Re: [patch 16/18] x86/entry: Get rid of the sys_ni_syscall() indirection

On 7/8/2026 3:07 AM, Thomas Gleixner wrote:
> Invoking sys_ni_syscall() from a code path, which already knows that the
> syscall number is invalid just to assign -ENOSYS to regs->ax is a pointless
> exercise. It's even redundant as the low level entry code already has set
> regs->ax to -ENOSYS on entry.

Makes sense, the all reltaed entry has already initialized
regs->ax to -ENOSYS.

This makes the code very concise.

LGTM
Reviewed-by: Jinjie Ruan <[email protected]>

> 
> Remove the extra conditionals and the function calls.
> 
> Signed-off-by: Thomas Gleixner <[email protected]>
> ---
>  arch/x86/entry/syscall_32.c |    2 --
>  arch/x86/entry/syscall_64.c |   10 +++-------
>  2 files changed, 3 insertions(+), 9 deletions(-)
> 
> --- a/arch/x86/entry/syscall_32.c
> +++ b/arch/x86/entry/syscall_32.c
> @@ -81,8 +81,6 @@ static __always_inline void do_syscall_3
>  	if (likely(unr < IA32_NR_syscalls)) {
>  		unr = array_index_nospec(unr, IA32_NR_syscalls);
>  		regs->ax = ia32_sys_call(regs, unr);
> -	} else if (nr != -1) {
> -		regs->ax = __ia32_sys_ni_syscall(regs);
>  	}
>  }
>  
> --- a/arch/x86/entry/syscall_64.c
> +++ b/arch/x86/entry/syscall_64.c
> @@ -68,7 +68,7 @@ static __always_inline bool do_syscall_x
>  	return false;
>  }
>  
> -static __always_inline bool do_syscall_x32(struct pt_regs *regs, int nr)
> +static __always_inline void do_syscall_x32(struct pt_regs *regs, int nr)
>  {
>  	/*
>  	 * Adjust the starting offset of the table, and convert numbers
> @@ -80,9 +80,7 @@ static __always_inline bool do_syscall_x
>  	if (IS_ENABLED(CONFIG_X86_X32_ABI) && likely(xnr < X32_NR_syscalls)) {
>  		xnr = array_index_nospec(xnr, X32_NR_syscalls);
>  		regs->ax = x32_sys_call(regs, xnr);
> -		return true;
>  	}
> -	return false;
>  }
>  
>  /* Returns true to return using SYSRET, or false to use IRET */
> @@ -92,10 +90,8 @@ static __always_inline bool do_syscall_x
>  
>  	instrumentation_begin();
>  
> -	if (!do_syscall_x64(regs, nr) && !do_syscall_x32(regs, nr) && nr != -1) {
> -		/* Invalid system call, but still a system call. */
> -		regs->ax = __x64_sys_ni_syscall(regs);
> -	}
> +	if (!do_syscall_x64(regs, nr))
> +		do_syscall_x32(regs, nr);
>  
>  	instrumentation_end();
>  	syscall_exit_to_user_mode(regs);
>