Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 0e524e76 authored by Matt Evans's avatar Matt Evans Committed by Michael Ellerman
Browse files

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 2538c2d0 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: default avatarMatt Evans <matt@ozlabs.org>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 4b7e5532

arch/powerpc/kernel/traps.c

+3 −1
Original line number Diff line number Diff line
@@ -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;