Re: [hackers] [dwm][PATCH] do not call signal-unsafe function inside sighanlder

From: François-Xavier Carton <fx.carton91_AT_gmail.com>
Date: Tue, 19 Jul 2022 00:05:48 +0200

On Thu, Jul 14, 2022 at 07:26:40AM +0600, NRK wrote:
> die() calls vprintf, fputc and exit; none of these are
> async-signal-safe, see `man 7 signal-safety`.
> ---
> dwm.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/dwm.c b/dwm.c
> index 5646a5c..8358fb0 100644
> --- a/dwm.c
> +++ b/dwm.c
> _AT_@ -1541,6 +1541,8 @@ setup(void)
> Atom utf8string;
>
> /* clean up any zombies immediately */
> + if (signal(SIGCHLD, sigchld) == SIG_ERR)
> + die("can't install SIGCHLD handler:");
> sigchld(0);
>
> /* init screen */
> _AT_@ -1638,8 +1640,6 @@ showhide(Client *c)
> void
> sigchld(int unused)
> {
> - if (signal(SIGCHLD, sigchld) == SIG_ERR)
> - die("can't install SIGCHLD handler:");

Technically, no standard guarantees that the handler stays after being
called once. The implementation could reset it to the default action.
One may want to re-add a call to signal here, without error checking, to
ensure the handler remains in case SIGCHLD is raised multiple times.

> while (0 < waitpid(-1, NULL, WNOHANG));
> }
>
> --
> 2.35.1
>
>
Received on Tue Jul 19 2022 - 00:05:48 CEST