Subject: bug#58960: 29.0.50; Assert fails when browsing an URL, bug#58960: 29.0.50; Assert fails when browsing an URL

From: Robert Pluim <[email-masked]>
Date: Wed, 02 Nov 2022 14:58:23 +0100

>>>>> On Wed, 02 Nov 2022 15:10:07 +0200, Eli Zaretskii <[email-masked]> said:

    >> Cc: Gerd Möllmann <[email-masked]>,
    >> [email-masked]
    >> From: Robert Pluim <[email-masked]>
    >> Date: Wed, 02 Nov 2022 11:20:31 +0100
    >> 
    >> Looks like `call-process' needs to ensure the child signal fdʼs are
    >> set up before calling `emacs_spawn'.

    Eli> Why do we need this?  IOW, do you understand how did SIGCHLD cause
    Eli> this?

`browse-url' does `call-process' for `xdg-open' by default. `xdg-open'
exits almost immediately, we get SIGCHLD:

(gdb) bt
#0  terminate_due_to_signal (sig=6, backtrace_limit=2147483647) at emacs.c:421
#1  0x00005555555b489e in die
    (msg=msg@entry=0x5555558d938f "0 <= fd", file=file@entry=0x5555558d9354 "process.c", line=line@entry=7386) at alloc.c:7692
#2  0x00005555555bfec9 in child_signal_notify () at process.c:7386
#3  handle_child_signal (sig=<optimized out>) at process.c:7493
#4  0x000055555574e992 in deliver_process_signal
    (sig=17, handler=0x555555831b40 <handle_child_signal>) at sysdep.c:1741
#5  0x00007ffff5752140 in <signal handler called> ()

`child_signal_notify' does this:

  int fd = child_signal_write_fd;
  eassert (0 <= fd);

and if `child_signal_init' hasnʼt been called, then this is still
true:

/* The write end thereof.  The SIGCHLD handler writes to this file
   descriptor to notify `wait_reading_process_output' of process
   status changes.  */
static int child_signal_write_fd = -1;

so the assert fails.

Why canʼt we just call `child_signal_init' from `init_process_emacs'
instead of `create_process'?

Robert
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