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

[Laurent Vivier <laurent@vivier.eu>]

Le 08/04/2020 à 08:40, Brice Goglin a écrit :
> Le 31/03/2020 à 00:29, Brice Goglin a écrit :
>> Le 31/03/2020 à 00:05, Philippe Mathieu-Daudé a écrit :
>>> On 3/30/20 9:07 PM, Brice Goglin wrote:
>>>> 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: Brice Goglin<Brice.Goglin@inria.fr>
>>>>
>>>> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
>>>> index 5af55fca78..a1126dcf5b 100644
>>>> --- a/linux-user/syscall.c
>>>> +++ b/linux-user/syscall.c
>>>> @@ -7305,7 +7305,10 @@ 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]);
>>>> +        len = snprintf(buf, sizeof(buf), "(%s) ", ts->bprm->argv[0]);
>>>> +        if (len >= sizeof(buf))
>>>> +          /* bring back the ending ") " that was truncated */
>>>> +          strcpy(buf+sizeof(buf)-3, ") ");
>>> Maybe we can avoid the sprintf() call:
>>>
>>> -- >8 --
>>> 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);
>>> +        strcpy(ptr, ") ");
>>>        } else if (i == 27) {
>>>          /* stack bottom */
>>>          val = start_stack;
>>>
>> This works too.
> 
> 
> Hello
> 
> Is anybody going to fix this anyhow for the next release?

Hi,

we are expecting you fix the patch according to Philippe's comment and
re-send it or explain why you don't want.

Thanks,
Laurent