linux-kernel - Re: [PATCH v4 3/5] x86/syscall: Mark exit[_group] syscall handlers _

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Date: Sat, 20 Apr 2024 22:25:40 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: "Paul E. McKenney" <paulmck@...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>,
	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v4 3/5] x86/syscall: Mark exit[_group] syscall handlers
 __noreturn

On Sat, Apr 20, 2024 at 06:58:58AM -0700, Paul E. McKenney wrote:
> On Fri, Apr 19, 2024 at 02:09:49PM -0700, Josh Poimboeuf wrote:
> > The direct-call syscall dispatch functions don't know that the exit()
> > and exit_group() syscall handlers don't return.  As a result the call
> > sites aren't optimized accordingly.
> > 
> > Fix that by marking those exit syscall declarations as __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
> > Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> 
> Looks good, but it does not apply on top of current -next and I don't
> trust myself to hand-apply it (something about having just got off of
> a flight across the big pond).
> 
> Could you please let me know what else do I need to pull in to be able
> to cleanly apply this one?

This patch has a dependency on an earlier patch in the set:

  https://lkml.kernel.org/lkml/982d05a2f669140f26500bee643011896d661094.1713559768.git.jpoimboe@kernel.org

Though I think it's not a hard dependency and I could reverse the order
of the patches if needed.

-- 
Josh