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Message-ID: <e84aa8f0-3885-452c-9250-c5910d869263@zytor.com>
Date: Thu, 27 Jun 2024 09:45:34 -0700
From: Xin Li <xin@...or.com>
To: Nikolay Borisov <nik.borisov@...e.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, hpa@...or.com,
will@...nel.org, peterz@...radead.org, akpm@...ux-foundation.org,
acme@...nel.org, namhyung@...nel.org, brgerst@...il.com
Subject: Re: [PATCH v3 2/4] x86/cpufeatures: Generate a feature mask header
based on build config
On 6/26/2024 4:36 AM, Nikolay Borisov wrote:
>
>
> On 22.06.24 г. 20:14 ч., 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
>>
>> config X86_DISABLED_FEATURE_FRED
>> def_bool y
>> depends on !X86_FRED
>>
>> to arch/x86/Kconfig.cpufeatures, instead of adding a conditional CPU
>> feature disable flag, e.g., DISABLE_FRED.
>>
>> Lastly the generated required and disabled feature masks will be added
>> to their corresponding feature masks for this particular compile-time
>> configuration.
>>
>> [ Xin: build integration improvements ]
>>
>> Signed-off-by: H. Peter Anvin (Intel) <hpa@...or.com>
>> Signed-off-by: Xin Li (Intel) <xin@...or.com>
>
> Overall LGTM, some minor points below.
>
>
> Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>
Thanks!
>
>
> <snip>
>
>> diff --git a/arch/x86/tools/featuremasks.awk
>> b/arch/x86/tools/featuremasks.awk
>> new file mode 100755
>> index 000000000000..989b021e73d3
>> --- /dev/null
>> +++ b/arch/x86/tools/featuremasks.awk
>> @@ -0,0 +1,84 @@
>> +#!/usr/bin/awk
>> +#
>> +# Convert cpufeatures.h to a list of compile-time masks
>> +# Note: this blithly assumes that each word has at least one
>> +# feature defined in it; if not, something else is wrong!
>> +#
>> +
>> +BEGIN {
>> + printf "#ifndef _ASM_X86_FEATUREMASKS_H\n";
>> + printf "#define _ASM_X86_FEATUREMASKS_H\n\n";
>> +
>> + file = 0
>> +}
>> +
>> +BEGINFILE {
>> + switch (++file) {
>> + case 1: # cpufeatures.h
>> + FPAT = "#[ \t]*[a-z]+|[A-Za-z0-9_]+|[^ \t]";
>> + break;
>> + case 2: # .config
>> + FPAT = "CONFIG_[A-Z0-9_]+|is not set|[yn]";
>> + break;
>> + }
>> +}
>> +
>
> IMO this script could use a bit of high-level comments. Something like:
>
>
> # Create a dictionary of sorts, containing all defined feature bits
>> +file == 1 && $1 ~ /^#[ \t]*define$/ && $2 ~ /^X86_FEATURE_/ &&
>> +$3 == "(" && $5 == "*" && $7 == "+" && $9 == ")" {
>> + nfeat = $4 * $6 + $8;
>> + feat = $2;
>> + sub(/^X86_FEATURE_/, "", feat);
>> + feats[nfeat] = feat;
>> +}
>
>> +file == 1 && $1 ~ /^#[ \t]*define$/ && $2 == "NCAPINTS" {
>> + ncapints = strtonum($3);
>> +}
>> +
>
> # Create a dictionary featstat[REQUIRED|DISABLED, FEATURE_NAME] = on | off
>
>> +file == 2 && $1 ~ /^CONFIG_X86_[A-Z]*_FEATURE_/ {
>> + on = ($2 == "y");
>> + if (split($1, fs, "CONFIG_X86_|_FEATURE_") == 3)
>> + featstat[fs[2], fs[3]] = on;
>> +}
>> +
>> +END {
>> + sets[1] = "REQUIRED";
>> + sets[2] = "DISABLED";
>> +
>> + for (ns in sets) {
>> + s = sets[ns];
>> +
>> + printf "/*\n";
>> + printf " * %s features:\n", s;
>> + printf " *\n";
>> + fstr = "";
>> + for (i = 0; i < ncapints; i++) {
>> + mask = 0;
>> + for (j = 0; j < 32; j++) {
>> + nfeat = i*32 + j;
>> + feat = feats[nfeat];
>> + if (feat) {
>> + st = !!featstat[s, feat];
>> + if (st) {
>> + nfstr = fstr " " feat;
>> + if (length(nfstr) > 72) {
>> + printf " * %s\n", fstr;
>> + nfstr = " " feat;
>> + }
>> + fstr = nfstr;
>> + }
>> + mask += st * (2 ^ j);
>
> nit: This expression can be changed to mask += (2 ^j) and moved inside
> the 'if (st)' branch. Essentially only add a bit iff that status of the
> relevant feature in the kconfig is y, which is signified by the value of
> 'st' variable.
I will do a polish and send v4.
>
>> + }
>> + }
>> + masks[i] = mask;
>> + }
>> + printf " * %s\n */\n\n", fstr;
>> +
>> + for (i = 0; i < ncapints; i++) {
>> + printf "#define %s_MASK%d\t0x%08x\n", s, i, masks[i];
I should append 'U' here too.
>> + }
>> +
>> + printf "#define %s_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS !=
>> %d)\n\n", s, ncapints;
>> + }
>> +
>> + printf "#endif /* _ASM_X86_FEATUREMASKS_H */\n";
>> +}
>
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