linux-kernel - Re: [PATCH v3 09/19] unwind: Introduce sframe user space unwinding

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Message-ID: <20241107082502.4060233-1-wnliu@google.com>
Date: Thu,  7 Nov 2024 08:25:02 +0000
From: Weinan Liu <wnliu@...gle.com>
To: jpoimboe@...nel.org
Cc: acme@...nel.org, adrian.hunter@...el.com, 
	alexander.shishkin@...ux.intel.com, andrii.nakryiko@...il.com, 
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	mingo@...nel.org, namhyung@...nel.org, peterz@...radead.org, 
	rostedt@...dmis.org, sam@...too.org, x86@...nel.org
Subject: Re: [PATCH v3 09/19] unwind: Introduce sframe user space unwinding

> diff --git a/kernel/unwind/sframe.c b/kernel/unwind/sframe.c
...
> +static int find_fre(struct sframe_section *sec, struct sframe_fde *fde,
> +		    unsigned long ip, struct unwind_user_frame *frame)
> +{
> +	unsigned char fde_type = SFRAME_FUNC_FDE_TYPE(fde->info);
> +	unsigned char fre_type = SFRAME_FUNC_FRE_TYPE(fde->info);
> +	unsigned char offset_count, offset_size;
> +	s32 cfa_off, ra_off, fp_off, ip_off;
> +	void __user *f, *last_f = NULL;
> +	unsigned char addr_size;
> +	u32 last_fre_ip_off = 0;
> +	u8 fre_info = 0;
> +	int i;
> +
> +	addr_size = fre_type_to_size(fre_type);
> +	if (!addr_size)
> +		return -EINVAL;
> +
> +	ip_off = ip - (sec->sframe_addr + fde->start_addr);

nit: Since we already know wether the ip_off should mask or not, I think we don't have to check fde_type and mask the ip_off everytime.
	ip_off = (fde_type == SFRAME_FDE_TYPE_PCINC) ? ip_off : ip_off % fde->rep_size;

> +
> +	f = (void __user *)sec->fres_addr + fde->fres_off;
> +
> +	for (i = 0; i < fde->fres_num; i++) {
> +		u32 fre_ip_off;
> +
> +		SFRAME_GET_USER(fre_ip_off, f, addr_size);
> +
> +		if (fre_ip_off < last_fre_ip_off)
> +			return -EINVAL;
> +
> +		last_fre_ip_off = fre_ip_off;
> +
> +		if (fde_type == SFRAME_FDE_TYPE_PCINC) {
> +			if (ip_off < fre_ip_off)
> +				break;
> +		} else {
> +			/* SFRAME_FDE_TYPE_PCMASK */
> +			if (ip_off % fde->rep_size < fre_ip_off)
> +				break;
> +		}
> +
> +		SFRAME_GET_USER(fre_info, f, 1);
> +
> +		offset_count = SFRAME_FRE_OFFSET_COUNT(fre_info);
> +		offset_size  = offset_size_enum_to_size(SFRAME_FRE_OFFSET_SIZE(fre_info));
> +
> +		if (!offset_count || !offset_size)
> +			return -EINVAL;
> +
> +		last_f = f;
> +		f += offset_count * offset_size;
> +	}
> +
> +	if (!last_f)
> +		return -EINVAL;
> +
> +	f = last_f;
> +
> +	SFRAME_GET_USER(cfa_off, f, offset_size);
> +	offset_count--;
> +
> +	ra_off = sec->ra_off;
> +	if (!ra_off) {
> +		if (!offset_count--)
> +			return -EINVAL;
> +
> +		SFRAME_GET_USER(ra_off, f, offset_size);
> +	}
> +
> +	fp_off = sec->fp_off;
> +	if (!fp_off && offset_count) {
> +		offset_count--;
> +		SFRAME_GET_USER(fp_off, f, offset_size);
> +	}
> +
> +	if (offset_count)
> +		return -EINVAL;
> +
> +	frame->cfa_off = cfa_off;
> +	frame->ra_off = ra_off;
> +	frame->fp_off = fp_off;
> +	frame->use_fp = SFRAME_FRE_CFA_BASE_REG_ID(fre_info) == SFRAME_BASE_REG_FP;
> +
> +	return 0;
> +}