linux-kernel - Re: [PATCH v2] selftests/exec: Check if the syscall exists and bail if not

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Date:	Tue, 3 Feb 2015 07:58:59 +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 v2] selftests/exec: Check if the syscall exists and bail
 if not

On Tue, Feb 3, 2015 at 3:53 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.
>
> When we run on a system that doesn't implement the syscall we will get
> ENOSYS back from the kernel, so change the logic that handles
> __NR_execveat not being defined to also use ENOSYS rather than -ENOSYS.
>
> Signed-off-by: Michael Ellerman <mpe@...erman.id.au>

Acked-by: David Drysdale <drysdale@...gle.com>

> ---
>
> v2: Switch to positive ENOSYS. Confirmed this works as expected in the
> case where the syscall is defined, but then is not present at runtime.

Thanks!

>
>  tools/testing/selftests/exec/execveat.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/exec/execveat.c b/tools/testing/selftests/exec/execveat.c
> index e238c9559caf..8d5d1d2ee7c1 100644
> --- a/tools/testing/selftests/exec/execveat.c
> +++ b/tools/testing/selftests/exec/execveat.c
> @@ -30,7 +30,7 @@ static int execveat_(int fd, const char *path, char **argv, char **envp,
>  #ifdef __NR_execveat
>         return syscall(__NR_execveat, fd, path, argv, envp, flags);
>  #else
> -       errno = -ENOSYS;
> +       errno = ENOSYS;
>         return -1;
>  #endif
>  }
> @@ -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) {
> +               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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