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

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Date: Mon, 27 May 2024 14:15:57 +0300
From: Nikolay Borisov <nik.borisov@...e.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org
Cc: 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>, "Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: [PATCH v5 1/3] x86/syscall: Mark exit[_group] syscall handlers
 __noreturn

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>