From: Gemini Lasswell <gazally@runbox.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: 33014@debbugs.gnu.org
Subject: bug#33014: 26.1.50; 27.0.50; Fatal error after re-evaluating a thread's function
Date: Fri, 12 Oct 2018 13:02:56 -0700 [thread overview]
Message-ID: <87zhvjc4r3.fsf@runbox.com> (raw)
In-Reply-To: <83murjwplq.fsf@gnu.org> (Eli Zaretskii's message of "Fri, 12 Oct 2018 11:12:17 +0300")
Eli Zaretskii <eliz@gnu.org> writes:
> Can you please make a smaller stand-alone test case, which doesn't
> require patching Emacs? That will make it much easier to try
> reproducing the problem.
I've tried to do that without success. The bug won't reproduce if I put
all the code added to thread.el by the patch into its own file and load
it with C-u M-x byte-compile-file, and it also doesn't work to put the
resulting .elc on my load-path and load it with require.
I've determined today that having -O2 in CFLAGS is necessary to
reproduce the bug, and that -O1 or -O0 won't do it.
> Can you show the Lisp backtrace of this thread? Also, what is the
> offending object 'a' in this frame:
The Lisp backtrace is really short:
Thread 7 (Thread 0x7f1cd4dec700 (LWP 21837)):
"erb--benchmark-monitor-func" (0x158ec58)
>> #2 0x00000000006122b5 in XHASH_TABLE (a=...) at lisp.h:2241
>
> and what was its parent object in the calling frame?
Those are both optimized out with -O2. I recompiled bytecode.c with
"volatile" on the declaration of jmp_table, and got this:
(gdb) up 3
#3 exec_byte_code (bytestr=..., vector=..., maxdepth=..., args_template=...,
nargs=nargs@entry=0, args=<optimized out>,
args@entry=0x16eacf8 <bss_sbrk_buffer+9926232>) at bytecode.c:1403
1403 struct Lisp_Hash_Table *h = XHASH_TABLE (jmp_table);
(gdb) p jmp_table
$1 = make_number(514)
(gdb) p *top
$3 = XIL(0x42b4d0)
(gdb) pp *top
remove
Then I started looking at other variables in exec_byte_code, and found
this which didn't look right:
(gdb) p *vectorp
$13 = XIL(0x7f4934009523)
(gdb) pr
(((help-menu "Help" keymap (emacs-tutorial menu-item "Emacs Tutorial" help-with-tutorial :help "Lear
?\207" [yank-menu kill-ring buffer-read-only gui-backend-selection-exists-p CLIPBOARD featurep ns] 2
\205^Q^@ÅÆ!\207" [visual-line-mode word-wrap truncate-lines 0 nil toggle-truncate-lines -1] 2 nil ni
(I've truncated the result of printing *vectorp since each line is over
5000 characters long.)
Since that looked like it was unlikely to be the original value of
*vectorp, I started a new debugging session and stepped through
Thread 7's call to exec_byte_code for erb--benchmark-monitor-func, and
determined that *vectorp's initial value was erb--status-updates, which
matches the first element of the constants vector in
(symbol-function 'erb--benchmark-monitor-func).
The value of vectorp was 0x16eac38 so I set a watchpoint on
*(EMACS_INT *) 0x16eac38
and continued, and then during the execution of eval-region
it triggered here:
Thread 1 "monitor" hit Hardware watchpoint 7: *(EMACS_INT *) 0x16eac38
Old value = 60897760
New value = 24075314
setup_on_free_list (v=v@entry=0x16eac30 <bss_sbrk_buffer+9926032>,
nbytes=nbytes@entry=272) at alloc.c:3060
3060 total_free_vector_slots += nbytes / word_size;
(gdb) bt 10
#0 setup_on_free_list (v=v@entry=0x16eac30 <bss_sbrk_buffer+9926032>,
nbytes=nbytes@entry=272) at alloc.c:3060
#1 0x00000000005a9a24 in sweep_vectors () at alloc.c:3297
#2 0x00000000005adb2e in gc_sweep () at alloc.c:6872
#3 garbage_collect_1 (end=<optimized out>) at alloc.c:5860
#4 Fgarbage_collect () at alloc.c:5989
#5 0x00000000005ca478 in maybe_gc () at lisp.h:4804
#6 Ffuncall (nargs=4, args=args@entry=0x7fff210a3bc8) at eval.c:2838
#7 0x0000000000611e00 in exec_byte_code (bytestr=..., vector=..., maxdepth=...,
args_template=..., nargs=nargs@entry=2, args=<optimized out>,
args@entry=0x9bd128 <pure+781288>) at bytecode.c:632
#8 0x00000000005cdd32 in funcall_lambda (fun=XIL(0x7fff210a3bc8),
nargs=nargs@entry=2, arg_vector=0x9bd128 <pure+781288>,
arg_vector@entry=0x7fff210a3f00) at eval.c:3057
#9 0x00000000005ca54b in Ffuncall (nargs=3, args=args@entry=0x7fff210a3ef8)
at eval.c:2870
(More stack frames follow...)
Note that just as was happening when we were working through bug#32357,
the thread names which gdb prints are wrong, which I verified with:
(gdb) p current_thread
$21 = (struct thread_state *) 0xd73480 <main_thread>
(gdb) p current_thread->name
$22 = XIL(0)
Am I correct that the next step is to figure out why the garbage
collector is not marking this vector? Presumably it's no longer
attached to the function definition for erb--benchmark-monitor-func by
the time the garbage collector runs, but it's supposed to be found by
mark_stack when called from mark_one_thread for Thread 7, right?
next prev parent reply other threads:[~2018-10-12 20:02 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-11 5:30 bug#33014: 26.1.50; 27.0.50; Fatal error after re-evaluating a thread's function Gemini Lasswell
2018-10-12 8:12 ` Eli Zaretskii
2018-10-12 20:02 ` Gemini Lasswell [this message]
2018-10-13 6:23 ` Eli Zaretskii
2018-10-13 17:17 ` Gemini Lasswell
2018-10-13 18:04 ` Eli Zaretskii
2018-10-14 19:29 ` Gemini Lasswell
2018-10-15 2:37 ` Eli Zaretskii
2018-10-14 19:46 ` Andreas Schwab
2018-10-15 14:59 ` Eli Zaretskii
2018-10-15 16:22 ` Gemini Lasswell
2018-10-15 16:41 ` Eli Zaretskii
2018-10-16 18:46 ` Gemini Lasswell
2018-10-16 19:25 ` Eli Zaretskii
2018-10-16 19:38 ` Eli Zaretskii
2018-10-19 0:22 ` Gemini Lasswell
2018-10-19 8:44 ` Eli Zaretskii
2018-10-19 20:05 ` Gemini Lasswell
2018-10-20 6:41 ` Eli Zaretskii
2018-10-20 8:23 ` Andreas Schwab
2018-10-20 10:20 ` Eli Zaretskii
2018-10-20 11:30 ` Andreas Schwab
2018-10-29 18:24 ` Gemini Lasswell
2018-10-29 19:41 ` Eli Zaretskii
2018-10-19 19:32 ` Gemini Lasswell
2018-10-17 16:21 ` Eli Zaretskii
2018-10-18 1:07 ` Gemini Lasswell
2018-10-18 17:04 ` Eli Zaretskii
2018-10-19 0:39 ` Gemini Lasswell
2018-10-19 8:38 ` Eli Zaretskii
2018-10-29 18:56 ` Stefan Monnier
2018-10-31 4:49 ` Paul Eggert
2018-10-31 15:33 ` Eli Zaretskii
2018-11-01 23:15 ` Gemini Lasswell
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