linux-kernel - Re: [PATCH v4 1/2] x86/fred: Allow variable-sized event frame

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Message-ID: <8c803b78-b6be-425d-a747-85e4c69b4f3d@zytor.com>
Date: Mon, 12 May 2025 22:02:55 -0700
From: Xin Li <xin@...or.com>
To: Brian Gerst <brgerst@...il.com>, Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, luto@...nel.org, tglx@...utronix.de,
        mingo@...nel.org, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com
Subject: Re: [PATCH v4 1/2] x86/fred: Allow variable-sized event frame

On 5/12/2025 5:10 AM, Brian Gerst wrote:
> On Mon, May 12, 2025 at 5:30 AM Peter Zijlstra <peterz@...radead.org> wrote:
>>
>> On Sun, May 11, 2025 at 11:43:52PM -0700, Xin Li (Intel) wrote:
>>
>>
>>> -#define INIT_THREAD_INFO(tsk)                        \
>>> -{                                            \
>>> -     .flags          = 0,                    \
>>> +extern unsigned long __top_init_kernel_stack[];
>>> +
>>> +#define INIT_THREAD_INFO(tsk)                                                \
>>> +{                                                                    \
>>> +     .flags          = 0,                                            \
>>> +     .user_pt_regs   = (struct pt_regs *)__top_init_kernel_stack,    \
>>
>> Should that not have a -1 on or something?
> 
> No, that symbol already accounts for subtracting the size of pt_regs.

Thanks for your answer :)