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: <20251125183425.28880170@pumpkin>
Date: Tue, 25 Nov 2025 18:34:25 +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 Tue, 25 Nov 2025 15:43:10 +0100
Alexandre Chartre <alexandre.chartre@...cle.com> wrote:

> 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 "\","

No $2 and $2, so it generates:
	[X86_FEATURE_RRSBA_CTRL] = "X86_FEATURE_RRSBA_CTRL",

All the #defines are defined - so you might as well use them.
I suggested this sed command that has the same effect:
	sed -n -E '/^#define (X86_(FEATURE|BUG)_([^	 ]*)).*/s//	[\1] = "\1",/p'
which can be put directly into the makefile.

It isn't as though the pattern match for lines has to be very selective.
It just needs to be 'good enough' for the current file.

	David

> 
> 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.
>