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SubjectRe: [PATCH v5 10/10] LoongArch/ftrace: Fix unwind state when option func_stack_trace
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On 2022/10/28 上午10:56, Huacai Chen wrote:
> Hi, Qing,
>
> Can this patch be squashed to a previous one?
>
ok, I'll combine this patch with the previous patch.

Thanks
- Qing

> Huacai
>
> On Mon, Sep 19, 2022 at 11:19 AM Qing Zhang <zhangqing@loongson.cn> wrote:
>>
>> Ftrace plays like function head exception, prologue analysis will stop soon
>> because PC is at entry.
>>
>> 90000000004c5a54 <callee>:
>> 90000000004c5a54: 03400000 andi $zero, $zero, 0x0 ==>move t0, ra
>> 90000000004c5a58: 03400000 andi $zero, $zero, 0x0 ==>bl callsite
>> ==>90000000004c5a5c: 02fcc063 addi.d $sp, $sp, -208(0xf30)
>> ...
>>
>> When encountering ftrace_call, save trace function ra at PT_ERA, save
>> parent ra at PT_R1, At this time, pc is the position after the two nops
>> of callee. There is no conventional prologue operation between this
>> position and the function entry, so we need to reset the first flag to
>> make the caller continue to unwind.
>>
>> testing method:
>> echo path_openat > ./set_ftrace_filter
>> echo 1 > ./options/func_stack_trace
>> echo function > ./current_tracer
>>
>> Reported-by: Jeff Xie <xiehuan09@gmail.com>
>> Tested-by: Jinyang He <hejinyang@loongson.cn>
>> Tested-by: Jeff Xie <xiehuan09@gmail.com>
>> Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
>> ---
>> arch/loongarch/include/asm/unwind.h | 2 +-
>> arch/loongarch/kernel/unwind_prologue.c | 35 +++++++++++++++++++++----
>> 2 files changed, 31 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/loongarch/include/asm/unwind.h b/arch/loongarch/include/asm/unwind.h
>> index f66b07c3e6a1..f2b52b9ea93d 100644
>> --- a/arch/loongarch/include/asm/unwind.h
>> +++ b/arch/loongarch/include/asm/unwind.h
>> @@ -20,7 +20,7 @@ struct unwind_state {
>> char type; /* UNWINDER_XXX */
>> struct stack_info stack_info;
>> struct task_struct *task;
>> - bool first, error;
>> + bool first, error, is_ftrace;
>> int graph_idx;
>> unsigned long sp, pc, ra;
>> };
>> diff --git a/arch/loongarch/kernel/unwind_prologue.c b/arch/loongarch/kernel/unwind_prologue.c
>> index f77f3b6f3f06..4fb4923b68cc 100644
>> --- a/arch/loongarch/kernel/unwind_prologue.c
>> +++ b/arch/loongarch/kernel/unwind_prologue.c
>> @@ -14,9 +14,7 @@ unsigned long unwind_get_return_address(struct unwind_state *state)
>>
>> if (unwind_done(state))
>> return 0;
>> - else if (state->type)
>> - return state->pc;
>> - else if (state->first)
>> + else if (state->type || state->first)
>> return state->pc;
>>
>> return *(unsigned long *)(state->sp);
>> @@ -42,16 +40,41 @@ static bool unwind_by_guess(struct unwind_state *state)
>> return false;
>> }
>>
>> +static inline void unwind_state_fixup(struct unwind_state *state)
>> +{
>> +#ifdef CONFIG_FUNCTION_TRACER
>> + static unsigned long ftrace_case = (unsigned long)ftrace_call + 4;
>> +
>> + if (state->pc == ftrace_case)
>> + state->is_ftrace = true;
>> +#endif
>> +}
>> +
>> static bool unwind_by_prologue(struct unwind_state *state)
>> {
>> struct stack_info *info = &state->stack_info;
>> union loongarch_instruction *ip, *ip_end;
>> unsigned long frame_size = 0, frame_ra = -1;
>> unsigned long size, offset, pc = state->pc;
>> + struct pt_regs *regs;
>>
>> if (state->sp >= info->end || state->sp < info->begin)
>> return false;
>>
>> + if (state->is_ftrace) {
>> + /*
>> + * As we meet ftrace_regs_entry, reset first flag like first doing
>> + * tracing, Prologue analysis will stop soon because PC is at entry.
>> + */
>> + regs = (struct pt_regs *)state->sp;
>> + state->pc = regs->csr_era;
>> + state->ra = regs->regs[1];
>> + state->sp = regs->regs[3];
>> + state->first = true;
>> + state->is_ftrace = false;
>> + return true;
>> + }
>> +
>> if (!kallsyms_lookup_size_offset(pc, &size, &offset))
>> return false;
>>
>> @@ -97,7 +120,7 @@ static bool unwind_by_prologue(struct unwind_state *state)
>>
>> state->pc = *(unsigned long *)(state->sp + frame_ra);
>> state->sp = state->sp + frame_size;
>> - return !!__kernel_text_address(state->pc);
>> + goto out;
>>
>> first:
>> state->first = false;
>> @@ -106,7 +129,9 @@ static bool unwind_by_prologue(struct unwind_state *state)
>>
>> state->pc = state->ra;
>>
>> - return !!__kernel_text_address(state->ra);
>> +out:
>> + unwind_state_fixup(state);
>> + return !!__kernel_text_address(state->pc);
>> }
>>
>> void unwind_start(struct unwind_state *state, struct task_struct *task,
>> --
>> 2.36.1
>>

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