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

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Date: Mon, 17 Jun 2024 06:46:28 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Xin Li <xin@...or.com>, 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, 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 June 16, 2024 12:26:48 AM PDT, Xin Li <xin@...or.com> wrote:
>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

The goal with these is that it can eliminate the handwritten code that tests a long list of masks. Again, automation.