| Message ID | 20170523043058.5463-2-takahiro.akashi@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, May 23, 2017 at 01:30:55PM +0900, AKASHI Takahiro wrote: > After entering kgdb mode, the first 'stepi' can succeed, but the following > 'stepi' never executes the next instruction. > > This is because a software step cannot get enabled as the software step > bit(SS) in SPSR, which is cleared by the first single stepping, will not > be set again for the following 's' commands. For userspace, we have user_rewind_single_step to re-arm the state machine on an unhandled step exception. It sounds like we need the kernel version of that? > Please note that this bit, as well as the software step control bit(SS) > in MDSCR, must be set before resuming the execution. > kernel_active_single_step() called by kgdb_arch_handle_exception() checks > only for the bit in MDSCR, and so kgdb_enable_single_step() will never be > called. MDSCR.SS shouldn't get cleared by the hardware, so I don't understand your point here. Will
diff --git a/arch/arm64/kernel/kgdb.c b/arch/arm64/kernel/kgdb.c index 2122cd187f19..b9176b324e5a 100644 --- a/arch/arm64/kernel/kgdb.c +++ b/arch/arm64/kernel/kgdb.c @@ -197,12 +197,6 @@ int kgdb_arch_handle_exception(int exception_vector, int signo, atomic_set(&kgdb_cpu_doing_single_step, -1); kgdb_single_step = 0; - /* - * Received continue command, disable single step - */ - if (kernel_active_single_step()) - kernel_disable_single_step(); - err = 0; break; case 's': @@ -217,7 +211,6 @@ int kgdb_arch_handle_exception(int exception_vector, int signo, kgdb_arch_update_addr(linux_regs, remcom_in_buffer); atomic_set(&kgdb_cpu_doing_single_step, raw_smp_processor_id()); kgdb_single_step = 1; - /* * Enable single step handling */ @@ -252,6 +245,8 @@ static int kgdb_step_brk_fn(struct pt_regs *regs, unsigned int esr) if (!kgdb_single_step) return DBG_HOOK_ERROR; + kernel_disable_single_step(); + kgdb_handle_exception(1, SIGTRAP, 0, regs); return 0; }
After entering kgdb mode, the first 'stepi' can succeed, but the following 'stepi' never executes the next instruction. This is because a software step cannot get enabled as the software step bit(SS) in SPSR, which is cleared by the first single stepping, will not be set again for the following 's' commands. Please note that this bit, as well as the software step control bit(SS) in MDSCR, must be set before resuming the execution. kernel_active_single_step() called by kgdb_arch_handle_exception() checks only for the bit in MDSCR, and so kgdb_enable_single_step() will never be called. This patch removes kgdb_disable_single_step() from 'c' command handling and enables/disables a single step explicitly at every entry and exit of 's' command handling. Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Jason Wessel <jason.wessel@windriver.com> --- arch/arm64/kernel/kgdb.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-)