linux-kernel - Re: [RESEND v1 2/3] x86/cpufeatures: Generate a feature mask header based on build config

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Message-ID: <99208d95-d3de-44d0-8b08-f508759aabca@zytor.com>
Date: Sun, 16 Jun 2024 00:26:48 -0700
From: Xin Li <xin@...or.com>
To: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Cc: tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        will@...nel.org, peterz@...radead.org, akpm@...ux-foundation.org,
        acme@...nel.org, namhyung@...nel.org
Subject: Re: [RESEND v1 2/3] x86/cpufeatures: Generate a feature mask header
 based on build config

On 5/9/2024 1:53 PM, Xin Li (Intel) wrote:
> From: "H. Peter Anvin (Intel)" <hpa@...or.com>
> 
> Introduce an AWK script to auto-generate a header with required and
> disabled feature masks based on <asm/cpufeatures.h> and current build
> config. Thus for any CPU feature with a build config, e.g., X86_FRED,
> simply add

...

> +
> +		printf "\n#define %s_MASKS ", s;
> +		pfx = "{";
> +		for (i = 0; i < ncapints; i++) {
> +			printf "%s \\\n\t%s_MASK_%d", pfx, s, i;
> +			pfx = ",";
> +		}
> +		printf " \\\n}\n\n";
> +
> +		printf "#define %s_FEATURE(x) \\\n", s;
> +		printf "\t((( ";
> +		for (i = 0; i < ncapints; i++) {
> +			if (masks[i]) {
> +				printf "\\\n\t\t((x) >> 5) == %2d ? %s_MASK%-3d : ", i, s, i;
> +			}
> +		}
> +		printf "0 \\\n";
> +		printf "\t) >> ((x) & 31)) & 1)\n\n";

This code generates macros {REQUIRED,DISABLED}_FEATURE(x) to tell if a
CPU feature, e.g., X86_FEATURE_FRED, is a required or disabled feature
for this particular compile-time configuration.

But they are NOT currently used, so I prefer to remove them for now.

Thanks!
     Xin