linux-kernel - Re: [PATCH v6 26/30 (mawk fix)] objtool: Add function to get the name of a CPU feature

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Message-ID: <20251125132902.0cace2c8@pumpkin>
Date: Tue, 25 Nov 2025 13:29:02 +0000
From: David Laight <david.laight.linux@...il.com>
To: Alexandre Chartre <alexandre.chartre@...cle.com>
Cc: linux-kernel@...r.kernel.org, mingo@...nel.org, jpoimboe@...nel.org,
 peterz@...radead.org
Subject: Re: [PATCH v6 26/30 (mawk fix)] objtool: Add function to get the
 name of a CPU feature

On Mon, 24 Nov 2025 17:48:55 +0100
Alexandre Chartre <alexandre.chartre@...cle.com> wrote:

> Add a function to get the name of a CPU feature. The function is
> architecture dependent and currently only implemented for x86. The
> feature names are automatically generated from the cpufeatures.h
> include file.
> 
> Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>
> Link: https://patch.msgid.link/20251121095340.464045-27-alexandre.chartre@oracle.com
> ---
>  .../x86/tools/gen-cpu-feature-names-x86.awk   | 34 +++++++++++++++++++
>  tools/objtool/.gitignore                      |  1 +
>  tools/objtool/Makefile                        |  1 +
>  tools/objtool/arch/loongarch/special.c        |  5 +++
>  tools/objtool/arch/powerpc/special.c          |  5 +++
>  tools/objtool/arch/x86/Build                  | 10 ++++++
>  tools/objtool/arch/x86/special.c              | 10 ++++++
>  tools/objtool/include/objtool/special.h       |  2 ++
>  8 files changed, 68 insertions(+)
>  create mode 100644 tools/arch/x86/tools/gen-cpu-feature-names-x86.awk
> 
> diff --git a/tools/arch/x86/tools/gen-cpu-feature-names-x86.awk b/tools/arch/x86/tools/gen-cpu-feature-names-x86.awk
> new file mode 100644
> index 0000000000000..cc4c7a3e6c2e2
> --- /dev/null
> +++ b/tools/arch/x86/tools/gen-cpu-feature-names-x86.awk
> @@ -0,0 +1,34 @@
> +#!/bin/awk -f
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Copyright (c) 2025, Oracle and/or its affiliates.
> +#
> +# Usage: awk -f gen-cpu-feature-names-x86.awk cpufeatures.h > cpu-feature-names.c
> +#
> +
> +BEGIN {
> +	print "/* cpu feature name array generated from cpufeatures.h */"
> +	print "/* Do not change this code. */"
> +	print
> +	print "static const char *cpu_feature_names[(NCAPINTS+NBUGINTS)*32] = {"

Since this code is #include'd into a .c file the line above (and the final })
can be in that source file.
You only need to generate the initialisers here.

> +
> +	value_expr = "\\([0-9*+ ]+\\)"
> +}
> +
> +/^#define X86_FEATURE_/ {
> +	if (match($0, value_expr)) {
> +		value = substr($0, RSTART + 1, RLENGTH - 2)
> +		print "\t[" value "] = \"" $2 "\","
> +	}

Can't you just do:
	print "\t[" $2 "] = \"" $2 "\","

