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Re: utrace syscall arguments


Roland McGrath wrote:
>> [2] This might just be an system call that needs some extra processing
>> or a kernel problem.  RHBZ 495935 filed against this problem
>> (<https://bugzilla.redhat.com/show_bug.cgi?id=495935>)
> 
> That just looks like an strace bug for s390x biarch.
> I'm a little confused as to how your stap test suite cares what strace thinks.

The stap test doesn't really care what strace thinks.  But, when I get
odd results I always check them against what strace sees.  If strace and
stap see the same thing, it might be a kernel bug.  If only stap sees a
problem, I check further with strace.

For instance, on s390x, strace could decode the mmap call correctly for
64-bit executables but stap couldn't.  After running strace on strace, I
saw that strace did additional memory reads for mmap which the test now
does.

RHBZ 495935 shows that strace (and also stap, but I didn't mention that
in the bug) can't decode mmap calls correctly for 32-bit executables.

>> [3] This appears to be an ia64 specific systemtap problem that someone
>> with actual ia64 knowledge will need to look at.  For system calls that
>> fail, all arguments come back as zeros.
> 
> I'm confused.  You can only get the syscall arguments at entry time, before
> it is decided whether it succeeds or fails.  Or do you mean using a bogus
> system call number?

Actually, I meant both.  If the syscall fails or if I use a bogus
syscall number, the args all came back as 0.  Unfortunately, I can't
quite remember what strace did here.  I think it saw the arguments
correctly (but I'm not 100% sure).

-- 
David Smith
dsmith@redhat.com
Red Hat
http://www.redhat.com
256.217.0141 (direct)
256.837.0057 (fax)


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