linux-kernel - Re: [PATCH 1/3] ARM64: perf: add support for perf registers API

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Date:	Mon, 6 Jan 2014 18:30:01 +0000
From:	Will Deacon <will.deacon@....com>
To:	Jean Pihet <jean.pihet@...aro.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
	Arnaldo <acme@...stprotocols.net>,
	"patches@...aro.org" <patches@...aro.org>,
	Jean Pihet <jean.pihet@...oldbits.com>
Subject: Re: [PATCH 1/3] ARM64: perf: add support for perf registers API

Hi Jean,

Thanks for the updated patches. One minor comment on this one.

On Mon, Dec 30, 2013 at 04:25:30PM +0000, Jean Pihet wrote:
> From: Jean Pihet <jean.pihet@...oldbits.com>
> 
> This patch implements the functions required for the perf registers API,
> allowing the perf tool to interface kernel register dumps with libunwind
> in order to provide userspace backtracing.
> Compat mode is also supported.

[...]

> +u64 perf_reg_value(struct pt_regs *regs, int idx)
> +{
> +	if (WARN_ON_ONCE((u32)idx >= PERF_REG_ARM64_MAX))
> +		return 0;

While this is probably fine, I'd feel more comfortable if you had separate
limit checks for native and compat...

> +	/*
> +	 * Compat (i.e. 32 bit) mode:
> +	 * - PC has been set in the pt_regs struct in kernel_entry,
> +	 * - Handle SP and LR here.
> +	 */
> +	if (compat_user_mode(regs)) {

i.e. have a WARN_ON_ONCE here for the compat structure size.

> +		if ((u32)idx == PERF_REG_ARM64_SP)
> +			return regs->compat_sp;
> +		if ((u32)idx == PERF_REG_ARM64_LR)
> +			return regs->compat_lr;
> +	}

then stick an else here with the original check.

Make sense?

Will
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