From 43d95069729e96ca0cd1266ada99bd319c22d9a7 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Fri, 26 Aug 2016 11:36:39 +0100 Subject: [PATCH] arm64: debug: avoid resetting stepping state machine when TIF_SINGLESTEP commit 3a402a709500c5a3faca2111668c33d96555e35a upstream. 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. Reported-by: Yao Qi Signed-off-by: Will Deacon Signed-off-by: Ben Hutchings --- arch/arm64/kernel/debug-monitors.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c index a2db6f219bbe8..108dbbed5322b 100644 --- a/arch/arm64/kernel/debug-monitors.c +++ b/arch/arm64/kernel/debug-monitors.c @@ -427,8 +427,10 @@ int kernel_active_single_step(void) /* ptrace API */ void user_enable_single_step(struct task_struct *task) { - set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP); - set_regs_spsr_ss(task_pt_regs(task)); + struct thread_info *ti = task_thread_info(task); + + if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP)) + set_regs_spsr_ss(task_pt_regs(task)); } void user_disable_single_step(struct task_struct *task) -- 2.47.3