powerpc: Clear branch trap (MSR.BE) before delivering SIGTRAP

Wed Apr 4 02:03:42 AEST 2018

On Mon, 2018-03-26 at 16:55:21 UTC, Matt Evans wrote:
> When using SIG_DBG_BRANCH_TRACING, MSR.BE is left enabled in the
> user context when single_step_exception() prepares the SIGTRAP
> delivery.  The resulting branch-trap-within-the-SIGTRAP-handler
> isn't healthy.
> 
> Commit 2538c2d08f46141550a1e68819efa8fe31c6e3dc broke this, by
> replacing an MSR mask operation of ~(MSR_SE | MSR_BE) with a call
> to clear_single_step() which only clears MSR_SE.
> 
> This patch adds a new helper, clear_br_trace(), which clears the
> debug trap before invoking the signal handler.  This helper is a
> NOP for BookE as SIG_DBG_BRANCH_TRACING isn't supported on BookE.
> 
> Signed-off-by: Matt Evans <matt at ozlabs.org>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/0e524e761fc2157f1037e0f5d616cd

cheers