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>
* 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;
}