Getting rid of alignment faults in userspace
dave.martin at linaro.org
Mon Jun 20 10:33:36 UTC 2011
On Fri, Jun 17, 2011 at 03:23:49PM -0700, Steve Langasek wrote:
> On Fri, Jun 17, 2011 at 01:10:11PM +0100, Dave Martin wrote:
> > For ARM, we can achieve the goal by augmenting the default kernel command-
> > line options: either
> > alignment=3
> > Fix up each alingment fault, but also log the faulting address
> > and name of the offending process to dmesg.
> > alignment=5
> > Pass each alignment fault to the user process as SIGBUS (fatal
> > by default) and log the faulting address and name of the
> > offending process to dmesg.
> > Fault statistics cat also be obtained at runtime by reading
> > /proc/cpu/alignment.
> > For other architectures, there may be other arch-specific ways of
> > achieving something similar.
> Other architectures use the 'prctl' tool, which uses the
> prctl(PR_SET_UNALIGN,...) kernel interface to control the unaligned trap
> behavior for the process. If this can be sanely togglable on ARM at
> runtime, it would be keen to use the same interface on this arch.
I guess that would be a new task for someone, if we consider it important
enough -- I'll raise it at today's linaro kernel working group meeting.
I don't know if that prctl call is wired up at all on arm kernels, but
it certainly won't work for v6/v7 at present. Enabling it looks fairly
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