From 605c778e695a4535c35c5324325f310b5faf80e2 Mon Sep 17 00:00:00 2001 From: Christoph Pfister Date: Wed, 6 Jun 2007 17:17:49 +0200 Subject: [PATCH] Print backtraces in case an assert fails inside xlib/xcb. As you know there are some nasty libs / apps doing locking incorrectly. In order to improve the information given to the user when he encounters such a situation (people don't run apps in gdb normally) I created the patch attached. It's very non-intrusive (and affects only xlib/xcb, Josh told me on irc that it could be useful for other areas too, personally I don't think that it's really needed at other places ...). Some same outputs and the discussion of them: lxuser@pdln:/tmp$ ./main Got a backtrace: #0 /tmp/usr/lib/libxcb-xlib.so.0 [0xb7f9d728] #1 /tmp/usr/lib/libxcb-xlib.so.0(xcb_xlib_unlock+0x31) [0xb7f9d861] #2 ./test.so(function_a+0x11) [0xb7f9f3fd] #3 ./test.so(function_b+0x11) [0xb7f9f410] #4 ./main [0x80484a7] #5 /lib/libc.so.6(__libc_start_main+0xdc) [0xb7e60ebc] #6 ./main [0x80483f1] main: xcb_xlib.c:82: xcb_xlib_unlock: Assertion `c->xlib.lock' failed. Aborted That's kinda the normal situation. lxuser@pdln:/tmp$ ./main Got a backtrace: #0 /tmp/usr/lib/libxcb-xlib.so.0 [0xb7f90728] #1 /tmp/usr/lib/libxcb-xlib.so.0(xcb_xlib_unlock+0x31) [0xb7f90861] #2 /tmp/test.so [0xb7f923cd] #3 /tmp/test.so(function_b+0x11) [0xb7f923e0] #4 ./main [0x80484ab] #5 /lib/libc.so.6(__libc_start_main+0xdc) [0xb7e53ebc] #6 ./main [0x80483f1] main: xcb_xlib.c:82: xcb_xlib_unlock: Assertion `c->xlib.lock' failed. Aborted There are two possible reasons that the name doesn't appear in #2: a) a hidden symbol or a symbol with statical linkage in a library b) a symbol in an app not compiled with -rdynamic. But in both cases you still know _where_ the caller is. Note that in this example test.so was compiled with -fomit-frame-pointer; this isn't an issue as _one_ (= the caller) stack trace is still valid (as long as you don't have the insane idea to compile xcb with -fo-f-p). Another issue that may appear is "tail call elimination" (some entries are mysteriously missing; this is quite ugly, but you still get enough information so that you can do something useful with the issue e.g. by disassembling the relevant parts with gdb). Signed-off-by: Jamey Sharp --- configure.ac | 2 ++ src/xcb_xlib.c | 38 +++++++++++++++++++++++++++++++++++--- 2 files changed, 37 insertions(+), 3 deletions(-) diff --git a/configure.ac b/configure.ac index d73e51f..b446e7f 100644 --- a/configure.ac +++ b/configure.ac @@ -48,6 +48,8 @@ PKG_CHECK_MODULES(XDMCP, xdmcp, ], [$XDMCP_LIBS]), [AC_MSG_RESULT(no)]) +AC_CHECK_HEADER([execinfo.h], [AC_DEFINE(HAVE_BACKTRACE,1,[Has backtrace*() needed for retrieving stack traces])]) + AC_SUBST(NEEDED) # Find the xcb-proto protocol descriptions diff --git a/src/xcb_xlib.c b/src/xcb_xlib.c index 59f972c..07d530c 100644 --- a/src/xcb_xlib.c +++ b/src/xcb_xlib.c @@ -28,6 +28,38 @@ #include +#ifdef HAVE_BACKTRACE +#include +#include +#include +#endif + +static void xcb_xlib_printbt(void) +{ +#ifdef HAVE_BACKTRACE + void *array[20]; + int size; + char **strings; + int i; + + size = backtrace(array, 20); + strings = backtrace_symbols(array, size); + + printf("Got a backtrace:\n"); + + for (i = 0; i < size; ++i) + printf("#%i %s\n", i, strings[i]); + + free(strings); +#endif +} + +#ifndef NDEBUG +#define xcb_assert(x) do { if (!(x)) { xcb_xlib_printbt(); assert(x); } } while(0) +#else +#define xcb_assert(x) +#endif + unsigned int xcb_get_request_sent(xcb_connection_t *c) { if(c->has_error) @@ -38,7 +70,7 @@ unsigned int xcb_get_request_sent(xcb_connection_t *c) void xcb_xlib_lock(xcb_connection_t *c) { _xcb_lock_io(c); - assert(!c->xlib.lock); + xcb_assert(!c->xlib.lock); c->xlib.lock = 1; c->xlib.thread = pthread_self(); _xcb_unlock_io(c); @@ -47,8 +79,8 @@ void xcb_xlib_lock(xcb_connection_t *c) void xcb_xlib_unlock(xcb_connection_t *c) { _xcb_lock_io(c); - assert(c->xlib.lock); - assert(pthread_equal(c->xlib.thread, pthread_self())); + xcb_assert(c->xlib.lock); + xcb_assert(pthread_equal(c->xlib.thread, pthread_self())); c->xlib.lock = 0; pthread_cond_broadcast(&c->xlib.cond); _xcb_unlock_io(c); -- 2.7.4