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Message-ID: <CAAhV-H4hR-Xdk5EpakR9ft0J+V5qgPj5q2T=zjh1SHMnnHK1vw@mail.gmail.com>
Date: Mon, 1 Aug 2022 23:26:03 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: Qing Zhang <zhangqing@...ngson.cn>
Cc: WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev,
LKML <linux-kernel@...r.kernel.org>,
Jiaxun Yang <jiaxun.yang@...goat.com>,
Jinyang He <hejinyang@...ngson.cn>
Subject: Re: [PATCH 2/4] LoongArch: Add prologue unwinder support
Hi, Qing,
On Mon, Aug 1, 2022 at 8:17 PM Qing Zhang <zhangqing@...ngson.cn> wrote:
>
> It unwind the stack frame based on prologue code analyze.
> CONFIG_KALLSYMS is needed, at least the address and length
> of each function.
>
> Three stages when we do unwind,
> (1)unwind_start(), the prapare of unwinding, fill unwind_state.
> (2)unwind_done(), judge whether the unwind process is finished or not.
> (3)unwind_next_frame(), unwind the next frame.
>
> Dividing unwinder helps to add new unwinders in the future, eg:
> unwind_frame, unwind_orc .etc
>
> Signed-off-by: Qing Zhang <zhangqing@...ngson.cn>
> ---
> arch/loongarch/Kconfig.debug | 19 +++
> arch/loongarch/include/asm/inst.h | 52 +++++++
> arch/loongarch/include/asm/unwind.h | 8 ++
> arch/loongarch/kernel/Makefile | 1 +
> arch/loongarch/kernel/traps.c | 5 +
> arch/loongarch/kernel/unwind_prologue.c | 172 ++++++++++++++++++++++++
> 6 files changed, 257 insertions(+)
> create mode 100644 arch/loongarch/kernel/unwind_prologue.c
>
> diff --git a/arch/loongarch/Kconfig.debug b/arch/loongarch/Kconfig.debug
> index 68634d4fa27b..57cdbe0cfd98 100644
> --- a/arch/loongarch/Kconfig.debug
> +++ b/arch/loongarch/Kconfig.debug
> @@ -1,3 +1,11 @@
> +choice
> + prompt "Choose kernel unwinder"
> + default UNWINDER_PROLOGUE if KALLSYMS
> + help
> + This determines which method will be used for unwinding kernel stack
> + traces for panics, oopses, bugs, warnings, perf, /proc/<pid>/stack,
> + lockdep, and more.
> +
> config UNWINDER_GUESS
> bool "Guess unwinder"
> help
> @@ -7,3 +15,14 @@ config UNWINDER_GUESS
>
> While this option often produces false positives, it can still be
> useful in many cases.
> +
> +config UNWINDER_PROLOGUE
> + bool "Prologue unwinder"
> + depends on KALLSYMS
> + help
> + This option enables the "prologue" unwinder for unwinding kernel stack
> + traces. It unwind the stack frame based on prologue code analyze. Symbol
> + information is needed, at least the address and length of each function.
> + Some of the addresses it reports may be incorrect.
