Re: [patch 06/12] rseq: Implement sys_rseq_slice_yield()

[K Prateek Nayak <kprateek.nayak@amd.com>]

Hello Thomas,

On 9/9/2025 4:30 AM, Thomas Gleixner wrote:
> --- a/kernel/rseq.c
> +++ b/kernel/rseq.c
> @@ -542,6 +542,15 @@ int rseq_slice_extension_prctl(unsigned
>  	return -EFAULT;
>  }
>  
> +SYSCALL_DEFINE0(rseq_slice_yield)
> +{
> +	if (need_resched()) {
> +		schedule();
> +		return 1;
> +	}
> +	return 0;
> +}
> +
>  static int __init rseq_slice_cmdline(char *str)
>  {
>  	bool on;
> --- a/kernel/sys_ni.c
> +++ b/kernel/sys_ni.c
> @@ -390,5 +390,6 @@ COND_SYSCALL(setuid16);
>  
>  /* restartable sequence */
>  COND_SYSCALL(rseq);
> +COND_SYSCALL(rseq_sched_yield);

I'm not sure if it is my toolchain but when I try to build a version
with CONFIG_RSEQ_SLICE_EXTENSION disabled, I see:

    ld: vmlinux.o: in function `x64_sys_call':
    arch/x86/include/generated/asm/syscalls_64.h:471: undefined reference to `__x64_sys_rseq_slice_yield'
    ld: vmlinux.o: in function `ia32_sys_call':
    arch/x86/include/generated/asm/syscalls_32.h:471: undefined reference to `__ia32_sys_rseq_slice_yield'
    ld: vmlinux.o:(.rodata+0x12d0): undefined reference to `__x64_sys_rseq_slice_yield'

I would have assumed the COND_SYSCALL() above would have stubbed this
but that doesn't seem to be the case. Am I missing something?
P.S. I'm running with:

    gcc version 11.4.0 (Ubuntu 11.4.0-1ubuntu1~22.04.2)
    GNU ld (GNU Binutils for Ubuntu) 2.38

-- 
Thanks and Regards,
Prateek