linux-kernel - Re: [RFC PATCH v5 1/2] selftests/x86: add xsave test during and after signal handling

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Date:   Thu, 9 Dec 2021 10:22:42 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Pengfei Xu <pengfei.xu@...el.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        linux-kselftest <linux-kselftest@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Cc:     Heng Su <heng.su@...el.com>, Luck Tony <tony.luck@...el.com>,
        Mehta Sohil <sohil.mehta@...el.com>,
        Chen Yu C <yu.c.chen@...el.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [RFC PATCH v5 1/2] selftests/x86: add xsave test during and after
 signal handling

On 12/2/21 11:32 PM, Pengfei Xu wrote:
> +void populate_xstate_regs(void)
> +{
> +	set_fpu_reg();
> +	set_avx2_ymm();
> +	set_avx512_opmask();
> +	set_pkru_xstate();
> +}

Pengfei, as I mentioned several times, XMM and YMM registers are not
preserved across function calls.  This only works by chance.  The
compiler is free to clobber them at basically any time between when they
are populated and the XSAVE happens.