Re: recent master core dumps building on FreeBSD i386

[Joseph Mingrone <jrm@ftfl.ca>]

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Paul Eggert <eggert@cs.ucla.edu> writes:

> On 10/18/18 9:02 AM, Eli Zaretskii wrote:
>> Can you please repeat this experiment, and then, when it crashes, do
>> this:

>>    (gdb) source ./.gdbinit
>>    (gdb) frame 2
>>    (gdb) p/x a
>>    (gdb) xtype

>> and show us the results?

> Also, please try these GDB commands when debugging ./temacs:

> b syms_of_threads
> r -Q
> p &main_thread
> disas syms_of_threads
> p &Vmain_thread

> I'm attaching the output of these commands on Fedora 28 x86-64 compiled with 'gcc -m32 -march=native -g3 -O2' (AMD Phenom II X4 910e). Evidently your compiler (clang?) is not inlining make_lisp_ptr, but
> it's still useful to know what it's up to. I see that GCC optimizes away not only the call to make_lisp_ptr, but also the runtime check 'TAGGEDP (a, type) && XUNTAG (a, type, char) == ptr', I guess because
> GCC knows that main_thread is properly aligned so TAGGEDP must succeed here. clang isn't smart enough to do this sort of optimization (at least on Fedora) so if you're using clang that might partly explain
> the problem.

root@11i386-default:/wrkdirs/usr/ports/editors/emacs-devel/work-full/emacs-e511b9d/src # /usr/local/bin/gdb ./temacs
GNU gdb (GDB) 8.2 [GDB v8.2 for FreeBSD]
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "i386-portbld-freebsd11.2".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./temacs...done.
SIGINT is used by the debugger.
Are you sure you want to change it? (y or n) [answered Y; input not from terminal]
Environment variable "DISPLAY" not defined.
TERM = screen-256color
Breakpoint 1 at 0x81599de: file emacs.c, line 370.
Temporary breakpoint 2 at 0x8177f95: file sysdep.c, line 1080.
(gdb) b syms_of_threads
Breakpoint 3 at 0x8249851: file thread.c, line 1098.
(gdb) r -Q
Starting program: /wrkdirs/usr/ports/editors/emacs-devel/work-full/emacs-e511b9d/src/temacs -Q

