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Subject: Re: [PATCH 4/6] LoongArch: Strip guess_unwinder out from
 prologue_unwinder
To:     Qing Zhang <zhangqing@loongson.cn>,
        Huacai Chen <chenhuacai@kernel.org>,
        WANG Xuerui <kernel@xen0n.name>
Cc:     loongarch@lists.linux.dev, linux-kernel@vger.kernel.org,
        Steven Rostedt <rostedt@goodmis.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>
References: <20221215040141.18610-1-hejinyang@loongson.cn>
 <20221215040141.18610-5-hejinyang@loongson.cn>
 <36c3560a-0a2d-4c3f-ecb6-0e7e71746917@loongson.cn>
 <be643b7c-611e-c87b-c030-5fa51220d78c@loongson.cn>
 <6fdb3dc9-2b34-ce53-1ff8-6b23c1eaaa82@loongson.cn>
From:   Jinyang He <hejinyang@loongson.cn>
Message-ID: <b1d090e3-1d68-3508-9108-5d697fa84ddd@loongson.cn>
Date:   Sat, 17 Dec 2022 09:47:45 +0800
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On 2022-12-16 10:14, Qing Zhang wrote:

> Hi, Jinyang
>
> On 2022/12/16 上午9:40, Jinyang He wrote:
>> On 2022-12-15 17:15, Qing Zhang wrote:
>>
>>> Hi, Jinyang
>>>
>>> On 2022/12/15 下午12:01, Jinyang He wrote:
>>>> The prolugue unwinder rely on symbol info. When PC is not in kernel
>>>> text address, it cannot find relative symbol info and it will be 
>>>> broken.
>>>> The guess unwinder will be used in this case. And the guess unwinder
>>>> codes in prolugue unwinder is redundant. Strip it out and set the
>>>> unwinder info in unwind_state.
>>>>
>>>> Signed-off-by: Jinyang He <hejinyang@loongson.cn>
>>>> ---
>>>>   arch/loongarch/include/asm/unwind.h     |  22 ++++
>>>>   arch/loongarch/kernel/Makefile          |   3 +-
>>>>   arch/loongarch/kernel/unwind.c          |  52 +++++++++
>>>>   arch/loongarch/kernel/unwind_guess.c    |  41 ++-----
>>>>   arch/loongarch/kernel/unwind_prologue.c | 135 
>>>> +++++++++---------------
>>>>   5 files changed, 135 insertions(+), 118 deletions(-)
>>>>   create mode 100644 arch/loongarch/kernel/unwind.c
>>>>
>>>> diff --git a/arch/loongarch/include/asm/unwind.h 
>>>> b/arch/loongarch/include/asm/unwind.h
>>>> index 6ece48f0ff77..a16aff1d086a 100644
>>>> --- a/arch/loongarch/include/asm/unwind.h
>>>> +++ b/arch/loongarch/include/asm/unwind.h
>>>> @@ -18,6 +18,8 @@ enum unwinder_type {
>>>>       UNWINDER_PROLOGUE,
>>>>   };
>>>>   +struct unwinder_ops;
>>>> +
>>>>   struct unwind_state {
>>>>       char type; /* UNWINDER_XXX */
>>>>       struct stack_info stack_info;
>>>> @@ -25,8 +27,22 @@ struct unwind_state {
>>>>       bool first, error, is_ftrace;
>>>>       int graph_idx;
>>>>       unsigned long sp, pc, ra;
>>>> +    const struct unwinder_ops *ops;
>>>> +};
>>>> +
>>>> +struct unwinder_ops {
>>>> +    void (*unwind_start)(struct unwind_state *state,
>>>> +                 struct task_struct *task, struct pt_regs *regs);
>>>> +    bool (*unwind_next_frame)(struct unwind_state *state);
>>>> +    unsigned long (*unwind_get_return_address)(struct unwind_state 
>>>> *state);
>>>>   };
>>>>   +extern const struct unwinder_ops *default_unwinder;
>>>> +extern const struct unwinder_ops unwinder_guess;
>>>> +#ifdef CONFIG_UNWINDER_PROLOGUE
>>>> +extern const struct unwinder_ops unwinder_prologue;
>>>> +#endif
>>>> +
>>>>   void unwind_start(struct unwind_state *state,
>>>>             struct task_struct *task, struct pt_regs *regs);
>>>>   bool unwind_next_frame(struct unwind_state *state);
>>>> @@ -49,4 +65,10 @@ static inline unsigned long 
>>>> unwind_graph_addr(struct unwind_state *state,
