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Re: [Qemu-devel] [PATCH] syscall: fix special case of write(fd, NULL, 0)


From: Oliver Smith
Subject: Re: [Qemu-devel] [PATCH] syscall: fix special case of write(fd, NULL, 0)
Date: Wed, 14 Feb 2018 23:33:00 +0000

Hello there,

I'm a little late to the party. But what is necessary to get this
upstreamed, and how can I help?

PS: Sorry if I picked the wrong e-mail addresses, I wasn't subscribed to
the ML at that point and used the addresses I could find for the people
who answered to the original thread here:

https://lists.gnu.org/archive/html/qemu-devel/2017-09/msg08073.html

Thanks,
Oliver


From: Zhuowei Zhang <address@hidden>
> Linux returns success for the special case of calling write with a
> zero-length NULL buffer: compiling and running
>
> ```
>
> int main() {
>    ssize_t ret = write(STDOUT_FILENO, NULL, 0);
>    fprintf(stderr, "write returned %ld\n", ret);
>    return 0;
> }
> ```
> gives "write returned 0" when run directly, but "write returned -1" in
> QEMU.
>
> This commit checks for this situation and returns success if found.
>
> Signed-off-by: Zhuowei Zhang <address@hidden>
> ---
>  linux-user/syscall.c | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 9b6364a..ecadf49 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -7783,6 +7783,11 @@ abi_long do_syscall(void *cpu_env, int num,
abi_long
> arg1,
>          }
>          break;
>      case TARGET_NR_write:
> +        if (arg2 == 0 && arg3 == 0) {
> +            /* special case: write(fd, NULL, 0) returns success. */
> +            ret = 0;
> +            break;
> +        }
>          if (!(p = lock_user(VERIFY_READ, arg2, arg3, 1)))
>              goto efault;
>          if (fd_trans_target_to_host_data(arg1)) {
> --
> 1.9.1




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