Breakpoint 3, syms_of_threads () at thread.c:1098
1098          defsubr (&Smake_thread);
(gdb) p &main_thread
$1 = (struct thread_state *) 0x8554d0c <main_thread>
(gdb) disas syms_of_threads
Dump of assembler code for function syms_of_threads:
   0x08249840 <+0>:     push   %ebp
   0x08249841 <+1>:     mov    %esp,%ebp
   0x08249843 <+3>:     push   %esi
   0x08249844 <+4>:     push   $0x8506838
   0x08249849 <+9>:     call   0x8202e90 <defsubr>
   0x0824984e <+14>:    add    $0x4,%esp
=> 0x08249851 <+17>:    push   $0x8506898
   0x08249856 <+22>:    call   0x8202e90 <defsubr>
   0x0824985b <+27>:    add    $0x4,%esp
   0x0824985e <+30>:    push   $0x8506858
   0x08249863 <+35>:    call   0x8202e90 <defsubr>
   0x08249868 <+40>:    add    $0x4,%esp
   0x0824986b <+43>:    push   $0x85068b8
   0x08249870 <+48>:    call   0x8202e90 <defsubr>
   0x08249875 <+53>:    add    $0x4,%esp
   0x08249878 <+56>:    push   $0x85068d8
   0x0824987d <+61>:    call   0x8202e90 <defsubr>
   0x08249882 <+66>:    add    $0x4,%esp
   0x08249885 <+69>:    push   $0x85068f8
   0x0824988a <+74>:    call   0x8202e90 <defsubr>
   0x0824988f <+79>:    add    $0x4,%esp
   0x08249892 <+82>:    push   $0x8506918
   0x08249897 <+87>:    call   0x8202e90 <defsubr>
   0x0824989c <+92>:    add    $0x4,%esp
   0x0824989f <+95>:    push   $0x8506938
   0x082498a4 <+100>:   call   0x8202e90 <defsubr>
   0x082498a9 <+105>:   add    $0x4,%esp
   0x082498ac <+108>:   push   $0x8506878
   0x082498b1 <+113>:   call   0x8202e90 <defsubr>
   0x082498b6 <+118>:   add    $0x4,%esp
   0x082498b9 <+121>:   push   $0x8506958
   0x082498be <+126>:   call   0x8202e90 <defsubr>
   0x082498c3 <+131>:   add    $0x4,%esp
   0x082498c6 <+134>:   push   $0x8506978
   0x082498cb <+139>:   call   0x8202e90 <defsubr>
   0x082498d0 <+144>:   add    $0x4,%esp
   0x082498d3 <+147>:   push   $0x8506998
   0x082498d8 <+152>:   call   0x8202e90 <defsubr>
   0x082498dd <+157>:   add    $0x4,%esp
--Type <RET> for more, q to quit, c to continue without paging--
   0x082498e0 <+160>:   push   $0x85069b8
   0x082498e5 <+165>:   call   0x8202e90 <defsubr>
   0x082498ea <+170>:   add    $0x4,%esp
   0x082498ed <+173>:   push   $0x85069d8
   0x082498f2 <+178>:   call   0x8202e90 <defsubr>
   0x082498f7 <+183>:   add    $0x4,%esp
   0x082498fa <+186>:   push   $0x85069f8
   0x082498ff <+191>:   call   0x8202e90 <defsubr>
   0x08249904 <+196>:   add    $0x4,%esp
   0x08249907 <+199>:   push   $0x8506a18
   0x0824990c <+204>:   call   0x8202e90 <defsubr>
   0x08249911 <+209>:   add    $0x4,%esp
   0x08249914 <+212>:   push   $0x8506a38
   0x08249919 <+217>:   call   0x8202e90 <defsubr>
   0x0824991e <+222>:   add    $0x4,%esp
   0x08249921 <+225>:   push   $0x8506a58
   0x08249926 <+230>:   call   0x8202e90 <defsubr>
   0x0824992b <+235>:   add    $0x4,%esp
   0x0824992e <+238>:   push   $0x8506a78
   0x08249933 <+243>:   call   0x8202e90 <defsubr>
   0x08249938 <+248>:   add    $0x4,%esp
   0x0824993b <+251>:   push   $0x8554dc0
   0x08249940 <+256>:   call   0x81bad60 <staticpro>
   0x08249945 <+261>:   add    $0x4,%esp
   0x08249948 <+264>:   movl   $0x0,0x8554dc0
   0x08249952 <+274>:   push   $0xe
   0x08249954 <+276>:   push   $0x82ab272
   0x08249959 <+281>:   call   0x8202460 <intern_c_string_1>
   0x0824995e <+286>:   add    $0x8,%esp
   0x08249961 <+289>:   mov    %eax,%esi
   0x08249963 <+291>:   push   $0xd
   0x08249965 <+293>:   push   $0x82ab281
   0x0824996a <+298>:   call   0x8202460 <intern_c_string_1>
   0x0824996f <+303>:   add    $0x8,%esp
   0x08249972 <+306>:   push   $0x0
   0x08249974 <+308>:   push   %eax
   0x08249975 <+309>:   push   %esi
   0x08249976 <+310>:   call   0x81c0930 <Fdefalias>
   0x0824997b <+315>:   add    $0xc,%esp
   0x0824997e <+318>:   push   $0x7
--Type <RET> for more, q to quit, c to continue without paging--
   0x08249980 <+320>:   push   $0x82ab691
   0x08249985 <+325>:   call   0x8202460 <intern_c_string_1>
   0x0824998a <+330>:   add    $0x8,%esp
   0x0824998d <+333>:   push   $0x0
   0x0824998f <+335>:   push   %eax
   0x08249990 <+336>:   call   0x81e4ad0 <Fprovide>
   0x08249995 <+341>:   add    $0x8,%esp
   0x08249998 <+344>:   push   $0x8557a54
   0x0824999d <+349>:   push   $0x82ab28f
   0x082499a2 <+354>:   push   $0x8554dc8
   0x082499a7 <+359>:   call   0x82030f0 <defvar_lisp>
   0x082499ac <+364>:   add    $0xc,%esp
   0x082499af <+367>:   cmpb   $0x0,0x8557ef0
   0x082499b6 <+374>:   je     0x82499c4 <syms_of_threads+388>
   0x082499b8 <+376>:   movl   $0x8554d11,0x8557a54
   0x082499c2 <+386>:   jmp    0x82499e9 <syms_of_threads+425>
   0x082499c4 <+388>:   mov    $0x8554d14,%eax
   0x082499c9 <+393>:   test   $0x7,%al
   0x082499cb <+395>:   jne    0x82499ec <syms_of_threads+428>
   0x082499cd <+397>:   movl   $0x8554d11,0x8557a54
   0x082499d7 <+407>:   mov    $0x7f000000,%eax
   0x082499dc <+412>:   and    0x8554d0c,%eax
   0x082499e2 <+418>:   cmp    $0x54000000,%eax
   0x082499e7 <+423>:   jne    0x8249a00 <syms_of_threads+448>
   0x082499e9 <+425>:   pop    %esi
   0x082499ea <+426>:   pop    %ebp
   0x082499eb <+427>:   ret
   0x082499ec <+428>:   push   $0x492
   0x082499f1 <+433>:   push   $0x828071a
   0x082499f6 <+438>:   push   $0x8280b68
   0x082499fb <+443>:   call   0x81b6b50 <die>
   0x08249a00 <+448>:   push   $0x46d
   0x08249a05 <+453>:   push   $0x82ab73e
   0x08249a0a <+458>:   push   $0x82ab29b
   0x08249a0f <+463>:   call   0x81b6b50 <die>
End of assembler dump.
(gdb) p &Vmain_thread
No symbol "Vmain_thread" in current context.
(gdb) quit
A debugging session is active.

        Inferior 1 [process 86154] will be killed.

Quit anyway? (y or n) y

root@11i386-default:/wrkdirs/usr/ports/editors/emacs-devel/work-full/emacs-e511b9d/src # CC --version
FreeBSD clang version 6.0.0 (tags/RELEASE_600/final 326565) (based on LLVM 6.0.0)
Target: i386-unknown-freebsd11.2
Thread model: posix
InstalledDir: /usr/bin

> Also, please investigate what the macro GCALIGNED_STRUCT expands to. You can use 'gcc -E' to do that.

I'll get back to you with this soon.

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