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

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Date:	Tue, 7 Jan 2014 09:49:46 +0100
From:	Jean Pihet <jean.pihet@...aro.org>
To:	Will Deacon <will.deacon@....com>
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 Will,

On 6 January 2014 19:30, Will Deacon <will.deacon@....com> wrote:
> Hi Jean,
>
> Thanks for the updated patches. One minor comment on this one.
Thanks for reviewing!

> 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?
Yes

I will resend an updated version asap.

>
> Will

Jean
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