linux-kernel - Re: [PATCH v5 1/3] x86/syscall: Mark exit[_group] syscall handlers _

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Date: Tue, 25 Jun 2024 22:21:17 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Nikolay Borisov <nik.borisov@...e.com>
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>,
	KP Singh <kpsingh@...nel.org>, Waiman Long <longman@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH v5 1/3] x86/syscall: Mark exit[_group] syscall handlers
 __noreturn

On Mon, May 27, 2024 at 02:15:57PM +0300, Nikolay Borisov wrote:
> 
> 
> On 7.05.24 г. 8:30 ч., 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 those 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
> > Tested-by: Paul E. McKenney <paulmck@...nel.org>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> > ---
> >   arch/x86/entry/syscall_32.c            | 10 ++++++----
> >   arch/x86/entry/syscall_64.c            |  9 ++++++---
> >   arch/x86/entry/syscall_x32.c           |  7 +++++--
> >   arch/x86/entry/syscalls/syscall_32.tbl |  6 +++---
> >   arch/x86/entry/syscalls/syscall_64.tbl |  6 +++---
> >   arch/x86/um/sys_call_table_32.c        | 10 ++++++----
> >   arch/x86/um/sys_call_table_64.c        | 11 +++++++----
> >   scripts/syscalltbl.sh                  | 18 ++++++++++++++++--
> >   tools/objtool/noreturns.h              |  4 ++++
> >   9 files changed, 56 insertions(+), 25 deletions(-)
> > 
> > diff --git a/arch/x86/entry/syscall_32.c b/arch/x86/entry/syscall_32.c
> > index c2235bae17ef..8cc9950d7104 100644
> > --- a/arch/x86/entry/syscall_32.c
> > +++ b/arch/x86/entry/syscall_32.c
> > @@ -14,9 +14,12 @@
> >   #endif
> >   #define __SYSCALL(nr, sym) extern long __ia32_##sym(const struct pt_regs *);
> > -
> > +#define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __ia32_##sym(const struct pt_regs *);
> >   #include <asm/syscalls_32.h>
> > -#undef __SYSCALL
> > +#undef  __SYSCALL
> > +
> > +#undef  __SYSCALL_NORETURN
> > +#define __SYSCALL_NORETURN __SYSCALL
> >   /*
> >    * The sys_call_table[] is no longer used for system calls, but
> > @@ -28,11 +31,10 @@
> >   const sys_call_ptr_t sys_call_table[] = {
> >   #include <asm/syscalls_32.h>
> >   };
> > -#undef __SYSCALL
> > +#undef  __SYSCALL
> 
> nit: Am I blind or all the __SYSCALL lines have an extra whitespace?
> 
> <snip>

That was a small readability tweak to make '__SYSCALL' vertically aligned:

#define __SYSCALL(nr, sym) extern long __ia32_##sym(const struct pt_regs *);
#define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __ia32_##sym(const struct pt_regs *);
#include <asm/syscalls_32.h>
#undef  __SYSCALL

-- 
Josh