Re: Duplicate events for 32-bit compatible syscall probes

[David Smith <dsmith at redhat dot com>]

On 04/25/2013 08:12 AM, David Smith wrote:
> On 04/24/2013 04:47 AM, Aryeh Weinreb wrote:
>> Hi,
>>
>> While using some syscall.mq_* probes on 32bit on x86_64 I am getting
>> duplicate events.
>>
>> Looking into ipc/compat_mq.c it seems that the compat_sys_mq calls are
>> just wrappers for the sys_mq ones.
>> Although, sometimes the compat calls can return EFAULT without calling
>> the non-compat versions.
>>
>> It would be nice to only get one event for each system call without
>> missing any calls.
>>
>> I am using an RHEL 6 build of systemtap version 1.8.
> 
> If you just want to trace the "real" 64-bit syscalls, I'd do something
> like the following to reject the 32-bit-on-64-bit syscalls. Note that
> this is untested, but should work.
> 
> =====
> function is_compat_task:long () %{
>     STAP_RETVALUE = _stp_is_compat_task();
> %}
> 
> probe syscall.mq_getsetattr
> {
> 	if { is_compat_task() } next;
> 	# ... your real code here
> }
> =====
> 

And of course as soon as I send this I realize it won't work. That will
most likely reject all 32-on-64 processes.

I'll keep thinking here.

-- 
David Smith
dsmith@redhat.com
Red Hat
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