When implementing a system call, how do you expose the system call number to userland?

I'm fiddling with system calls. I've added two new ones and verified they work using calls to syscall.

I would like the syscall numbers to be in a header so that userspace does not have to know the syscall number explicitly.

In arch/x86/syscalls/syscall_64.tbl I have:

317     64      krun_read_msrs                  sys_krun_read_msrs
318     64      krun_reset_msrs                 sys_krun_reset_msrs

And some grepping suggests that kbuild has auto-generated the macros for the new syscalls:

$ ag __NR_krun *
arch/x86/include/generated/uapi/asm/unistd_64.h
321:#define __NR_krun_read_msrs 317
322:#define __NR_krun_reset_msrs 318

The filename suggests that I don't need to add the entries manually, but this is contrary to what the Linux Kernel docs have to say:

Some architectures (e.g. x86) have their own architecture-specific syscall tables, but several other architectures share a generic syscall table. Add your new system call to the generic list by adding an entry to the list in include/uapi/asm-generic/unistd.h:

#define __NR_xyzzy 292
__SYSCALL(__NR_xyzzy, sys_xyzzy)

Well, my syscalls are x86_64 specific, since they read and write MSRs found only in Intel chips. So after this, I went digging to see if I could find the arch-specific header for my amd64 system.

You would expect it to be under arch/x86_64 but there are no includes at all in there. So I assume x86_64 inherits from x86. That being the case, the arch-specific header should be:

arch/x86/include/uapi/asm/unistd.h

If you open that up, it's just a little wrapper to dispatch based on arch:

# ifdef __i386__                                                                
#  include <asm/unistd_32.h>                                                    
# elif defined(__ILP32__)                                                       
#  include <asm/unistd_x32.h>                                                   
# else                                                                          
#  include <asm/unistd_64.h>                                                    
# endif

So that's presumably designed to pick up /usr/include/x86_64-linux-gnu/asm/unistd.h, but this does not yet include my new syscall numbers.

I'd expect the headers_install target to install the new headers (perhaps), but alas it does not.

I'm confused. Should I add my new syscalls to a file manually or not? If so which file? If not, how do I expose the auto-generated __NR_* macros to userspace in a standard location?

Thanks