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Message-ID: <b1d090e3-1d68-3508-9108-5d697fa84ddd@loongson.cn>
Date: Sat, 17 Dec 2022 09:47:45 +0800
From: Jinyang He <hejinyang@...ngson.cn>
To: Qing Zhang <zhangqing@...ngson.cn>,
Huacai Chen <chenhuacai@...nel.org>,
WANG Xuerui <kernel@...0n.name>
Cc: loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 4/6] LoongArch: Strip guess_unwinder out from
prologue_unwinder
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@...ngson.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
>>
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