@@ -104,6 +104,7 @@ void user_regs_reset_single_step(struct user_pt_regs *regs,
void kernel_enable_single_step(struct pt_regs *regs);
void kernel_disable_single_step(void);
int kernel_active_single_step(void);
+void kernel_rewind_single_step(struct pt_regs *regs);
#ifdef CONFIG_HAVE_HW_BREAKPOINT
int reinstall_suspended_bps(struct pt_regs *regs);
@@ -438,6 +438,11 @@ int kernel_active_single_step(void)
}
NOKPROBE_SYMBOL(kernel_active_single_step);
+void kernel_rewind_single_step(struct pt_regs *regs)
+{
+ set_regs_spsr_ss(regs);
+}
+
/* ptrace API */
void user_enable_single_step(struct task_struct *task)
{
@@ -224,6 +224,8 @@ int kgdb_arch_handle_exception(int exception_vector, int signo,
*/
if (!kernel_active_single_step())
kernel_enable_single_step(linux_regs);
+ else
+ kernel_rewind_single_step(linux_regs);
err = 0;
break;
default:
Currently only the first attempt to single-step has any effect. After that all further stepping remains "stuck" at the same program counter value. Refer to the ARM Architecture Reference Manual (ARM DDI 0487E.a) D2.12, PSTATE.SS=1 should be set at each step before transferring the PE to the 'Active-not-pending' state. The problem here is PSTATE.SS=1 is not set since the second single-step. After the first single-step, the PE transferes to the 'Inactive' state, with PSTATE.SS=0 and MDSCR.SS=1, thus PSTATE.SS won't be set to 1 due to kernel_active_single_step()=true. Then the PE transferes to the 'Active-pending' state when ERET and returns to the debugger by step exception. Before this patch: ================== Entering kdb (current=0xffff3376039f0000, pid 1) on processor 0 due to Keyboard Entry [0]kdb> [0]kdb> [0]kdb> bp write_sysrq_trigger Instruction(i) BP #0 at 0xffffa45c13d09290 (write_sysrq_trigger) is enabled addr at ffffa45c13d09290, hardtype=0 installed=0 [0]kdb> go $ echo h > /proc/sysrq-trigger Entering kdb (current=0xffff4f7e453f8000, pid 175) on processor 1 due to Breakpoint @ 0xffffad651a309290 [1]kdb> ss Entering kdb (current=0xffff4f7e453f8000, pid 175) on processor 1 due to SS trap @ 0xffffad651a309294 [1]kdb> ss Entering kdb (current=0xffff4f7e453f8000, pid 175) on processor 1 due to SS trap @ 0xffffad651a309294 [1]kdb> After this patch: ================= Entering kdb (current=0xffff6851c39f0000, pid 1) on processor 0 due to Keyboard Entry [0]kdb> bp write_sysrq_trigger Instruction(i) BP #0 at 0xffffc02d2dd09290 (write_sysrq_trigger) is enabled addr at ffffc02d2dd09290, hardtype=0 installed=0 [0]kdb> go $ echo h > /proc/sysrq-trigger Entering kdb (current=0xffff6851c53c1840, pid 174) on processor 1 due to Breakpoint @ 0xffffc02d2dd09290 [1]kdb> ss Entering kdb (current=0xffff6851c53c1840, pid 174) on processor 1 due to SS trap @ 0xffffc02d2dd09294 [1]kdb> ss Entering kdb (current=0xffff6851c53c1840, pid 174) on processor 1 due to SS trap @ 0xffffc02d2dd09298 [1]kdb> ss Entering kdb (current=0xffff6851c53c1840, pid 174) on processor 1 due to SS trap @ 0xffffc02d2dd0929c [1]kdb> Fixes: 44679a4f142b ("arm64: KGDB: Add step debugging support") Co-developed-by: Wei Li <liwei391@huawei.com> Signed-off-by: Wei Li <liwei391@huawei.com> Signed-off-by: Sumit Garg <sumit.garg@linaro.org> Tested-by: Douglas Anderson <dianders@chromium.org> Acked-by: Daniel Thompson <daniel.thompson@linaro.org> Tested-by: Daniel Thompson <daniel.thompson@linaro.org> --- arch/arm64/include/asm/debug-monitors.h | 1 + arch/arm64/kernel/debug-monitors.c | 5 +++++ arch/arm64/kernel/kgdb.c | 2 ++ 3 files changed, 8 insertions(+)