Problems with the POSIX clocks and timers tests from HRT

[George Anzinger]

In running the tests in the HRT support package I found several cases where 
glibc code generated segment faults.  As the tests were written, mainly, to 
verify the kernel part of the POSIX clocks and timers, it may be that some of 
these problems are not important.  Here is what the tests found:

Clock_nanosleep() attempts to verify that the time being passed is normalized. 
The segv happens when a bad pointer is passed (the tests pass 0 and 1 and 
possibly others).

timer_delete() when given a bad pointer causes a segv.  This is caused by the 
glibc code assuming that the timer_id is a pointer.  (I wonder about this as it 
is passed to user code and he can do most anything.  A fair amount of work went 
into the kernel code to prevent bad timer ids from causing problems.  This also 
affects other things... see timer_get_overrun() below.

Clock_settime() is also trying to verify that the time is normalized and seg 
faults on a bad pointer.

timer_get_overrun() fails when passed a timer id from the sig_info block.  This 
seems to me like a real problem.  If a user writes a signal handler for timers 
and wants to know which of several timers he is working with he should be able 
to use the sig_info block timer_id to get this information.  glibc, however, 
prevents this by changing the timer_id into a pointer to a local bit of memory 
which contains the real timer_id.

In the case of clock_nanosleep() and clock_settime() I think the best thing to 
do is to just pass the stuff to the kernel and let it deal with it.

For timer_delete() and the timer indirection being done I need to guess.  I 
suspect that timer IDs are indirected to allow the "create thread on expire" 
option to work.  If this is the only reason, wouldn't it work just as well to 
set the timer up with a local (to glibc) signal handler.  Only such timers would 
need the extra memory.  I suppose I am missing something here.

For interested folks a version of the HRT tests that uses glibc (but only if 
CLOCK_MONOTONIC is defined) is in the HRT sourceforge cvs at

http://cvs.sourceforge.net/viewcvs.py/high-res-timers/HRT/

The patch is common_hrt_tests.patch.  (I just uploaded this and it takes a while 
for sourceforge to put it on the viewable system, so be patient if you don't see 
it.)  This is a kernel patch which ONLY adds directories to the kernel tree 
under Documentation/high-res-timers.  The make file in the tests dir should make 
all the tests.  The script do_test runs those I consider an acceptance test 
which brought the above problems to light.  The tests detect the absence of the 
high res clocks and do not attempt to test them.

Comments?
-- 
George Anzinger   george@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/