linux-kernel - Re: [GIT PULL] objtool fixes

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Message-ID: <CAHk-=wgqa0B9OV+EAQ34-VOUAeVB2o2bXnZXQDG7u+Z=4Cmw8w@mail.gmail.com>
Date: Wed, 2 Apr 2025 10:58:15 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <a.p.zijlstra@...llo.nl>, 
	Josh Poimboeuf <jpoimboe@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, 
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] objtool fixes

On Tue, 1 Apr 2025 at 12:57, Ingo Molnar <mingo@...nel.org> wrote:
>
>  - Fix a number of objtool warnings in various drivers, core kernel
>    code and architecture code. About half of them are potential
>    problems related to out-of-bounds accesses or potential undefined
>    behavior, the other half are additional objtool annotations.

So I've pulled this, but I really dislike some of it.

That

> Josh Poimboeuf (35):
>       objtool: Fix X86_FEATURE_SMAP alternative handling

makes a bad thing even worse.

Apparently nobody else ever looks at generated code, but dammit, the
clac/stac code generation has turned the ugly up to 11.

Yes, the altinstruction replacement thing was already making the
generated asm hard to read, but now it's *also* adding this garbage to
it:

        911:
        .pushsection .discard.annotate_insn,"M",@progbits,8
        .long 911b - .
        .long 6
        .popsection

which is just pure unadulterated pointless noise.

That "annotation #6" is WORTHLESS.

Dammit, objtool could have figured that annotation out ON ITS OWN
without generating shit in our code. It's not like it doesn't already
look at alternatives, and it's not like it couldn't just have seen
"oh, look, it's a nop instruction with a clac/stac instruction as an
alternative".

So why does it add that pointless garbage that makes already nasty
code even nastier?

Please fix this.

            Linus