           402ba0 cosmo
+ *           4021af _start
+ *
+ *     the crash was caused by
+ *     0x0000000000404793: __die at libc/log/die.c:40
+ *     0x0000000000404f56: __asan_report_store at libc/intrin/asan.c:1183
+ *     0x0000000000402579: main at examples/auto-memory-safety-crash2.c:30
+ *     0x000000000040270f: cosmo at libc/runtime/cosmo.S:64
+ *     0x00000000004021ae: _start at libc/crt/crt.S:77
+ *
+ */
+
+int main(int argc, char *argv[]) {
+  char *buffer;
+  ShowCrashReports(); /* not needed but yoinks appropriate symbols */
+  buffer = malloc(13);
+  strcpy(buffer, "hello");
+  int i = 13;
+  asm("" : "+r"(i)); /* prevent compiler being smart */
+  buffer[i] = 1;
+  asm("" : "+r"(buffer)); /* prevent compiler being smart */
+  return 0;
+}