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

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Message-ID: <CAJzB8QF_+51+rrJmq3iXkaAbmbbyKYVf0m_LpQCRSLS_FgHUMQ@mail.gmail.com>
Date: Sun, 21 Apr 2024 13:40:43 -0700
From: Paul McKenney <paulmckrcu@...il.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: "Paul E. McKenney" <paulmck@...nel.org>, 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

They apply fine as is, so I have started tests with that pair of patches.

                                              Thanx, Paul

On Sat, Apr 20, 2024 at 10:25 PM Josh Poimboeuf <jpoimboe@...nel.org> wrote:
>
> 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