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References: <20221229061516.31671-1-hejinyang@loongson.cn> <20221229061516.31671-5-hejinyang@loongson.cn>
In-Reply-To: <20221229061516.31671-5-hejinyang@loongson.cn>
From:   Huacai Chen <chenhuacai@kernel.org>
Date:   Sun, 1 Jan 2023 17:56:45 +0800
Message-ID: <CAAhV-H7J7yWpM-xLpK38gwEw3cMNU-BaxF3atVmDLyRxBcVrLg@mail.gmail.com>
Subject: Re: [PATCH v2 4/6] LoongArch: Strip guess_unwinder out from prologue_unwinder
To:     Jinyang He <hejinyang@loongson.cn>
Cc:     WANG Xuerui <kernel@xen0n.name>,
        Qing Zhang <zhangqing@loongson.cn>, 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>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi, Jinyang,

On Thu, Dec 29, 2022 at 2:15 PM Jinyang He <hejinyang@loongson.cn> 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     |  26 ++++-
>  arch/loongarch/kernel/Makefile          |   3 +-
>  arch/loongarch/kernel/traps.c           |   3 -
>  arch/loongarch/kernel/unwind.c          |  52 +++++++++
>  arch/loongarch/kernel/unwind_guess.c    |  41 ++------
>  arch/loongarch/kernel/unwind_prologue.c | 133 +++++++++---------------
>  6 files changed, 132 insertions(+), 126 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..4a55fd7b77ad 100644
> --- a/arch/loongarch/include/asm/unwind.h
> +++ b/arch/loongarch/include/asm/unwind.h
> @@ -13,20 +13,30 @@
>  #include <asm/ptrace.h>
>  #include <asm/stacktrace.h>
>
> -enum unwinder_type {
> -       UNWINDER_GUESS,
> -       UNWINDER_PROLOGUE,
> -};
> +struct unwinder_ops;
>
>  struct unwind_state {
> -       char type; /* UNWINDER_XXX */
>         struct stack_info stack_info;
>         struct task_struct *task;
>         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 +59,10 @@ 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
We do have CONFIG_UNWINDER_GUESS and I don't like to build guess
unwinder unconditionally, maybe we can refactor it to make the
unwinder still user selectable.

Huacai
>
>  obj-$(CONFIG_PERF_EVENTS)      += perf_event.o perf_regs.o
> diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
> index 3adc44832205..1ea14f6c18d3 100644
> --- a/arch/loongarch/kernel/traps.c
> +++ b/arch/loongarch/kernel/traps.c
> @@ -72,9 +72,6 @@ static void show_backtrace(struct task_struct *task, const struct pt_regs *regs,
>         if (!task)
>                 task = current;
>
> -       if (user_mode(regs))
> -               state.type = UNWINDER_GUESS;
> -
>         printk("%sCall Trace:", loglvl);
>         for (unwind_start(&state, task, pregs);
>               !unwind_done(&state); unwind_next_frame(&state)) {
> diff --git a/arch/loongarch/kernel/unwind.c b/arch/loongarch/kernel/unwind.c
> new file mode 100644
> index 000000000000..24d2cf99bfb6
> --- /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 || task == NULL) {
> +               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);
> +       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 935d24f8c95c..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 || task == NULL) {
> -               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_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);
>  }
> -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 f7994ed05f04..beb57ea24da2 100644
> --- a/arch/loongarch/kernel/unwind_prologue.c
> +++ b/arch/loongarch/kernel/unwind_prologue.c
> @@ -19,31 +19,19 @@ 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 +77,10 @@ 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 +98,7 @@ 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 +107,63 @@ 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 || task == NULL) {
> -               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 guess unwinder.
> +        */
> +       if (!__kernel_text_address(state->pc)) {
> +               unwind_register_unwinder(state, &unwinder_guess);
> +               if (!unwind_done(state))
> +                       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;
>         struct pt_regs *regs;
>         unsigned long pc;
>
> -       if (unwind_done(state))
> -               return false;
> -
>         do {
> -               switch (state->type) {
> -               case UNWINDER_GUESS:
> -                       state->first = false;
> -                       if (unwind_by_guess(state))
> -                               return true;
> -                       break;
> -
> -               case UNWINDER_PROLOGUE:
> -                       if (unwind_by_prologue(state)) {
> -                               state->pc = unwind_graph_addr(state, state->pc, state->sp);
> -                               return true;
> -                       }
> +               if (unwind_by_prologue(state)) {
> +                       state->pc = unwind_graph_addr(state, state->pc, state->sp);
> +                       return true;
> +               }
>
> -                       if (info->type == STACK_TYPE_IRQ &&
> -                               info->end == state->sp) {
> -                               regs = (struct pt_regs *)info->next_sp;
> -                               pc = regs->csr_era;
> +               if (info->type == STACK_TYPE_IRQ &&
> +                   info->end == state->sp) {
> +                       regs = (struct pt_regs *)info->next_sp;
> +                       pc = regs->csr_era;
>
> -                               if (user_mode(regs) || !__kernel_text_address(pc))
> -                                       return false;
> +                       if (user_mode(regs) || !__kernel_text_address(pc))
> +                               return false;
>
> -                               state->first = true;
> -                               state->ra = regs->regs[1];
> -                               state->sp = regs->regs[3];
> -                               state->pc = pc;
> -                               get_stack_info(state->sp, state->task, info);
> +                       state->first = true;
> +                       state->ra = regs->regs[1];
> +                       state->sp = regs->regs[3];
> +                       state->pc = pc;
> +                       get_stack_info(state->sp, state->task, info);
>
> -                               return true;
> -                       }
> +                       return true;
>                 }
>
>                 state->sp = info->next_sp;
> @@ -212,4 +172,9 @@ bool unwind_next_frame(struct unwind_state *state)
>
>         return false;
>  }
> -EXPORT_SYMBOL_GPL(unwind_next_frame);
> +
> +const struct unwinder_ops unwinder_prologue = {
> +       .unwind_start = start,
> +       .unwind_next_frame = next_frame,
> +       .unwind_get_return_address = get_return_address,
> +};
> --
> 2.34.3
>
>