Red Hat Bugzilla – Bug 211652
crash generates floating point assist faults on ia64
Last modified: 2010-10-22 02:35:19 EDT
The gdb module in crash attempts to manipulate floating point values via ldexp
when printing backtraces. If the values in the fp registers contain
denormals/NANs, the kernel logs a floating point software assist fault.
The messages are low in volume and the concern is primarily cosmetic.
Steps to reproduce:
# rpm -ivh kernel-2.6.9-42.EL.ia64.rpm
# crash /usr/lib/debug/lib/modules/2.6.9-42.EL/vmlinux
crash> foreach bt
# dmesg|grep "assist fault"
kernel: crash(12028): floating-point assist fault at ip 20000000000d4382, isr
The ip is always inside ldexp, being called from the gdb value_print function
(see attached backtrace)
Created attachment 139001 [details]
backtrace from the location triggering the fp assist fault
Interesting, although I can't reproduce it, at least with 2.4.21-47.EL.
It looks like the messages can be turned off on a per-task basis
with a prctl PR_SET_FPEMU in order to set the IA64_THREAD_FPEMU_NOPRINT
bit in its current->thread.flags.
Created attachment 139012 [details]
prctl(PR_SET_FPEMU, 1, 0, 0, 0);
If you get the chance, can you apply this patch to the ia64.c file
in the crash utility sources, rebuild, and see if it clears up the
The patch is against the 4.0-3.7 version of crash, but will probably
apply to whatever you're using. But the easiest thing to do would
be to go to http://people.redhat.com/anderson and download the
crash-4.0-3.7.tar.gz file. Then:
# tar xzf crash-4.0-3.7.tar.gz
# cd crash-4.0-3.7
# patch -p0 < ia64_prctl.patch
and test it out.
Or, alternatively, this should accomplish the same thing with
the crash utility unmodified:
# prctl --fpemu=silent crash
Have tested both the prctl workaround and the patch (applied to the U4 crash
sources - went in fine with a bit of offset) - both worked like a charm, thanks!
This should go into the RHEL4-5 crash utility errata.
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux maintenance release. Product Management has requested
further review of this request by Red Hat Engineering, for potential
inclusion in a Red Hat Enterprise Linux Update release for currently deployed
products. This request is not yet committed for inclusion in an Update
I am currently filing the RHEL4-U5 crash utility errata, and
for inclusion this Bugzilla needs:
crash version 4.0-3.9 checked into RHEL4 CVS.
(still requires devel_ack+, qa_ack+ and rhel-4.5+)
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.