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[Bug tapsets/15219] New: syscall.exp failures on RHEL5, RHEL6, and rawhide


http://sourceware.org/bugzilla/show_bug.cgi?id=15219

             Bug #: 15219
           Summary: syscall.exp failures on RHEL5, RHEL6, and rawhide
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tapsets
        AssignedTo: systemtap@sourceware.org
        ReportedBy: dsmith@redhat.com
    Classification: Unclassified


While investigating bug #15211, I realized that we were seeing some common
failures in syscall.exp across kernel versions:

On RHEL5 (2.6.18-308.20.1.el5 x86_64) and RHEL6 (2.6.32-279.14.1.el6.x86_64), I
see the following failures:

====
FAIL: 32-bit clock syscall
FAIL: 32-bit rt_signal syscall
FAIL: 32-bit timer syscall
====

On rawhide (3.8.0-0.rc6.git1.1.fc19.x86_64), I see the following failures:

====
FAIL: 32-bit clock syscall
FAIL: 32-bit timer syscall
====

>From looking at systemtap.log, the failures all happen when the 32-bit compat
version of syscalls call the "real" syscall. The systemtap tapset has trouble
decoding the arguments.  For example:

timer: timer_settime (0, 1, UNKNOWN, 0xffff880014eeff30) = -22 (EINVAL)

That "UNKNOWN" value is coming from _struct_itimerspec_u(). Inside
_struct_itimerspec_u(), we return "UNKNOWN" when _stp_copy_from_user() fails.
In this case, _stp_copy_from_user() is failing because the memory it is reading
really isn't user memory. The 32-bit compat version of timer_settime() copies
the 'struct compat_itimerspec' pointer into a real 'struct itimerspec', then
calls the real sys_timer_settime().

We may need to loosen up _stp_copy_from_user().

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