arm64: debug: avoid resetting stepping state machine when TIF_SINGLESTEP
authorWill Deacon <will.deacon@arm.com>
Fri, 26 Aug 2016 10:36:39 +0000 (11:36 +0100)
committerWill Deacon <will.deacon@arm.com>
Wed, 31 Aug 2016 16:49:19 +0000 (17:49 +0100)
commit3a402a709500c5a3faca2111668c33d96555e35a
tree97954886176d3534ea17350450d6c15548abaac8
parent675b0563d6b26aa97bb8fe5bbde0ab9dc358433b
arm64: debug: avoid resetting stepping state machine when TIF_SINGLESTEP

When TIF_SINGLESTEP is set for a task, the single-step state machine is
enabled and we must take care not to reset it to the active-not-pending
state if it is already in the active-pending state.

Unfortunately, that's exactly what user_enable_single_step does, by
unconditionally setting the SS bit in the SPSR for the current task.
This causes failures in the GDB testsuite, where GDB ends up missing
expected step traps if the instruction being stepped generates another
trap, e.g. PTRACE_EVENT_FORK from an SVC instruction.

This patch fixes the problem by preserving the current state of the
stepping state machine when TIF_SINGLESTEP is set on the current thread.

Cc: <stable@vger.kernel.org>
Reported-by: Yao Qi <yao.qi@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
arch/arm64/kernel/debug-monitors.c