bug#69263: 29.1; emacs freeze with memory swap

[Eli Zaretskii <eliz@gnu.org>]

> From: awrhygty@outlook.com
> Cc: 69263@debbugs.gnu.org
> Date: Tue, 20 Feb 2024 22:33:35 +0900
> 
> > So if you want to help us understand what happens in the strange case
> > where a Lisp program creates a 8GB Lisp string, and clear it all, on a
> > 8GB MS-Windows system, please attach GDB to Emacs after running the
> > above recipe, and produce a backtrace that can be used to try to
> > figure out what happens.  (I hope that your Emacs binary is not
> > stripped of debugging symbols, because if it's stripped, GDB will not
> > tell anything useful.)
> >
> > Thanks.
> 
> I installed MSYS2 and GDB for this.
> At first, I tried to attach with emacs PID.
> GDB says "Can't attach to process 1099".
> So I tried with WINPID.
> I am not sure it is a correct parameter.
> 
> Here is a log within MSYS2 shell:
> $ ps
>       PID    PPID    PGID     WINPID   TTY         UID    STIME COMMAND
>      1051       1    1051       3940  ?         197609 20:56:49 /usr/bin/mintty
>      1205    1052    1205       9776  pty0      197609 22:26:16 /usr/bin/ps
>      1052    1051    1052      11328  pty0      197609 20:56:49 /usr/bin/bash
>      1099    1052    1099       1384  pty0      197609 21:10:57 /c/Emacs/emacs-29.1/bin/emacs
> $ /mingw64/bin/gdb
> GNU gdb (GDB) 13.2
> Copyright (C) 2023 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 "x86_64-w64-mingw32".
> Type "show configuration" for configuration details.
> For bug reporting instructions, please see:
> <https://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".
> (gdb) attach 1384
> Attaching to process 1384
> [New Thread 1384.0xbbc]
> [New Thread 1384.0xbe0]
> [New Thread 1384.0x2bc0]
> [New Thread 1384.0x2cc4]
> [New Thread 1384.0x14a4]
> Reading symbols from C:\Emacs\emacs-29.1\bin\emacs.exe...
> (gdb) bt full
> #0  0x00007ffa73710b11 in ntdll!DbgBreakPoint () from C:\WINDOWS\SYSTEM32\ntdll.dll
> No symbol table info available.
> #1  0x00007ffa7373ca0e in ntdll!DbgUiRemoteBreakin () from C:\WINDOWS\SYSTEM32\ntdll.dll
> No symbol table info available.
> #2  0x00007ffa72237344 in KERNEL32!BaseThreadInitThunk () from C:\WINDOWS\System32\kernel32.dll
> No symbol table info available.
> #3  0x00007ffa736c26b1 in ntdll!RtlUserThreadStart () from C:\WINDOWS\SYSTEM32\ntdll.dll
> No symbol table info available.
> #4  0x0000000000000000 in ?? ()
> No symbol table info available.
> (gdb) detach
> Detaching from program: C:\Emacs\emacs-29.1\bin\emacs.exe, process 1384
> [Inferior 1 (process 1384) detached]
> (gdb) exit

This backtrace is not from an interesting thread.  You need to say
"thread 1" before "bt full", to switch to the Emacs's main
(a.k.a. "Lisp") thread.

Alternatively, say "thread apply all bt full", which will produce the
backtrace of all the threads in the program.

Thanks.