>>>>       return ftrace_graph_ret_addr(state->task, &state->graph_idx,
>>>>                        pc, (unsigned long *)(cfa - 
>>>> GRAPH_FAKE_OFFSET));
>>>>   }
>>>> +
>>>> +static inline void unwind_register_unwinder(struct unwind_state 
>>>> *state,
>>>> +                      const struct unwinder_ops *unwinder)
>>>> +{
>>>> +    state->ops = unwinder;
>>>> +}
>>>>   #endif /* _ASM_UNWIND_H */
>>>> diff --git a/arch/loongarch/kernel/Makefile 
>>>> b/arch/loongarch/kernel/Makefile
>>>> index 7ca65195f7f8..cb6029ea3ea9 100644
>>>> --- a/arch/loongarch/kernel/Makefile
>>>> +++ b/arch/loongarch/kernel/Makefile
>>>> @@ -8,7 +8,7 @@ extra-y        := vmlinux.lds
>>>>   obj-y        += head.o cpu-probe.o cacheinfo.o env.o setup.o 
>>>> entry.o genex.o \
>>>>              traps.o irq.o idle.o process.o dma.o mem.o io.o 
>>>> reset.o switch.o \
>>>>              elf.o syscall.o signal.o time.o topology.o inst.o 
>>>> ptrace.o vdso.o \
>>>> -           alternative.o unaligned.o
>>>> +           alternative.o unaligned.o unwind.o unwind_guess.o
>>>>     obj-$(CONFIG_ACPI)        += acpi.o
>>>>   obj-$(CONFIG_EFI)         += efi.o
>>>> @@ -42,7 +42,6 @@ obj-$(CONFIG_MAGIC_SYSRQ)    += sysrq.o
>>>>   obj-$(CONFIG_KEXEC)        += machine_kexec.o relocate_kernel.o
>>>>   obj-$(CONFIG_CRASH_DUMP)    += crash_dump.o
>>>>   -obj-$(CONFIG_UNWINDER_GUESS)    += unwind_guess.o
>>>>   obj-$(CONFIG_UNWINDER_PROLOGUE) += unwind_prologue.o
>>>>     obj-$(CONFIG_PERF_EVENTS)    += perf_event.o perf_regs.o
>>>> diff --git a/arch/loongarch/kernel/unwind.c 
>>>> b/arch/loongarch/kernel/unwind.c
>>>> new file mode 100644
>>>> index 000000000000..568c6fe707d1
>>>> --- /dev/null
>>>> +++ b/arch/loongarch/kernel/unwind.c
>>>> @@ -0,0 +1,52 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +/*
>>>> + * Copyright (C) 2022 Loongson Technology Corporation Limited
>>>> + */
>>>> +#include <asm/unwind.h>
>>>> +
>>>> +#if defined(CONFIG_UNWINDER_GUESS)
>>>> +const struct unwinder_ops *default_unwinder = &unwinder_guess;
>>>> +#elif defined(CONFIG_UNWINDER_PROLOGUE)
>>>> +const struct unwinder_ops *default_unwinder = &unwinder_prologue;
>>>> +#endif
>>>> +
>>>> +unsigned long unwind_get_return_address(struct unwind_state *state)
>>>> +{
>>>> +    if (!state->ops || unwind_done(state))
>>>> +        return 0;
>>>> +    return state->ops->unwind_get_return_address(state);
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(unwind_get_return_address);
>>>> +
>>>> +void unwind_start(struct unwind_state *state, struct task_struct 
>>>> *task,
>>>> +            struct pt_regs *regs)
>>>> +{
>>>> +    memset(state, 0, sizeof(*state));
>>>> +    unwind_register_unwinder(state, default_unwinder);
>>>> +    if (regs) {
>>>> +        state->sp = regs->regs[3];
>>>> +        state->pc = regs->csr_era;
>>>> +        state->ra = regs->regs[1];
>>>> +    } 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;
>>>> +    }
>>>> +    state->task = task;
>>>> +    get_stack_info(state->sp, state->task, &state->stack_info);
>>>> +    state->pc = unwind_graph_addr(state, state->pc, state->sp);
>
>  here. :)

The PC from branch 'task == current' is the RA of current frame. And the 
PC from branch 'regs' is regs->csr_era, which may be RA of frame where 
to get the regs->csr_era. They all may traced by function_graph. 
Ftrace_graph_ret_addr() returns orignal addr and not destroys result, if 
the addr was not traced, so calling it for deal with above cases.