> +
> +endchoice
> diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
> index 575d1bb66ffb..b876907ca65a 100644
> --- a/arch/loongarch/include/asm/inst.h
> +++ b/arch/loongarch/include/asm/inst.h
> @@ -23,12 +23,33 @@ enum reg1i20_op {
> lu32id_op = 0x0b,
> };
>
> +enum reg1i21_op {
> + beqz_op = 0x10,
> + bnez_op = 0x11,
> +};
> +
> enum reg2i12_op {
> + addiw_op = 0x0a,
> + addid_op = 0x0b,
> lu52id_op = 0x0c,
> + ldb_op = 0xa0,
> + ldh_op = 0xa1,
> + ldw_op = 0xa2,
> + ldd_op = 0xa3,
> + stb_op = 0xa4,
> + sth_op = 0xa5,
> + stw_op = 0xa6,
> + std_op = 0xa7,
> };
>
> enum reg2i16_op {
> jirl_op = 0x13,
> + beq_op = 0x16,
> + bne_op = 0x17,
> + blt_op = 0x18,
> + bge_op = 0x19,
> + bltu_op = 0x1a,
> + bgeu_op = 0x1b,
> };
>
> struct reg0i26_format {
> @@ -110,6 +131,37 @@ enum loongarch_gpr {
> LOONGARCH_GPR_MAX
> };
>
> +#define is_imm12_negative(val) is_imm_negative(val, 12)
> +
> +static inline bool is_imm_negative(unsigned long val, unsigned int bit)
> +{
> + return val & (1UL << (bit - 1));
> +}
> +
> +static inline bool is_stack_alloc_ins(union loongarch_instruction *ip)
> +{
> + /* addi.d $sp, $sp, -imm */
> + return ip->reg2i12_format.opcode == addid_op &&
> + ip->reg2i12_format.rj == LOONGARCH_GPR_SP &&
> + ip->reg2i12_format.rd == LOONGARCH_GPR_SP &&
> + is_imm12_negative(ip->reg2i12_format.immediate);
> +}
> +
> +static inline bool is_ra_save_ins(union loongarch_instruction *ip)
> +{
> + /* st.d $ra, $sp, offset */
> + return ip->reg2i12_format.opcode == std_op &&
> + ip->reg2i12_format.rj == LOONGARCH_GPR_SP &&
> + ip->reg2i12_format.rd == LOONGARCH_GPR_RA &&
> + !is_imm12_negative(ip->reg2i12_format.immediate);
> +}
> +
> +static inline bool is_branch_insn(union loongarch_instruction insn)
> +{
> + return insn.reg1i21_format.opcode >= beqz_op &&
> + insn.reg1i21_format.opcode <= bgeu_op;
> +}
> +
> u32 larch_insn_gen_lu32id(enum loongarch_gpr rd, int imm);
> u32 larch_insn_gen_lu52id(enum loongarch_gpr rd, enum loongarch_gpr rj, int imm);
> u32 larch_insn_gen_jirl(enum loongarch_gpr rd, enum loongarch_gpr rj, unsigned long pc, unsigned long dest);
> diff --git a/arch/loongarch/include/asm/unwind.h b/arch/loongarch/include/asm/unwind.h
> index 243330b39d0d..f9f73a26504e 100644
> --- a/arch/loongarch/include/asm/unwind.h
> +++ b/arch/loongarch/include/asm/unwind.h
> @@ -14,6 +14,14 @@
> struct unwind_state {
> struct stack_info stack_info;
> struct task_struct *task;
> +#if defined(CONFIG_UNWINDER_PROLOGUE)
> + unsigned long ra;
> + bool enable;
> + /*
> + * Enable is the prologue analysis method
> + * otherwise is the way to guess.
> + */
> +#endif
> unsigned long sp, pc;
> bool first;
> bool error;
This data struct makes me very uncomfortable, especially "enable" and
the #ifdef, maybe we can rework it like this?
