Re: [PATCH v6 3/5] x86/cpufeatures: Generate a feature mask header based on build config

From: H. Peter Anvin
Date: Mon Mar 03 2025 - 07:07:00 EST

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In reply to: Aithal, Srikanth: "Re: [PATCH v6 3/5] x86/cpufeatures: Generate a feature mask header based on build config"
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On March 3, 2025 3:38:05 AM PST, "Aithal, Srikanth" <sraithal@xxxxxxx> wrote:
>On 2/28/2025 1:53 PM, Xin Li (Intel) wrote:
>> From: "H. Peter Anvin (Intel)" <hpa@xxxxxxxxx>
>>
>> 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@xxxxxxxxx>
>> Signed-off-by: Xin Li (Intel) <xin@xxxxxxxxx>
>> Reviewed-by: Nikolay Borisov <nik.borisov@xxxxxxxx>
>> ---
>>
>> Change in v6:
>> * Make the AWK script work for mawk and BusyBox awk (Borislav Petkov).
>>
>> Change in v5:
>> * More polishes (Nikolay Borisov).
>>
>> Changes in v4:
>> * Add a few high-level comments to the AWK script (Nikolay Borisov).
>> * Enforce CPU feature mask values to be unsigned.
>>
>> Changes in v3:
>> * Remove AWK code that generates extra debugging comments (Brian Gerst).
>> * Move SSE_MASK to verify_cpu.S, the only place it is used (Brian Gerst).
>>
>> Change in v2:
>> * Remove code generating unused 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.
>> ---
>> arch/x86/Makefile | 17 ++++++-
>> arch/x86/boot/cpucheck.c | 3 +-
>> arch/x86/boot/cpuflags.c | 1 -
>> arch/x86/boot/mkcpustr.c | 3 +-
>> arch/x86/include/asm/Kbuild | 1 +
>> arch/x86/include/asm/cpufeature.h | 1 +
>> arch/x86/include/asm/cpufeatures.h | 8 ---
>> arch/x86/kernel/verify_cpu.S | 4 ++
>> arch/x86/tools/featuremasks.awk | 81 ++++++++++++++++++++++++++++++
>> 9 files changed, 105 insertions(+), 14 deletions(-)
>> create mode 100755 arch/x86/tools/featuremasks.awk
>>
>> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
>> index 6784129328f6..60583987d320 100644
>> --- a/arch/x86/Makefile
>> +++ b/arch/x86/Makefile
>> @@ -263,9 +263,22 @@ archscripts: scripts_basic
>> $(Q)$(MAKE) $(build)=arch/x86/tools relocs
>> ###
>> -# Syscall table generation
>> +# Feature masks header and syscall table generation
>> -archheaders:
>> +out := arch/x86/include/generated/asm
>> +featuremasks_hdr := featuremasks.h
>> +featuremasks_awk := $(srctree)/arch/x86/tools/featuremasks.awk
>> +cpufeatures_hdr := $(srctree)/arch/x86/include/asm/cpufeatures.h
>> +quiet_cmd_gen_featuremasks = GEN $@
>> + cmd_gen_featuremasks = $(AWK) -f $(featuremasks_awk) $(cpufeatures_hdr) $(KCONFIG_CONFIG) > $@
>> +
>> +$(out)/$(featuremasks_hdr): $(featuremasks_awk) $(cpufeatures_hdr) $(KCONFIG_CONFIG) FORCE
>> + $(shell mkdir -p $(out))
>> + $(call if_changed,gen_featuremasks)
>> +
>> +targets += $(out)/$(featuremasks_hdr)
>> +
>> +archheaders: $(out)/$(featuremasks_hdr)
>> $(Q)$(MAKE) $(build)=arch/x86/entry/syscalls all
>> ###
>> diff --git a/arch/x86/boot/cpucheck.c b/arch/x86/boot/cpucheck.c
>> index 0aae4d4ed615..8d03a741d1b2 100644
>> --- a/arch/x86/boot/cpucheck.c
>> +++ b/arch/x86/boot/cpucheck.c
>> @@ -22,10 +22,11 @@
>> # include "boot.h"
>> #endif
>> #include <linux/types.h>
>> +#include <asm/featuremasks.h>
>> #include <asm/intel-family.h>
>> #include <asm/processor-flags.h>
