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Date: Fri, 6 Aug 2010 14:44:56 +0200
From: Oleg Nesterov <oleg@redhat.com>
To: "Zhang, Wei-Jovi (NSN - CN/Hangzhou)" <wei-jovi.zhang@nsn.com>
Cc: akpm@linux-foundation.org, mingo@elte.hu, peterz@infradead.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH]exit.c: support larger exit code
Message-ID: <20100806124456.GA9107@redhat.com>
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On 08/06, Zhang, Wei-Jovi (NSN - CN/Hangzhou) wrote:
>
> Nowadays userspace application use systemcall exit/exit_group only
> support one byte exit code.
> In some cases this exit code range is too small for some "big
> application"(like telecom software, 255 is not enough).
>
> So we can give some "big application" a chance to get larger exit code
> from child process.
> For other application don't want use larger exit code, they can use
> marco WEXITSTATUS to get lower one byte exit code.
>
> #define WEXITSTATUS(status)   __WEXITSTATUS (__WAIT_INT (status))
> --- stdlib.h
> #define       __WEXITSTATUS(status)   (((status) & 0xff00) >> 8)
> --- usrbits/waitstatus.h
>
>
> diff --git a/kernel/exit.c b/kernel/exit.c
> index ceffc67..8b13676 100644
> --- a/kernel/exit.c
> +++ b/kernel/exit.c
> @@ -1045,7 +1045,7 @@ EXPORT_SYMBOL(complete_and_exit);
>
>  SYSCALL_DEFINE1(exit, int, error_code)
>  {
> -       do_exit((error_code&0xff)<<8);
> +       do_exit(error_code << 8);
>  }
>
>  /*
> @@ -1086,7 +1086,7 @@ do_group_exit(int exit_code)
>   */
>  SYSCALL_DEFINE1(exit_group, int, error_code)
>  {
> -       do_group_exit((error_code & 0xff) << 8);
> +       do_group_exit(error_code << 8);
>         /* NOTREACHED */
>         return 0;
>  }

Hmm. Looking at this patch, I am wondering what was the reason for the
current one-byte limitation.

I think the patch is fine. si_status, wo_stat are int too, so I do not
see any possibility for truncation before reporting to user-space.

Oleg.