Re: [MPS-test] scratch/igc branch (commit: 42731228d24) crashed

[Pip Cet <pipcet@protonmail.com>]

"Eval Exec" <execvy@gmail.com> writes:

> I wanted to help test the scratch/igc branch, so I compiled it from
> commit 42731228d24.

Thank you for doing that!

> Then I build it by
> ```bash
> make extraclean
> ./autogen.sh \
>   && ./configure \
>   --prefix=$(realpath ../emacs-build)\
>   --with-mps \
>   --with-imagemagick \
>   --with-modules --with-x-toolkit=lucid --without-compress-install \
>   --without-toolkit-scroll-bars --with-native-compilation  --with-mailutils\
>   --with-tree-sitter --with-xinput2  \
>   --with-dbus  --with-native-compilation=aot \
>   --with-file-notification=inotify\
>   && make -j20 install

Like Eli, I'm suspecting the Lucid widget code...

> It works perfectly for the first hour, but then it crashes, and I
> don't know how to reproduce the issue.
>
> I think the crash is caused by "window size adjustments"
> ```
> (gdb) bt
> #0  0x00007f47afea2efc in __pthread_kill_implementation () from
> /nix/store/dbcw19dshdwnxdv5q2g6wldj6syyvq7l-glibc-2.39-52/lib/libc.so.6
> #1  0x00007f47afe52e86 in raise () from
> /nix/store/dbcw19dshdwnxdv5q2g6wldj6syyvq7l-glibc-2.39-52/lib/libc.so.6
> #2  0x00000000004243a4 in terminate_due_to_signal (sig=sig@entry=8,
> backtrace_limit=backtrace_limit@entry=40) at emacs.c:470
> #3  0x00000000004248fc in handle_fatal_signal (sig=sig@entry=8) at sysdep.c:1800
> #4  0x000000000056f568 in deliver_thread_signal (sig=8,
> handler=0x4248f1 <handle_fatal_signal>) at sysdep.c:1792
> #5  0x000000000056f669 in deliver_fatal_thread_signal (sig=<optimized
> out>) at sysdep.c:1812
> #6  <signal handler called>
> #7  0x000000000069e35e in pixel_to_char_size
> (pixel_width=pixel_width@entry=482,
> pixel_height=pixel_height@entry=76,
> char_width=char_width@entry=0x7ffced20da38,
> char_height=char_height@entry=0x7ffced20da3c,
>     ew=<optimized out>) at widget.c:172

That code reads:

static void
pixel_to_char_size (EmacsFrame ew, Dimension pixel_width,
		    Dimension pixel_height, int *char_width, int *char_height)
{
  struct frame *f = ew->emacs_frame.frame;

  *char_width = FRAME_PIXEL_WIDTH_TO_TEXT_COLS (f, (int) pixel_width);
  *char_height = FRAME_PIXEL_HEIGHT_TO_TEXT_LINES (f, (int) pixel_height);
}

Which gets a frame pointer from a structure (ew) that MPS doesn't know
about; but frames can move, so that explains the bug, because MPS
doesn't know to update the pointer in the EmacsFrame structure.

Unfortunately, the structure is allocated by XtCreateWidget, which calls
malloc(), IIUC. So it's not immediately obvious (to me) how to fix it.
My best idea so far is to create an ambiguous root covering the frame
pointer and store that in the structure instead.

Pip