Thanks,

Jinyang

>
>>>> + state->ops->unwind_start(state, task, regs);
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(unwind_start);
>>>> +
>>>> +bool unwind_next_frame(struct unwind_state *state)
>>>> +{
>>>> +    if (!state->ops || unwind_done(state))
>>>> +        return false;
>>>> +    return state->ops->unwind_next_frame(state);
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(unwind_next_frame);
>>>> diff --git a/arch/loongarch/kernel/unwind_guess.c 
>>>> b/arch/loongarch/kernel/unwind_guess.c
>>>> index 8ce32c37c587..b7ca2b88ac63 100644
>>>> --- a/arch/loongarch/kernel/unwind_guess.c
>>>> +++ b/arch/loongarch/kernel/unwind_guess.c
>>>> @@ -7,51 +7,23 @@
>>>>     #include <asm/unwind.h>
>>>>   -unsigned long unwind_get_return_address(struct unwind_state *state)
>>>> +static unsigned long get_return_address(struct unwind_state *state)
>>>>   {
>>>> -    if (unwind_done(state))
>>>> -        return 0;
>>>>       return state->pc;
>>>>   }
>>>> -EXPORT_SYMBOL_GPL(unwind_get_return_address);
>>>>   -void unwind_start(struct unwind_state *state, struct task_struct 
>>>> *task,
>>>> +static void start(struct unwind_state *state, struct task_struct 
>>>> *task,
>>>>               struct pt_regs *regs)
>>>>   {
>>>> -    memset(state, 0, sizeof(*state));
>>>> -
>>>> -    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);
>>>> -    }
>>>> -
>>>> -    state->task = task;
>>>> -    state->first = true;
>>>> -    state->pc = unwind_graph_add(state, state->pc, state->sp);
>>>
>>> Do we need to unwind_graph_add again here? unwinder_guess and 
>>> unwind_prologue have already been done.
>>
>> Hi, Qing
>>
>>
>> Sorry I don't what meanning here, as here is a delete line.
>>
> Sorry, It's the unwind_start up here.
>>
>>>
>>>> -    get_stack_info(state->sp, state->task, &state->stack_info);
>>>> -
>>>>       if (!unwind_done(state) && !__kernel_text_address(state->pc))
>>>>           unwind_next_frame(state);
>>>>   }
>>>> -EXPORT_SYMBOL_GPL(unwind_start);
>>>>   -bool unwind_next_frame(struct unwind_state *state)
>>>> +static bool next_frame(struct unwind_state *state)
>>>>   {
>>>>       struct stack_info *info = &state->stack_info;
>>>>       unsigned long addr;
>>>>   -    if (unwind_done(state))
>>>> -        return false;
>>>> -
>>>> -    if (state->first)
>>>> -        state->first = false;
>>>> -
>>>>       do {
>>>>           for (state->sp += sizeof(unsigned long);
>>>>                state->sp < info->end;
>>>> @@ -68,4 +40,9 @@ bool unwind_next_frame(struct unwind_state *state)
>>>>         return false;
>>>>   }
>>>> -EXPORT_SYMBOL_GPL(unwind_next_frame);
>>>> +
>>>> +const struct unwinder_ops unwinder_guess = {
>>>> +    .unwind_start = start,
>>>> +    .unwind_next_frame = next_frame,
>>>> +    .unwind_get_return_address = get_return_address,
>>>> +};
>>>> diff --git a/arch/loongarch/kernel/unwind_prologue.c 
>>>> b/arch/loongarch/kernel/unwind_prologue.c
>>>> index d464c533c64f..9677e13c4b4c 100644
>>>> --- a/arch/loongarch/kernel/unwind_prologue.c
>>>> +++ b/arch/loongarch/kernel/unwind_prologue.c
>>>> @@ -9,6 +9,8 @@
>>>>   #include <asm/ptrace.h>
>>>>   #include <asm/unwind.h>
>>>>   +static const struct unwinder_ops *guard_unwinder = &unwinder_guess;
>>>> +
>>>>   static inline void unwind_state_fixup(struct unwind_state *state)
>>>>   {
>>>>   #ifdef CONFIG_DYNAMIC_FTRACE
>>>> @@ -19,31 +21,19 @@ static inline void unwind_state_fixup(struct 
>>>> unwind_state *state)
>>>>   #endif
>>>>   }
>>>>   -unsigned long unwind_get_return_address(struct unwind_state *state)
>>>> +static unsigned long get_return_address(struct unwind_state *state)
>>>>   {
>>>> -    if (unwind_done(state))
>>>> -        return 0;
>>>>       return state->pc;
>>>>   }
>>>> -EXPORT_SYMBOL_GPL(unwind_get_return_address);
>>>> -
>>>> -static bool unwind_by_guess(struct unwind_state *state)
>>>> -{
>>>> -    struct stack_info *info = &state->stack_info;
>>>> -    unsigned long addr;
>>>> -
>>>> -    for (state->sp += sizeof(unsigned long);
>>>> -         state->sp < info->end;
>>>> -         state->sp += sizeof(unsigned long)) {
>>>> -        addr = *(unsigned long *)(state->sp);
>>>> -        state->pc = unwind_graph_addr(state, addr, state->sp + 8);
>>>> -        if (__kernel_text_address(state->pc))
>>>> -            return true;
>>>> -    }
>>>> -
>>>> -    return false;
>>>> -}
>>>>   +/*
>>>> + * LoongArch function prologue like follows,
>>>> + *     [others instructions not use stack var]
>>>> + *     addi.d sp, sp, -imm
>>>> + *     st.d   xx, sp, offset <- save callee saved regs and
>>>> + *     st.d   yy, sp, offset    save ra if function is nest.
