linux-kernel - Re: [PATCH] selftests/exec: Check if the syscall exists and bail if not

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Date:	Wed, 21 Jan 2015 10:22:04 +0000
From:	David Drysdale <drysdale@...gle.com>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Shuah Khan <shuahkh@....samsung.com>, davej@...emonkey.org.uk
Subject: Re: [PATCH] selftests/exec: Check if the syscall exists and bail if not

On Wed, Jan 21, 2015 at 7:41 AM, Michael Ellerman <mpe@...erman.id.au> wrote:
> On systems which don't implement sys_execveat(), this test produces a
> lot of output.
>
> Add a check at the beginning to see if the syscall is present, and if
> not just note one error and return.

Good point, thanks.

> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
> ---
>  tools/testing/selftests/exec/execveat.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/tools/testing/selftests/exec/execveat.c b/tools/testing/selftests/exec/execveat.c
> index e238c9559caf..b87e4a843bea 100644
> --- a/tools/testing/selftests/exec/execveat.c
> +++ b/tools/testing/selftests/exec/execveat.c
> @@ -234,6 +234,14 @@ static int run_tests(void)
>         int fd_cloexec = open_or_die("execveat", O_RDONLY|O_CLOEXEC);
>         int fd_script_cloexec = open_or_die("script", O_RDONLY|O_CLOEXEC);
>
> +       /* Check if we have execveat at all, and bail early if not */
> +       errno = 0;
> +       execveat_(-1, NULL, NULL, NULL, 0);
> +       if (errno == -ENOSYS) {

Could we change this to ENOSYS (no minus) and also change
the execveat_() function similarly, so that a binary built where
__NR_execveat is available but running where it isn't also exits
early?  (My bad for having the minus sign in execveat_() in the
first place -- fingers too used to kernel mode.)

Thanks!

> +               printf("[FAIL] ENOSYS calling execveat - no kernel support?\n");
> +               return 1;
> +       }
> +
>         /* Change file position to confirm it doesn't affect anything */
>         lseek(fd, 10, SEEK_SET);
>
> --
> 2.1.0
>
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