Re: [LTP] [PATCH] syscalls/waitid10: Fix on ARM, PPC and possibly others

[Richard Palethorpe <rpalethorpe@suse.de>]

Hello,

Cyril Hrubis <chrubis@suse.cz> writes:

> Hi!
>> While integer division by zero does trap on x86_64 and causes the SIGFPE
>> signal to be delivered it's not the case on all architecutes. At least
>> on ARM and PPC64LE division by zero simply returns undefined result
>> instead.

Nit picking: even with this patch we are still testing undefined
behaviour.

   There are six signals that can be delivered as a consequence of a
   hardware exception: SIGBUS, SIGEMT, SIGFPE, SIGILL, SIGSEGV, and
   SIGTRAP.  Which of these signals is delivered, for any given
   hard- ware exception, is not documented and does not always make
   sense.

If dividing by zero produces SIGEMT then it's still valid according to
the specification. FPE does stand for floating point exception, but we
are dividing integers.

>> 
>> This patch adds raise(SIGFPE) at the end of the child as a fallback to
>> make sure the process is killed with the right signal on all
>> architectures.
>> 
>> Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
>> ---
>>  testcases/kernel/syscalls/waitid/waitid10.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>> 
>> diff --git a/testcases/kernel/syscalls/waitid/waitid10.c b/testcases/kernel/syscalls/waitid/waitid10.c
>> index 869ef18bd..8c351d120 100644
>> --- a/testcases/kernel/syscalls/waitid/waitid10.c
>> +++ b/testcases/kernel/syscalls/waitid/waitid10.c
>> @@ -28,7 +28,10 @@ static void run(void)
>>  		volatile int a, zero = 0;
>>  
>>  		a = 1 / zero;
>> -		exit(a);
>> +
>> +		tst_res(TINFO, "Division by zero didn't trap, raising SIGFPE");
>
> This patch inroduces 'set but not used' warning for the a variable so
> maybe the message should look like:
>
> 		tst_res(TINFO, "1/0 = %i raising SIGFPE", a);
>
>> +		raise(SIGFPE);

I'm wondering if we should branch on the architecture. If it's x86[_64]
then we only do divide by zero as it's reasonable to think that if the
signal is not raised then this is a bug.

>>  	}
>>  
>>  	TST_EXP_PASS(waitid(P_ALL, 0, infop, WEXITED));
>> -- 
>> 2.34.1
>> 
>> 
>> -- 
>> Mailing list info: https://lists.linux.it/listinfo/ltp
>
> -- 
> Cyril Hrubis
> chrubis@suse.cz


-- 
Thank you,
Richard.

-- 
Mailing list info: https://lists.linux.it/listinfo/ltp