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SubjectRe: [PATCH 1/6] LoongArch: Get frame info in unwind_start when regs is not supported
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Hi, Jinyang

On 2022/12/15 下午12:01, Jinyang He wrote:
> At unwind_start, it is better to try to get its frame info even we not
> support regs rather than get them outside. So that we can simply use
> unwind_{start, next_frame, done} outside.
>
> Signed-off-by: Jinyang He <hejinyang@loongson.cn>
> ---
> arch/loongarch/kernel/process.c | 12 +++---------
> arch/loongarch/kernel/unwind_guess.c | 6 ++++++
> arch/loongarch/kernel/unwind_prologue.c | 16 +++++++++++++---
> 3 files changed, 22 insertions(+), 12 deletions(-)
>
> diff --git a/arch/loongarch/kernel/process.c b/arch/loongarch/kernel/process.c
> index 502b8b950057..6ef45174ad35 100644
> --- a/arch/loongarch/kernel/process.c
> +++ b/arch/loongarch/kernel/process.c
> @@ -197,20 +197,14 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
>
> unsigned long __get_wchan(struct task_struct *task)
> {
> - unsigned long pc;
> + unsigned long pc = 0;
> struct unwind_state state;
>
> if (!try_get_task_stack(task))
> return 0;
>
> - unwind_start(&state, task, NULL);
> - state.sp = thread_saved_fp(task);
> - get_stack_info(state.sp, state.task, &state.stack_info);
> - state.pc = thread_saved_ra(task);
> -#ifdef CONFIG_UNWINDER_PROLOGUE
> - state.type = UNWINDER_PROLOGUE;
> -#endif
> - for (; !unwind_done(&state); unwind_next_frame(&state)) {
> + for (unwind_start(&state, task, NULL); !unwind_done(&state);
> + unwind_next_frame(&state)) {
> pc = unwind_get_return_address(&state);
> if (!pc)
> break;
> diff --git a/arch/loongarch/kernel/unwind_guess.c b/arch/loongarch/kernel/unwind_guess.c
> index e2d2e4f3001f..e03864511582 100644
> --- a/arch/loongarch/kernel/unwind_guess.c
> +++ b/arch/loongarch/kernel/unwind_guess.c
> @@ -26,6 +26,12 @@ void unwind_start(struct unwind_state *state, struct task_struct *task,
> if (regs) {
> state->sp = regs->regs[3];
> state->pc = regs->csr_era;
> + } else if (task == current) {
> + state->sp = (unsigned long)__builtin_frame_address(0);
> + state->pc = (unsigned long)__builtin_return_address(0);
> + } else {
> + state->sp = thread_saved_fp(task);
> + state->pc = thread_saved_ra(task);
>
The case for tasks is already handled in stacktrace.c, which is reusable
code:
void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
struct task_struct *task, struct pt_regs *regs)
{
...

if (task == current) {
regs->regs[3] = (unsigned long)__builtin_frame_address(0);
regs->csr_era = (unsigned long)__builtin_return_address(0);
} else {
regs->regs[3] = thread_saved_fp(task);
regs->csr_era = thread_saved_ra(task);
}
...
for (unwind_start(&state, task, regs);
!unwind_done(&state); unwind_next_frame(&state)) {
addr = unwind_get_return_address(&state);
...
}

>
> state->task = task;
> diff --git a/arch/loongarch/kernel/unwind_prologue.c b/arch/loongarch/kernel/unwind_prologue.c
> index 0f8d1451ebb8..9d51ea37782e 100644
> --- a/arch/loongarch/kernel/unwind_prologue.c
> +++ b/arch/loongarch/kernel/unwind_prologue.c
> @@ -141,12 +141,22 @@ void unwind_start(struct unwind_state *state, struct task_struct *task,
> struct pt_regs *regs)
> {
> memset(state, 0, sizeof(*state));
> + state->type = UNWINDER_PROLOGUE;
>
> - if (regs && __kernel_text_address(regs->csr_era)) {
> - state->pc = regs->csr_era;
> + if (regs) {
> state->sp = regs->regs[3];
> + state->pc = regs->csr_era;
> state->ra = regs->regs[1];
> - state->type = UNWINDER_PROLOGUE;
> + if (!__kernel_text_address(state->pc))
> + state->type = UNWINDER_GUESS;
> + } else if (task == current) {
> + state->sp = (unsigned long)__builtin_frame_address(0);
> + state->pc = (unsigned long)__builtin_return_address(0);
> + state->ra = 0;
> + } else {
> + state->sp = thread_saved_fp(task);
> + state->pc = thread_saved_ra(task);
> + state->ra = 0;
> }
>
also...
> state->task = task;
>
Thanks,
-Qing

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