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>
diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 2c1a1d2..a2ef0c0 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -471,7 +471,7 @@ static inline int check_io_access(struct pt_regs *regs)
/* single-step stuff */
#define single_stepping(regs) (current->thread.debug.dbcr0 & DBCR0_IC)
#define clear_single_step(regs) (current->thread.debug.dbcr0 &= ~DBCR0_IC)
-
+#define clear_br_trace(regs) do {} while(0)
#else
/* On non-4xx, the reason for the machine check or program
exception is in the MSR. */
@@ -484,6 +484,7 @@ static inline int check_io_access(struct pt_regs *regs)
#define single_stepping(regs) ((regs)->msr & MSR_SE)
#define clear_single_step(regs) ((regs)->msr &= ~MSR_SE)
+#define clear_br_trace(regs) ((regs)->msr &= ~MSR_BE)
#endif
#if defined(CONFIG_E500)
@@ -999,6 +1000,7 @@ void single_step_exception(struct pt_regs *regs)
enum ctx_state prev_state = exception_enter();
clear_single_step(regs);
+ clear_br_trace(regs);
if (kprobe_post_handler(regs))
return;