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

[Alexandre Chartre <alexandre.chartre@oracle.com>]

On 11/25/25 14:29, David Laight wrote:
> On Mon, 24 Nov 2025 17:48:55 +0100
> Alexandre Chartre <alexandre.chartre@oracle.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@oracle.com>
>> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>> Acked-by: Josh Poimboeuf <jpoimboe@kernel.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 */
>