linux-kernel - Re: [PATCH RFC 4/5] x86/alternative: Improve code generation readability

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Message-ID: <focwffxfbjx3gwobutrfkqvagfw2dt6zvyesejta4sosuporkh@xnhk4uofwadj>
Date: Wed, 16 Apr 2025 16:30:02 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>, x86@...nel.org, 
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH RFC 4/5] x86/alternative: Improve code generation
 readability

On Wed, Apr 09, 2025 at 11:02:29AM -0700, Linus Torvalds wrote:
> On Wed, 9 Apr 2025 at 10:41, Josh Poimboeuf <jpoimboe@...nel.org> wrote:
> >
> > I actually think the compactness of putting the entry on a single line
> > is really nice.
> 
> Yeah, I think the noise with size calculations in particular is stuff
> that I never look at, and making it one long line is better than
> multiple lines, I think.

We could just give up on trying to making the code itself readable, and
instead put the code+features in comments, e.g.:

# <ALTERNATIVE>
#
# ORIG:	rep movsb
# NEW:	call rep_movs_alternative	# ALT_NOT(X86_FEATURE_FSRM)
#
771: rep movsb; 772: .skip -(((775f-774f)-(772b-771b)) > 0) * ((775f-774f)-(772b-771b)),0x90; 773: .pushsection .altinstructions,"a"; .long 771b - .; .long 774f - .; .4byte (((1 << 0) << 16) | ((18*32+ 4))); .byte 773b-771b; .byte 775f-774f; .popsection; .pushsection .altinstr_replacement, "ax"; 774: call rep_movs_alternative; 775: .popsection
# </ALTERNATIVE>

-- 
Josh