>>>> + *     [others instructions]
>>>> + */
>>>>   static bool unwind_by_prologue(struct unwind_state *state)
>>>>   {
>>>>       long frame_ra = -1;
>>>> @@ -89,6 +79,10 @@ static bool unwind_by_prologue(struct 
>>>> unwind_state *state)
>>>>           ip++;
>>>>       }
>>>>   +    /*
>>>> +     * Not find stack alloc action, PC may be in a leaf function. 
>>>> Only the
>>>> +     * first being true is reasonable, otherwise indicate analysis 
>>>> is broken.
>>>> +     */
>>>>       if (!frame_size) {
>>>>           if (state->first)
>>>>               goto first;
>>>> @@ -106,6 +100,7 @@ static bool unwind_by_prologue(struct 
>>>> unwind_state *state)
>>>>           ip++;
>>>>       }
>>>>   +    /* Not find save $ra action, PC may be in a leaf function, 
>>>> too. */
>>>>       if (frame_ra < 0) {
>>>>           if (state->first) {
>>>>               state->sp = state->sp + frame_size;
>>>> @@ -114,96 +109,63 @@ static bool unwind_by_prologue(struct 
>>>> unwind_state *state)
>>>>           return false;
>>>>       }
>>>>   -    if (state->first)
>>>> -        state->first = false;
>>>> -
>>>>       state->pc = *(unsigned long *)(state->sp + frame_ra);
>>>>       state->sp = state->sp + frame_size;
>>>>       goto out;
>>>>     first:
>>>> -    state->first = false;
>>>> -    if (state->pc == state->ra)
>>>> -        return false;
>>>> -
>>>>       state->pc = state->ra;
>>>>     out:
>>>> +    state->first = false;
>>>>       unwind_state_fixup(state);
>>>>       return !!__kernel_text_address(state->pc);
>>>>   }
>>>>   -void unwind_start(struct unwind_state *state, struct task_struct 
>>>> *task,
>>>> +static void start(struct unwind_state *state, struct task_struct 
>>>> *task,
>>>>               struct pt_regs *regs)
>>>>   {
>>>> -    memset(state, 0, sizeof(*state));
>>>> -    state->type = UNWINDER_PROLOGUE;
>>>> -
>>>> -    if (regs) {
>>>> -        state->sp = regs->regs[3];
>>>> -        state->pc = regs->csr_era;
>>>> -        state->ra = regs->regs[1];
>>>> -        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;
>>>> -    }
>>>> -
>>>> -    state->task = task;
>>>>       state->first = true;
>>>> -    state->pc = unwind_graph_addr(state, state->pc, state->sp);
>>>> -    get_stack_info(state->sp, state->task, &state->stack_info);
>>>>   -    if (!unwind_done(state) && !__kernel_text_address(state->pc))
>>>> -        unwind_next_frame(state);
>>>> +    /*
>>>> +     * The current PC is not kernel text address, we cannot find its
>>>> +     * relative symbol. Thus, prologue analysis will be broken. 
>>>> Luckly,
>>>> +     * we can use the guard unwinder.
>>>> +     */
>>>> +    if (!__kernel_text_address(state->pc)) {
>>>> +        unwind_register_unwinder(state, guard_unwinder);
>>>
>>> Just add a comment here. Instead of using guard_unwinder, can we still
>>> use guess_unwinder?
>>
>> Yes, and I'll use '&guess_unwinder' in next version. And I'll
>> drop unwind type in next version, too.
>>
>>
>> Thanks,
>>
>> Jinyang
>>