From: Willy Tarreau <w@1wt.eu>
Date: Fri, 22 Jan 2021 13:15:46 +0000 (+0100)
Subject: MEDIUM: debug: now always print a backtrace on CRASH_NOW() and friends
X-Git-Tag: v2.4-dev6~5
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=5baf4fe31ad2a5b1e0402c0a6d580dda203a2dab;p=thirdparty%2Fhaproxy.git

MEDIUM: debug: now always print a backtrace on CRASH_NOW() and friends

The purpose is to enable the dumping of a backtrace on BUG_ON(). While
it's very useful to know that a condition was met, very often some
caller context is missing to figure how the condition could happen.
From now on, on systems featuring backtrace, a backtrace of the calling
thread will also be dumped to stderr in addition to the unexpected
condition. This will help users of DEBUG_STRICT as they'll most often
find this backtrace in their logs even if they can't find their core
file.

A new "debug dev bug" expert-mode CLI command was added to test the
feature.
---

diff --git a/include/haproxy/bug.h b/include/haproxy/bug.h
index f5ed7f419a..a2cf6ba0b8 100644
--- a/include/haproxy/bug.h
+++ b/include/haproxy/bug.h
@@ -39,12 +39,12 @@
 
 #ifdef DEBUG_USE_ABORT
 /* abort() is better recognized by code analysis tools */
-#define ABORT_NOW() abort()
+#define ABORT_NOW() do { extern void ha_backtrace_to_stderr(); ha_backtrace_to_stderr(); abort(); } while (0)
 #else
 /* More efficient than abort() because it does not mangle the
   * stack and stops at the exact location we need.
   */
-#define ABORT_NOW() (*(volatile int*)1=0)
+#define ABORT_NOW() do { extern void ha_backtrace_to_stderr(); ha_backtrace_to_stderr(); (*(volatile int*)1=0); } while (0)
 #endif
 
 /* BUG_ON: complains if <cond> is true when DEBUG_STRICT or DEBUG_STRICT_NOCRASH
@@ -55,7 +55,7 @@
 #if defined(DEBUG_STRICT)
 #define CRASH_NOW() ABORT_NOW()
 #else
-#define CRASH_NOW()
+#define CRASH_NOW() do { ha_backtrace_to_stderr(); } while (0)
 #endif
 
 #define BUG_ON(cond) _BUG_ON(cond, __FILE__, __LINE__)
diff --git a/src/debug.c b/src/debug.c
index 2a5e164c6d..7d73fdc9e0 100644
--- a/src/debug.c
+++ b/src/debug.c
@@ -322,6 +322,19 @@ static int debug_parse_cli_exit(char **args, char *payload, struct appctx *appct
 	return 1;
 }
 
+/* parse a "debug dev bug" command. It always returns 1, though it should never return.
+ * Note: we make sure not to make the function static so that it appears in the trace.
+ */
+int debug_parse_cli_bug(char **args, char *payload, struct appctx *appctx, void *private)
+{
+	if (!cli_has_level(appctx, ACCESS_LVL_ADMIN))
+		return 1;
+
+	_HA_ATOMIC_ADD(&debug_commands_issued, 1);
+	BUG_ON(one > zero);
+	return 1;
+}
+
 /* parse a "debug dev close" command. It always returns 1. */
 static int debug_parse_cli_close(char **args, char *payload, struct appctx *appctx, void *private)
 {
@@ -1144,6 +1157,7 @@ REGISTER_PER_THREAD_INIT(init_debug_per_thread);
 
 /* register cli keywords */
 static struct cli_kw_list cli_kws = {{ },{
+	{{ "debug", "dev", "bug", NULL },   "debug dev bug               : call BUG_ON()",                   debug_parse_cli_bug,   NULL, NULL, NULL, ACCESS_EXPERT },
 	{{ "debug", "dev", "close", NULL }, "debug dev close <fd>        : close this file descriptor",      debug_parse_cli_close, NULL, NULL, NULL, ACCESS_EXPERT },
 	{{ "debug", "dev", "delay", NULL }, "debug dev delay [ms]        : sleep this long",                 debug_parse_cli_delay, NULL, NULL, NULL, ACCESS_EXPERT },
 #if defined(DEBUG_DEV)