linux-kernel - Re: [PATCH 17/29] x86/ibt: Annotate text references

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Date:   Fri, 18 Feb 2022 21:22:16 -0800
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com
Subject: Re: [PATCH 17/29] x86/ibt: Annotate text references

On Fri, Feb 18, 2022 at 05:49:19PM +0100, Peter Zijlstra wrote:
> Annotate away some of the generic code references. This is things
> where we take the address of a symbol for exception handling or return
> addresses (eg. context switch).
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

The vast majority of these annotations can go away if objtool only
requires ENDBR for referenced *STT_FUNC* symbols.

Anything still needing ANNOTATE_NOENDBR after that, might arguably not
belong as STT_FUNC anyway and it might make sense to convert it to
non-function code (e.g. SYM_CODE{START,END}.

> @@ -564,12 +565,16 @@ SYM_CODE_END(\asmsym)
>  	.align 16
>  	.globl __irqentry_text_start
>  __irqentry_text_start:
> +	ANNOTATE_NOENDBR // unwinders
> +	ud2;
>  
>  #include <asm/idtentry.h>
>  
>  	.align 16
>  	.globl __irqentry_text_end
>  __irqentry_text_end:
> +	ANNOTATE_NOENDBR
> +	ud2;

Why ud2?  If no ud2 then the annotation shouldn't be needed since the
first idt entry has ENDBR.

-- 
Josh