>> -#include <asm/required-features.h>
>> #include <asm/msr-index.h>
>> +
>> #include "string.h"
>> #include "msr.h"
>> diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
>> index d75237ba7ce9..0cabdacb2a2f 100644
>> --- a/arch/x86/boot/cpuflags.c
>> +++ b/arch/x86/boot/cpuflags.c
>> @@ -3,7 +3,6 @@
>> #include "bitops.h"
>> #include <asm/processor-flags.h>
>> -#include <asm/required-features.h>
>> #include <asm/msr-index.h>
>> #include "cpuflags.h"
>> diff --git a/arch/x86/boot/mkcpustr.c b/arch/x86/boot/mkcpustr.c
>> index da0ccc5de538..b90110109675 100644
>> --- a/arch/x86/boot/mkcpustr.c
>> +++ b/arch/x86/boot/mkcpustr.c
>> @@ -12,8 +12,6 @@
>> #include <stdio.h>
>> -#include "../include/asm/required-features.h"
>> -#include "../include/asm/disabled-features.h"
>> #include "../include/asm/cpufeatures.h"
>> #include "../include/asm/vmxfeatures.h"
>> #include "../kernel/cpu/capflags.c"
>> @@ -23,6 +21,7 @@ int main(void)
>> int i, j;
>> const char *str;
>> + printf("#include <asm/featuremasks.h>\n\n");
>> printf("static const char x86_cap_strs[] =\n");
>> for (i = 0; i < NCAPINTS; i++) {
>> diff --git a/arch/x86/include/asm/Kbuild b/arch/x86/include/asm/Kbuild
>> index 58f4ddecc5fa..51022d21003e 100644
>> --- a/arch/x86/include/asm/Kbuild
>> +++ b/arch/x86/include/asm/Kbuild
>> @@ -8,6 +8,7 @@ generated-y += syscalls_x32.h
>> generated-y += unistd_32_ia32.h
>> generated-y += unistd_64_x32.h
>> generated-y += xen-hypercalls.h
>> +generated-y += featuremasks.h
>> generic-y += early_ioremap.h
>> generic-y += fprobe.h
>> diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
>> index de1ad09fe8d7..077a5bbd1cc5 100644
>> --- a/arch/x86/include/asm/cpufeature.h
>> +++ b/arch/x86/include/asm/cpufeature.h
>> @@ -9,6 +9,7 @@
>> #include <asm/asm.h>
>> #include <linux/bitops.h>
>> #include <asm/alternative.h>
>> +#include <asm/featuremasks.h>
>> enum cpuid_leafs
>> {
>> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
>> index c8701abb7752..b9b7329f4ac4 100644
>> --- a/arch/x86/include/asm/cpufeatures.h
>> +++ b/arch/x86/include/asm/cpufeatures.h
>> @@ -2,14 +2,6 @@
>> #ifndef _ASM_X86_CPUFEATURES_H
>> #define _ASM_X86_CPUFEATURES_H
>> -#ifndef _ASM_X86_REQUIRED_FEATURES_H
>> -#include <asm/required-features.h>
>> -#endif
>> -
>> -#ifndef _ASM_X86_DISABLED_FEATURES_H
>> -#include <asm/disabled-features.h>
>> -#endif
>> -
>> /*
>> * Defines x86 CPU feature bits
>> */
>> diff --git a/arch/x86/kernel/verify_cpu.S b/arch/x86/kernel/verify_cpu.S
>> index 1258a5872d12..a23a65d5d177 100644
>> --- a/arch/x86/kernel/verify_cpu.S
>> +++ b/arch/x86/kernel/verify_cpu.S
>> @@ -29,8 +29,12 @@
>> */
>> #include <asm/cpufeatures.h>
>> +#include <asm/featuremasks.h>
>> #include <asm/msr-index.h>
>> +#define SSE_MASK \
>> + (REQUIRED_MASK0 & ((1<<(X86_FEATURE_XMM & 31)) | (1<<(X86_FEATURE_XMM2 & 31))))
>> +
>> SYM_FUNC_START_LOCAL(verify_cpu)
>> pushf # Save caller passed flags
>> push $0 # Kill any dangerous flags
>> diff --git a/arch/x86/tools/featuremasks.awk b/arch/x86/tools/featuremasks.awk
>> new file mode 100755
>> index 000000000000..fd3e72147157
>> --- /dev/null
>> +++ b/arch/x86/tools/featuremasks.awk
>> @@ -0,0 +1,81 @@
