powerpc: Clear branch trap (MSR.BE) before delivering SIGTRAP
authorMatt Evans <matt@ozlabs.org>
Mon, 26 Mar 2018 16:55:21 +0000 (17:55 +0100)
committerMichael Ellerman <mpe@ellerman.id.au>
Sun, 1 Apr 2018 12:15:33 +0000 (22:15 +1000)
commit0e524e761fc2157f1037e0f5d616cd39e468d89c
treeeb7c275ed3c776f36de13f59fb65c2d4023f83af
parent4b7e5532d2113d002aa54bfe581f35b3f1f72306
powerpc: Clear branch trap (MSR.BE) before delivering SIGTRAP

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@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
arch/powerpc/kernel/traps.c