#define UNWINDER_GUESS 0
#define UNWINDER_PROLOGURE 1
struct unwind_state {
char type; /* UNWINDER_xxx */
bool first, error;
unsigned long sp, pc, ra;
struct task_struct *task;
struct stack_info stack_info;
};
Huacai
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index c5fa4adb23b6..918600e7b30f 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -23,5 +23,6 @@ obj-$(CONFIG_SMP) += smp.o
> obj-$(CONFIG_NUMA) += numa.o
>
> obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o
> +obj-$(CONFIG_UNWINDER_PROLOGUE) += unwind_prologue.o
>
> CPPFLAGS_vmlinux.lds := $(KBUILD_CFLAGS)
> diff --git a/arch/loongarch/kernel/traps.c b/arch/loongarch/kernel/traps.c
> index ef2c3aeb1dab..3e904fa12d48 100644
> --- a/arch/loongarch/kernel/traps.c
> +++ b/arch/loongarch/kernel/traps.c
> @@ -73,6 +73,11 @@ static void show_backtrace(struct task_struct *task, const struct pt_regs *regs,
>
> unwind_start(&state, task, pregs);
>
> +#ifdef CONFIG_UNWINDER_PROLOGUE
> + if (user_mode(regs))
> + state.enable = false;
> +#endif
> +
> printk("%sCall Trace:", loglvl);
> for (; !unwind_done(&state); unwind_next_frame(&state)) {
> addr = unwind_get_return_address(&state);
> diff --git a/arch/loongarch/kernel/unwind_prologue.c b/arch/loongarch/kernel/unwind_prologue.c
> new file mode 100644
> index 000000000000..072d1f7bf4ac
> --- /dev/null
> +++ b/arch/loongarch/kernel/unwind_prologue.c
> @@ -0,0 +1,172 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2022 Loongson Technology Corporation Limited
> + */
> +#include <linux/kallsyms.h>
> +
> +#include <asm/inst.h>
> +#include <asm/ptrace.h>
> +#include <asm/unwind.h>
> +
> +unsigned long unwind_get_return_address(struct unwind_state *state)
> +{
> +
> + if (unwind_done(state))
> + return 0;
> + else if (state->enable)
> + return state->pc;
> + else if (state->first)
> + return state->pc;
> +
> + return *(unsigned long *)(state->sp);
> +
> +}
> +EXPORT_SYMBOL_GPL(unwind_get_return_address);
> +
> +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;
> +
> + if (state->sp >= info->end || state->sp < info->begin)
> + return false;
> +
> + if (!kallsyms_lookup_size_offset(pc, &size, &offset))
> + return false;
> +
> + ip = (union loongarch_instruction *)(pc - offset);
> + ip_end = (union loongarch_instruction *)pc;
> +
> + while (ip < ip_end) {
> + if (is_stack_alloc_ins(ip)) {
> + frame_size = (1 << 12) - ip->reg2i12_format.immediate;
> + ip++;
> + break;
> + }
> + ip++;
> + }
> +
> + if (!frame_size) {
> + if (state->first)
> + goto first;
> +
> + return false;
> + }
> +
> + while (ip < ip_end) {
> + if (is_ra_save_ins(ip)) {
> + frame_ra = ip->reg2i12_format.immediate;
> + break;
> + }
> + if (is_branch_insn(*ip))
> + break;
> + ip++;
> + }
> +
> + if (frame_ra < 0) {
> + if (state->first) {
> + state->sp = state->sp + frame_size;
> + goto first;
> + }
> + return false;
> + }
> +
> + if (state->first)
> + state->first = false;
> +
> + state->pc = *(unsigned long *)(state->sp + frame_ra);
> + state->sp = state->sp + frame_size;
> + return !!__kernel_text_address(state->pc);
> +
> +first:
> + state->first = false;
> + if (state->pc == state->ra)
> + return false;
> +
> + state->pc = state->ra;
> +
> + return !!__kernel_text_address(state->ra);
> +}
> +
> +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);
> + if (__kernel_text_address(addr))
> + return true;
> + }
> +
> + return false;
> +}
> +
> +bool unwind_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 {
> + if (state->enable) {
> + if (unwind_by_prologue(state))
> + return true;
> +
> + 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;
> +
> + state->pc = pc;
> + state->sp = regs->regs[3];
> + state->ra = regs->regs[1];
> + state->first = true;
> + get_stack_info(state->sp, state->task, info);
> +
> + return true;
> + }
> + } else {
> + if (state->first)
> + state->first = false;
> + else if (unwind_by_guess(state))
> + return true;
> + }
> +
> + state->sp = info->next_sp;
> +
> + } while (!get_stack_info(state->sp, state->task, info));
> +
> + return false;
> +}
> +EXPORT_SYMBOL_GPL(unwind_next_frame);
> +
> +void unwind_start(struct unwind_state *state, struct task_struct *task,
> + struct pt_regs *regs)
> +{
> + memset(state, 0, sizeof(*state));
> +
> + if (__kernel_text_address(regs->csr_era))
> + state->enable = true;
> +
> + state->task = task;
> + state->pc = regs->csr_era;
> + state->sp = regs->regs[3];
> + state->ra = regs->regs[1];
> + state->first = true;
> +
> + 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);
> --
> 2.20.1
>
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