    David

> +}
> +
> +/^#define X86_BUG_/ {
> +	if (match($0, value_expr)) {
> +		value = substr($0, RSTART + 1, RLENGTH - 2)
> +		print "\t[NCAPINTS*32+(" value ")] = \"" $2 "\","
> +	}
> +}
> +
> +END {
> +	print "};"
> +}
> diff --git a/tools/objtool/.gitignore b/tools/objtool/.gitignore
> index 759303657bd7c..73d883128511f 100644
> --- a/tools/objtool/.gitignore
> +++ b/tools/objtool/.gitignore
> @@ -1,4 +1,5 @@
>  # SPDX-License-Identifier: GPL-2.0-only
> +arch/x86/lib/cpu-feature-names.c
>  arch/x86/lib/inat-tables.c
>  /objtool
>  feature
> diff --git a/tools/objtool/Makefile b/tools/objtool/Makefile
> index df793ca6fc1a1..66397d755fe4b 100644
> --- a/tools/objtool/Makefile
> +++ b/tools/objtool/Makefile
> @@ -125,6 +125,7 @@ $(LIBSUBCMD)-clean:
>  clean: $(LIBSUBCMD)-clean
>  	$(call QUIET_CLEAN, objtool) $(RM) $(OBJTOOL)
>  	$(Q)find $(OUTPUT) -name '*.o' -delete -o -name '\.*.cmd' -delete -o -name '\.*.d' -delete
> +	$(Q)$(RM) $(OUTPUT)arch/x86/lib/cpu-feature-names.c $(OUTPUT)fixdep
>  	$(Q)$(RM) $(OUTPUT)arch/x86/lib/inat-tables.c $(OUTPUT)fixdep
>  	$(Q)$(RM) -- $(OUTPUT)FEATURE-DUMP.objtool
>  	$(Q)$(RM) -r -- $(OUTPUT)feature
> diff --git a/tools/objtool/arch/loongarch/special.c b/tools/objtool/arch/loongarch/special.c
> index a80b75f7b061f..aba774109437f 100644
> --- a/tools/objtool/arch/loongarch/special.c
> +++ b/tools/objtool/arch/loongarch/special.c
> @@ -194,3 +194,8 @@ struct reloc *arch_find_switch_table(struct objtool_file *file,
>  
>  	return rodata_reloc;
>  }
> +
> +const char *arch_cpu_feature_name(int feature_number)
> +{
> +	return NULL;
> +}
> diff --git a/tools/objtool/arch/powerpc/special.c b/tools/objtool/arch/powerpc/special.c
> index 51610689abf72..8f9bf61ca0899 100644
> --- a/tools/objtool/arch/powerpc/special.c
> +++ b/tools/objtool/arch/powerpc/special.c
> @@ -18,3 +18,8 @@ struct reloc *arch_find_switch_table(struct objtool_file *file,
>  {
>  	exit(-1);
>  }
> +
> +const char *arch_cpu_feature_name(int feature_number)
> +{
> +	return NULL;
> +}
> diff --git a/tools/objtool/arch/x86/Build b/tools/objtool/arch/x86/Build
> index 3dedb2fd8f3a0..b95448ee01ee4 100644
> --- a/tools/objtool/arch/x86/Build
> +++ b/tools/objtool/arch/x86/Build
> @@ -12,3 +12,13 @@ $(OUTPUT)arch/x86/lib/inat-tables.c: $(inat_tables_script) $(inat_tables_maps)
>  $(OUTPUT)arch/x86/decode.o: $(OUTPUT)arch/x86/lib/inat-tables.c
>  
>  CFLAGS_decode.o += -I$(OUTPUT)arch/x86/lib
> +
> +cpu_features = ../arch/x86/include/asm/cpufeatures.h
> +cpu_features_script = ../arch/x86/tools/gen-cpu-feature-names-x86.awk
> +
> +$(OUTPUT)arch/x86/lib/cpu-feature-names.c: $(cpu_features_script) $(cpu_features)
> +	$(Q)$(call echo-cmd,gen)$(AWK) -f $(cpu_features_script) $(cpu_features) > $@
> +
> +$(OUTPUT)arch/x86/special.o: $(OUTPUT)arch/x86/lib/cpu-feature-names.c
> +
> +CFLAGS_special.o := -I$(OUTPUT)arch/x86/lib
> diff --git a/tools/objtool/arch/x86/special.c b/tools/objtool/arch/x86/special.c
> index 09300761f1085..e817a3fff4491 100644
> --- a/tools/objtool/arch/x86/special.c
> +++ b/tools/objtool/arch/x86/special.c
> @@ -4,6 +4,10 @@
>  #include <objtool/special.h>
>  #include <objtool/builtin.h>
>  #include <objtool/warn.h>
> +#include <asm/cpufeatures.h>
> +
> +/* cpu feature name array generated from cpufeatures.h */
> +#include "cpu-feature-names.c"
>  
>  void arch_handle_alternative(struct special_alt *alt)
>  {
> @@ -134,3 +138,9 @@ struct reloc *arch_find_switch_table(struct objtool_file *file,
>  	*table_size = 0;
>  	return rodata_reloc;
>  }
> +
> +const char *arch_cpu_feature_name(int feature_number)
> +{
> +	return (feature_number < ARRAY_SIZE(cpu_feature_names)) ?
> +		cpu_feature_names[feature_number] : NULL;
> +}
> diff --git a/tools/objtool/include/objtool/special.h b/tools/objtool/include/objtool/special.h
> index b22410745e4a1..121c3761899c1 100644
> --- a/tools/objtool/include/objtool/special.h
> +++ b/tools/objtool/include/objtool/special.h
> @@ -38,4 +38,6 @@ bool arch_support_alt_relocation(struct special_alt *special_alt,
>  struct reloc *arch_find_switch_table(struct objtool_file *file,
>  				     struct instruction *insn,
>  				     unsigned long *table_size);
> +const char *arch_cpu_feature_name(int feature_number);
> +
>  #endif /* _SPECIAL_H */