# Set\_breakpoint crash **URL:** \ **Category:** Help!\ **Created:** [December 23, 2021, 2:40am UTC](https://swi-prolog.discourse.group/t/set-breakpoint-crash/4800 "2021-12-23T02:40:48Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![swi](https://avatars.discourse-cdn.com/v4/letter/s/51bf81/32.png) [@swi](https://swi-prolog.discourse.group/u/swi)\ **Post date:** [December 23, 2021, 2:40am UTC](https://swi-prolog.discourse.group/t/set-breakpoint-crash/4800/1 "2021-12-23T02:40:48Z")
```prolog sb(PI,Line,Id) :- % get src file pi_head(PI,Head), clause(Head,_,Ref), clause_property(Ref,file(File)), % set breakpoint set_breakpoint(File,Line,1,Id). 8 ?- sb(mod:somepred/1,1229,I). [...]received fatal signal 11 (segv) C-stack trace labeled "crash": [0] save_backtrace() at :? [0x7f03031884f1] [1] print_c_backtrace() at :? [0x7f03031885ad] [2] sigCrashHandler() at :? [0x7f03031886bd] [3] __restore_rt() at sigaction.c:? [0x7f0302f3cda0] [4] pl_clause_from_source4_va() at pl-srcfile.c:? [0x7f03031499ca] [5] PL_next_solution___LD() at :? [0x7f0303191c02] [6] query_loop() at :? [0x7f03031d3d88] [7] prologToplevel() at :? [0x7f03031d3c1b] [8] PL_toplevel() at ??:? [0x7f03031e89eb] [9] swipl(+0x10b1) [0x55dfe77370b1] [10] __libc_start_main() at ??:? [0x7f0302f27b25] [11] swipl(+0x10ee) [0x55dfe77370ee] Prolog stack: [13] system:$clause_from_source/4 [PC=1 in supervisor] [12] prolog_breakpoints:set_breakpoint/5 [PC=25 in clause 1] [10] sb/3 [PC=30 in clause 1] [9] $toplevel:toplevel_call/1 [PC=3 in clause 1] [8] $toplevel:stop_backtrace/2 [PC=4 in clause 1] [7] $tabling:$wfs_call/2 [PC=17 in clause 1] [5] $toplevel:$execute_goal2/3 [PC=31 in clause 1] [3] $toplevel:$query_loop/0 [PC=39 in clause 2] [2] $toplevel:$runtoplevel/0 [PC=19 in clause 1] [1] $toplevel:$toplevel/0 [PC=3 in clause 1] [0] system:$c_call_prolog/0 [PC=0 in top query clause] Running on_halt hooks with status 139 Killing 1530697 with default signal handlers ``` I am getting a crash when trying to set a breakpoint; this happens with the graphical debugger also; it happens with one prolog source code file, unfortunately I can’t reproduce it with a smaller file, but hopefully the above gives enough information to track down the problem. Running the latest SWI-Prolog (8.5.4-13-g9d2babb2c). ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [December 23, 2021, 7:54am UTC](https://swi-prolog.discourse.group/t/set-breakpoint-crash/4800/2 "2021-12-23T07:54:17Z")
No clue. I guess the best is to recompile for debugging. The should get us line numbers. Maybe that is enough. Otherwise we’ll need a debugger … ---
**Author:** ![swi](https://avatars.discourse-cdn.com/v4/letter/s/51bf81/32.png) [@swi](https://swi-prolog.discourse.group/u/swi)\ **Post date:** [December 23, 2021, 7:18pm UTC](https://swi-prolog.discourse.group/t/set-breakpoint-crash/4800/3 "2021-12-23T19:18:13Z")
Here is the crash with line numbers ```prolog C-stack trace labeled "crash": [0] save_backtrace() at /tmp/swipl-devel/src/os/pl-cstack.c:331 [0x7f1362ecc74b] [1] print_c_backtrace() at /tmp/swipl-devel/src/os/pl-cstack.c:868 [0x7f1362eccfe3] [2] sigCrashHandler() at /tmp/swipl-devel/src/os/pl-cstack.c:908 [0x7f1362ecd15d] [3] alt_segv_handler() at /tmp/swipl-devel/src/pl-setup.c:753 [0x7f1362dcefe8] [4] __restore_rt() at sigaction.c:? [0x7f1362b28da0] [5] pl_clause_from_source4_va() at /tmp/swipl-devel/src/pl-srcfile.c:1819 [0x7f1362e14659] [6] PL_next_solution___LD() at /tmp/swipl-devel/src/pl-vmi.c:4585 [0x7f1362d05c9c] [7] query_loop() at /tmp/swipl-devel/src/pl-pro.c:147 [0x7f1362d9918e] [8] prologToplevel() at /tmp/swipl-devel/src/pl-pro.c:496 [0x7f1362d99e36] [9] PL_toplevel() at /tmp/swipl-devel/src/pl-fli.c:4558 [0x7f1362e9295a] [10] swipl(+0x11b9) [0x555f0f34d1b9] [11] __libc_start_main() at ??:? [0x7f1362b13b25] [12] swipl(+0x109e) [0x555f0f34d09e] Prolog stack: [14] system:$clause_from_source/4 [PC=1 in supervisor] [13] prolog_breakpoints:set_breakpoint/5 [PC=25 in clause 1] [11] sb/3 [PC=30 in clause 1] [10] system:/1 [PC=8 in clause -1] [9] $toplevel:toplevel_call/1 [PC=3 in clause 1] [8] $toplevel:stop_backtrace/2 [PC=4 in clause 