Re: [PATCH] linux-user: Remove unnecessary static assert involving __SIGRTMAX

[Philippe Mathieu-Daudé]

On 5/26/21 6:39 AM, Michael Forney wrote:
> Since "linux-user: fix use of SIGRTMIN" (6bc024e7), qemu removed
> use of __SIGRTMAX except for in this QEMU_BUILD_BUG_ON assert.
> Presumably, this check is to ensure that the loop in signal_table_init
> from SIGRTMIN to SIGRTMAX falls within the bounds of
> host_to_target_signal_table (_NSIG).
> 
> However, _NSIG is already defined to be the one larger than the
> largest signal supported by the system (as specified in the upcoming
> POSIX revision[0]), so the check is unnecessary.
> 
> musl libc does not define __SIGRTMAX, so removing this check fixes
> one of the last remaining errors when building qemu.
> 
> [0] https://www.austingroupbugs.net/view.php?id=741
> 
> Signed-off-by: Michael Forney <mforney@mforney.org>
> ---
> If you prefer, I can send an alternate patch to leave the
> QEMU_BUILD_BUG_ON, but guard it by #ifdef __SIGRTMAX.

This looks safer, personally I prefer, but let's see what the
maintainers prefer.

>  linux-user/signal.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/linux-user/signal.c b/linux-user/signal.c
> index 9016896dcd..6f62f2b528 100644
> --- a/linux-user/signal.c
> +++ b/linux-user/signal.c
> @@ -38,7 +38,6 @@ static void host_signal_handler(int host_signum, siginfo_t 
> *info,
>   * Signal number 0 is reserved for use as kill(pid, 0), to test whether
>   * a process exists without sending it a signal.
>   */
> -QEMU_BUILD_BUG_ON(__SIGRTMAX + 1 != _NSIG);
>  static uint8_t host_to_target_signal_table[_NSIG] = {
>      [SIGHUP] = TARGET_SIGHUP,
>      [SIGINT] = TARGET_SIGINT,
>