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

["H. Peter Anvin" <hpa@zytor.com>]

On March 3, 2025 3:38:05 AM PST, "Aithal, Srikanth" <sraithal@amd.com> wrote:
>On 2/28/2025 1:53 PM, Xin Li (Intel) wrote:
>> From: "H. Peter Anvin (Intel)" <hpa@zytor.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@zytor.com>
>> Signed-off-by: Xin Li (Intel) <xin@zytor.com>
>> Reviewed-by: Nikolay Borisov <nik.borisov@suse.com>
>> ---
>> 
>> 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@amd.com>

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