linux-kernel - Re: [PATCH v6 1/3] x86/syscall: Mark exit[_group] syscall handlers _

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Message-ID: <20240627072634.GAZn0UKqtwqwQhWr4q@fat_crate.local>
Date: Thu, 27 Jun 2024 09:26:34 +0200
From: Borislav Petkov <bp@...en8.de>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexandre Chartre <alexandre.chartre@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	KP Singh <kpsingh@...nel.org>, Waiman Long <longman@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH v6 1/3] x86/syscall: Mark exit[_group] syscall handlers
 __noreturn

On Tue, Jun 25, 2024 at 11:02:00PM -0700, Josh Poimboeuf wrote:
> The direct-call syscall dispatch function doesn't know that the exit()
> and exit_group() syscall handlers don't return, so the call sites aren't
> optimized accordingly.
> 
> Fix that by marking the exit syscall declarations __noreturn.
> 
> Fixes the following warnings:
> 
>   vmlinux.o: warning: objtool: x64_sys_call+0x2804: __x64_sys_exit() is missing a __noreturn annotation
>   vmlinux.o: warning: objtool: ia32_sys_call+0x29b6: __ia32_sys_exit_group() is missing a __noreturn annotation
> 
> Fixes: 7390db8aea0d ("x86/bhi: Add support for clearing branch history at syscall entry")
> Reported-by: "Paul E. McKenney" <paulmck@...nel.org>
> Closes: https://lkml.kernel.org/lkml/6dba9b32-db2c-4e6d-9500-7a08852f17a3@paulmck-laptop

This here talks about

1e3ad78334a6 ("x86/syscall: Don't force use of indirect calls for system calls")

being the culprit.

But Fixes points to something unrelated...?

In any case, I won't send this to Linus now as urgent material unless someone
presents a reasonable argument for it...

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette