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Message-ID: <71d3a15e-6998-42d6-a56a-5664ce50a5cd@oracle.com>
Date: Tue, 25 Nov 2025 15:43:10 +0100
From: Alexandre Chartre <alexandre.chartre@...cle.com>
To: David Laight <david.laight.linux@...il.com>
Cc: alexandre.chartre@...cle.com, 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 11/25/25 14:29, David Laight wrote:
> 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.
Sure, I can do that.
>
>> +
>> + 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 "\","
I presume you mean: print "\t[" $3 "] = \"" $2 "\","
But this doesn't always work because the value we need can contain spaces
and then it will be split into several fields.
For example, this works with:
#define X86_FEATURE_RRSBA_CTRL (11*32+11) /* RET prediction control */
But not with:
#define X86_FEATURE_APIC ( 0*32+ 9) /* "apic" Onboard APIC */
alex.
>
>> +}
>> +
>> +/^#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 */
>
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