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SubjectRe: [PATCH v2 4/6] LoongArch: Strip guess_unwinder out from prologue_unwinder
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
>
>

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