>> +#!/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
>> +}
>> +
>> +FNR == 1 {
>> + ++file;
>> +
>> + # arch/x86/include/asm/cpufeatures.h
>> + if (file == 1)
>> + FS = "[ \t()*+]+";
>> +
>> + # .config
>> + if (file == 2)
>> + FS = "=";
>> +}
>> +
>> +# Create a dictionary of sorts, containing all defined feature bits
>> +file == 1 && $1 ~ /^#define$/ && $2 ~ /^X86_FEATURE_/ {
>> + nfeat = $3 * $4 + $5;
>> + feat = $2;
>> + sub(/^X86_FEATURE_/, "", feat);
>> + feats[nfeat] = feat;
>> +}
>> +file == 1 && $1 ~ /^#define$/ && $2 == "NCAPINTS" {
>> + ncapints = int($3);
>> +}
>> +
>> +# Create a dictionary featstat[REQUIRED|DISABLED, FEATURE_NAME] = on | off
>> +file == 2 && $1 ~ /^CONFIG_X86_(REQUIRED|DISABLED)_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++) {
>> + feat = feats[i*32 + j];
>> + if (featstat[s, feat]) {
>> + nfstr = fstr " " feat;
>> + if (length(nfstr) > 72) {
>> + printf " * %s\n", fstr;
>> + nfstr = " " feat;
>> + }
>> + fstr = nfstr;
>> + mask += (2 ^ j);
>> + }
>> + }
>> + masks[i] = mask;
>> + }
>> + printf " * %s\n */\n", fstr;
>> +
>> + for (i = 0; i < ncapints; i++)
>> + printf "#define %s_MASK%d\t0x%08xU\n", s, i, masks[i];
>> +
>> + printf "#define %s_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != %d)\n\n", s, ncapints;
>> + }
>> +
>> + printf "#endif /* _ASM_X86_FEATUREMASKS_H */\n";
>> +}
>
>
>
>Building kselftests is regressing with this commit on next-20250303.
>
># make headers
> HOSTCC scripts/basic/fixdep
> HOSTCC scripts/unifdef
> WRAP arch/x86/include/generated/uapi/asm/bpf_perf_event.h
> WRAP arch/x86/include/generated/uapi/asm/errno.h
> WRAP arch/x86/include/generated/uapi/asm/fcntl.h
> WRAP arch/x86/include/generated/uapi/asm/ioctl.h
> WRAP arch/x86/include/generated/uapi/asm/ioctls.h
> WRAP arch/x86/include/generated/uapi/asm/ipcbuf.h
> WRAP arch/x86/include/generated/uapi/asm/param.h
> WRAP arch/x86/include/generated/uapi/asm/poll.h
> WRAP arch/x86/include/generated/uapi/asm/resource.h
> WRAP arch/x86/include/generated/uapi/asm/socket.h
> WRAP arch/x86/include/generated/uapi/asm/sockios.h
> WRAP arch/x86/include/generated/uapi/asm/termbits.h
> WRAP arch/x86/include/generated/uapi/asm/termios.h
> WRAP arch/x86/include/generated/uapi/asm/types.h
>make[1]: *** No rule to make target '.config', needed by 'arch/x86/include/generated/asm/featuremasks.h'. Stop.
>make: *** [Makefile:251: __sub-make] Error 2
>
>The same used to work fine until next-20250228.
>
>Recreation steps:
>1. Clone next-20250303
>2. make distclean
>3. make headers
>
>Srikanth Aithal <sraithal@xxxxxxx>

"make headers" on an unconfigured tree should presumably only produce the uapi headers, not kernel-internal ones, one could surmise?

Next message: Ulf Hansson: "Re: [PATCH v1 0/5] PM: sleep: Improvements of async suspend and resume of devices"
Previous message: Andy Shevchenko: "Re: [PATCH v5 02/10] property: Add functions to count named child nodes"
In reply to: Aithal, Srikanth: "Re: [PATCH v6 3/5] x86/cpufeatures: Generate a feature mask header based on build config"
Next in thread: Borislav Petkov: "Re: [PATCH v6 3/5] x86/cpufeatures: Generate a feature mask header based on build config"
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