Re: linux-user: keep the name-ending parenthesis in /proc/self/stat

[Laurent Vivier]

Le 08/04/2020 à 10:24, Brice Goglin a écrit :
> When the program name is very long, qemu-user may truncate it in
> /proc/self/stat. However the truncation must keep the ending ") "
> to conform to the proc manpage which says:
>     (2) comm  %s
>            The  filename of the executable, in parentheses.  This
>            is visible whether or not the  executable  is  swapped
>            out.
> 
> To reproduce:
> $ ln -s /bin/cat <filenamewithmorethan128chars>
> $ qemu-x86_64 ./<filenamewithmorethan128chars> /proc/self/stat
> 
> Before the patch, you get:
> 1134631 (<filenametruncated>0 0 0 0 0 0 0 0 ...
> After the patch:
> 1134631 (<filenametruncat>) 0 0 0 0 0 0 0 0 ...
> 
> This fixes an issue with hwloc failing to parse /proc/self/stat
> when Ludovic Courtes was testing it in Guix over qemu-aarch64.
> 
> Signed-off-by: Philippe_Mathieu-Daudé <address@hidden>

You can't add "Signed-off-by" of someone else, in this case you could
add "Suggested-by:".

The subject of your patch should include "[PATCH]" (and the version of
the patch, "[PATCH v2]").

https://wiki.qemu.org/Contribute/SubmitAPatch

> Signed-off-by: Brice Goglin <address@hidden>
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -7305,7 +7305,11 @@ static int open_self_stat(void *cpu_env, int fd)
>          snprintf(buf, sizeof(buf), "%"PRId64 " ", val);
>        } else if (i == 1) {
>          /* app name */
> -        snprintf(buf, sizeof(buf), "(%s) ", ts->bprm->argv[0]);
> +        char *ptr = buf;
> +
> +        *ptr++ = '(';
> +        ptr = stpncpy(ptr, ts->bprm->argv[0], sizeof(buf) - 3);

To have space for the NUL character I think it should be "sizeof(buf) - 4".

> +        strcpy(ptr, ") ");
>        } else if (i == 27) {
>          /* stack bottom */
>          val = start_stack;
> 

Thanks,
Laurent