linux-kernel - Re: [PATCH 2/3] LoongArch: Add prologue unwinder support

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Message-ID: <ddddff68-cae3-24e7-d0b7-d08abc94baf2@loongson.cn>
Date:   Fri, 29 Jul 2022 10:14:44 +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,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH 2/3] LoongArch: Add prologue unwinder support

Hi, Qing,


On 07/28/2022 10:05 PM, Qing Zhang 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>
>
>   
> +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 &&
> +		ip->reg2i12_format.immediate & (1 << 11);
Checking the sign bit can be used in other place.
> +}
> +
> +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;
> +}
> +
> +static inline bool is_branch_insn(union loongarch_instruction insn)
Does it by using pointer parameter as above functions do.
> +{
> +	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..09394e536ea9 100644
> --- a/arch/loongarch/include/asm/unwind.h
> +++ b/arch/loongarch/include/asm/unwind.h
> @@ -14,6 +14,10 @@
>   struct unwind_state {
>   	struct stack_info stack_info;
>   	struct task_struct *task;
> +#if defined(CONFIG_UNWINDER_PROLOGUE)
> +	unsigned long ra;
> +	bool enable;
Annotating here is appreciating. Enable is the way of prologue analysis
while !enable is the way of guess.
> +#endif
>   	unsigned long sp, pc;
>   	bool first;
>   	bool error;
[...]
> +
> +unsigned long unwind_get_return_address(struct unwind_state *state)
> +{
> +
> +	if (unwind_done(state))
> +		return 0;
> +
> +	if (state->enable)
> +		return state->pc;
> +	else if (state->first)
> +		return state->pc;
Combine conditions.
> +
> +	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;
Due to there will be other place convert unsigned to signed, we have
a chance that create a inline function in inst.h. Do it as same as
checking the sign bit.

> +			ip++;
> +			break;
> +		}
> +		ip++;
> +	}
> +
[...]
> +
> +	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;
> +
> +			if (unwind_by_guess(state))
> +				return true;
> +		}
I'd prefer separate the block of 'if...else...' into two inline
functions, that makes codes clear.

Thanks,
Jinyang