1] [7] $tabling:$wfs_call/2 [PC=17 in clause 1] [5] $toplevel:$execute_goal2/3 [PC=31 in clause 1] [3] $toplevel:$query_loop/0 [PC=39 in clause 2] [2] $toplevel:$runtoplevel/0 [PC=19 in clause 1] [1] $toplevel:$toplevel/0 [PC=3 in clause 1] [0] system:$c_call_prolog/0 [PC=0 in top query clause] ``` Seems like the problem is in `pl_clause_from_source4_va() at /tmp/swipl-devel/src/pl-srcfile.c:1819 [0x7f1362e14659]` EDIT: in gdb `cl` is null which is causing the segfault. No idea why it is null though. ```prolog │ 1818 │ │ > 1819 if ( cl->source_no == source_no ) │ │ 1820 { if ( ln >= (int)cl->line_no ) │ │ 1821 { if ( !c || c->line_no < cl->line_no ) [...] Thread 1 "swipl" received signal SIGSEGV, Segmentation fault. 0x00007ffff7c5a659 in pl_clause_from_source4_va (PL __t0=231, PL__ ac=4, PL__ctx=0x7fffffffd2a0) at /tmp/swipl-devel/src/pl-srcfile.c:1819 (gdb) print cl $1 = (Clause) 0x0 (gdb) ``` ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [December 24, 2021, 5:05pm UTC](https://swi-prolog.discourse.group/t/set-breakpoint-crash/4800/4 "2021-12-24T17:05:14Z")
> [@swi](#): > > No idea why it is null though. That should not be possible ☹ So, most likely something more fundamental is wrong. Any way to reproduce this? ---
**Author:** ![swi](https://avatars.discourse-cdn.com/v4/letter/s/51bf81/32.png) [@swi](https://swi-prolog.discourse.group/u/swi)\ **Post date:** [December 24, 2021, 5:47pm UTC](https://swi-prolog.discourse.group/t/set-breakpoint-crash/4800/5 "2021-12-24T17:47:26Z")
> [@jan](#): > > Any way to reproduce this? I tried to make a small reproducible version but it didn’t reproduce with the smaller source. I will try to bisect the code and see if I can make it reproducible with a small sample. It will most likely be some days. ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [December 25, 2021, 11:04am UTC](https://swi-prolog.discourse.group/t/set-breakpoint-crash/4800/7 "2021-12-25T11:04:27Z")
It doesn’t need to be small. The way to find this is first to try enabling addresssanitizer (see CMAKE.md) and see whether we have to do with memory corruption. If not, I typically add a little C function that checks for the error condition and insert that at some places in the source to find where the issue is introduced. Can be tedious ☹ ---
**Author:** ![swi](https://avatars.discourse-cdn.com/v4/letter/s/51bf81/32.png) [@swi](https://swi-prolog.discourse.group/u/swi)\ **Post date:** [December 25, 2021, 4:25pm UTC](https://swi-prolog.discourse.group/t/set-breakpoint-crash/4800/8 "2021-12-25T16:25:16Z")
I’ll report when I have found some more info. Merry Christmas, and have a good time of rest! ---
**Author:** ![swi](https://avatars.discourse-cdn.com/v4/letter/s/51bf81/32.png) [@swi](https://swi-prolog.discourse.group/u/swi)\ **Post date:** [December 26, 2021, 8:41pm UTC](https://swi-prolog.discourse.group/t/set-breakpoint-crash/4800/9 "2021-12-26T20:41:53Z")
Found some more information about this bug. In the original prolog source I have a few predicates that are dynamic/1 _and_ thread\_local/1: - If I **comment out** the thread\_local/1 declaration and leave the predicates as dynamic/1 the bug disappears. - I tried to reduce it to a smaller piece of prolog source (with thread\_local/1 declarations) but still could not make a small reproducible sample. - I’ll keep trying to make a reproducible version. ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [December 27, 2021, 8:53am UTC](https://swi-prolog.discourse.group/t/set-breakpoint-crash/4800/10 "2021-12-27T08:53:41Z")
That rings a bell. Note that thread\_local always implies dynamic. Pushed a fix. Can’t verify it fixes the crash, but it was surely wrong code and could explain a crash. ---
**Author:** ![swi](https://avatars.discourse-cdn.com/v4/letter/s/51bf81/32.png) [@swi](https://swi-prolog.discourse.group/u/swi)\ **Post date:** [December 27, 2021, 10:35am UTC](https://swi-prolog.discourse.group/t/set-breakpoint-crash/4800/11 "2021-12-27T10:35:16Z")
> [@jan](#): > > Can’t verify it fixes the crash, but it was surely wrong code and could explain a crash. Certainly! The patch fixes it, thanks!