linux-kernel - Re: [PATCH v4 19/39] unwind_user/sframe: Add support for reading .sframe contents

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Message-ID: <20250204194250.ihfn2iynpwckzjnn@jpoimboe>
Date: Tue, 4 Feb 2025 11:42:50 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Weinan Liu <wnliu@...gle.com>
Cc: acme@...nel.org, adrian.hunter@...el.com,
	alexander.shishkin@...ux.intel.com, andrii.nakryiko@...il.com,
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Subject: Re: [PATCH v4 19/39] unwind_user/sframe: Add support for reading
 .sframe contents

On Thu, Jan 30, 2025 at 07:51:15PM +0000, Weinan Liu wrote:
> Nit: swap() might be a simplify way to alternate pointers between two
> fre_addr[] entries.
> 
> For example,
> 
> static __always_inline int __find_fre(struct sframe_section *sec,
> 				      struct sframe_fde *fde, unsigned long ip,
> 				      struct unwind_user_frame *frame)
> {
> 	/* intialize fres[] with invalid value */
> 	struct sframe_fre fres[2] = {0};
> 	struct sframe_fre *fre = &fres[1], *prev_fre = fres;
> 
> 	for (i = 0; i < fde->fres_num; i++) {
> 		swap(fre, next_fre);
> 		ret = __read_fre(sec, fde, fre_addr, fre);

Problem is, if it breaks out early here on the first iteration:

> 		if (fre->ip_off > ip_off)
> 			break;
> 	}
> 
> 	if (fre->size == 0)
> 		return -EINVAL;

Then fre isn't valid even though it has a nonzero size.

-- 
Josh