Commit 3ce70b2e authored Dec 01, 2010 by Will Deacon

ARM: hw_breakpoint: disallow per-cpu breakpoints without overflow handler

Single-stepping a breakpoint requires us to disable it temporarily so that
we don't get stuck in a recursive debug trap. With per-cpu breakpoints this
presents a problem where an interrupt can be taken before the single-step has
completed and a new task is eventually scheduled. This new task will not
hit the breakpoint because it will have been disabled during the previous
handling code.

This patch disallows per-cpu breakpoints on ARM when an overflow handler
is not present. A similar effect can be created by placing breakpoints on
a shell and then running applications there.

Signed-off-by: Will Deacon <will.deacon@arm.com>

parent 9ebb3cbc

arch/arm/kernel/hw_breakpoint.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -622,10 +622,12 @@ int arch_validate_hwbkpt_settings(struct perf_event *bp)
		* Currently we rely on an overflow handler to take
		* care of single-stepping the breakpoint when it fires.
		* In the case of userspace breakpoints on a core with V7 debug,
		* we can use the mismatch feature as a poor-man's hardware single-step.
		* we can use the mismatch feature as a poor-man's hardware
		* single-step, but this only works for per-task breakpoints.
		*/
		if (WARN_ONCE(!bp->overflow_handler &&
		(arch_check_bp_in_kernelspace(bp) \|\| !core_has_mismatch_brps()),
		(arch_check_bp_in_kernelspace(bp) \|\| !core_has_mismatch_brps()
		\|\| !bp->hw.bp_target),
		"overflow handler required but none found")) {
		ret = -EINVAL;
		}