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

[Brice Goglin <Brice.Goglin@inria.fr>]

Le 09/04/2020 à 17:27, Alex Bennée a écrit :
> Brice Goglin <Brice.Goglin@inria.fr> writes:
>
>> 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 <philmd@redhat.com>
>> Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
>>
>> 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, ") ");
> why not just use a format string:
>
>   snprintf(buf, sizeof(buf), "(%.125s) ", ts->bprm->argv[0]);
>

Go ahead and apply what you want (maybe 124 instead of 125 because of
the ending \0).

My commit message above explains how to test things very quickly.

I don't use qemu-user or Guix myself, and I can't spend time
debugging/testing this further.

Thank you

Brice