Re: Getting rid of alignment faults in userspace

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[1] 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.

HTH,