linux-kernel - Re: [PATCH v3 44/64] x86/jump_label: Define ELF section entry size for jump labels

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Message-ID: <20250630073522.GF1613200@noisy.programming.kicks-ass.net>
Date: Mon, 30 Jun 2025 09:35:22 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Petr Mladek <pmladek@...e.com>, Miroslav Benes <mbenes@...e.cz>,
	Joe Lawrence <joe.lawrence@...hat.com>,
	live-patching@...r.kernel.org, Song Liu <song@...nel.org>,
	laokz <laokz@...mail.com>, Jiri Kosina <jikos@...nel.org>,
	Marcos Paulo de Souza <mpdesouza@...e.com>,
	Weinan Liu <wnliu@...gle.com>,
	Fazla Mehrab <a.mehrab@...edance.com>,
	Chen Zhongjin <chenzhongjin@...wei.com>,
	Puranjay Mohan <puranjay@...nel.org>,
	Dylan Hatch <dylanbhatch@...gle.com>
Subject: Re: [PATCH v3 44/64] x86/jump_label: Define ELF section entry size
 for jump labels

On Fri, Jun 27, 2025 at 09:55:30AM -0700, Josh Poimboeuf wrote:
> On Fri, Jun 27, 2025 at 12:48:18PM +0200, Peter Zijlstra wrote:
> > > +#define JUMP_TABLE_ENTRY(key, label)				\
> > > +	".pushsection __jump_table,  \"aM\", @progbits, "	\
> > > +	__stringify(JUMP_ENTRY_SIZE) "\n\t"			\
> > 
> > Argh, can you please not do this line-break. Yes it'll be long, but this
> > is most confusing.
> 
> Yeah, I'll go indent that like the extable one.
> 
> > > @@ -29,6 +30,9 @@ int main(void)
> > >  #else
> > >  	DEFINE(LRU_GEN_WIDTH, 0);
> > >  	DEFINE(__LRU_REFS_WIDTH, 0);
> > > +#endif
> > > +#if defined(CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE) && defined(CONFIG_JUMP_LABEL)
> > 
> > How is HAVE_ARCH_JUMP_LABEL_RELATIVE relevant here?
> 
> #ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
> 
> struct jump_entry {
> 	s32 code;
> 	s32 target;
> 	long key;	// key may be far away from the core kernel under KASLR
> };

Well,... that's odd. I was sure there was a
!HAVE_ARCH_JUMP_LABEL_RELATIVE version somewhere... Oh well.