On Sun, Nov 27, 2022, at 21:18, Jason A. Donenfeld wrote:

quoted

config GENERIC_VDSO_RANDOM_WHATEVER
       bool
       select VGETRANDOM_ALLOC

This gives a clear Kconfig dependency instead of the random
ADVISE_SYSCALLS select.

That's much better indeed. I was trying to straddle the two conventions
of `#define __ARCH_...` for syscalls and a Kconfig for vDSO functions,
but doing it all together as you've suggested is nicer.

I'll try to figure this out, though so far futzing around suggests there
might have to be both, because of unistd.h being a userspace header.
That is, include/uapi/asm-generic/unistd.h typically needs a `#if
__ARCH_WANT..., #define ...` in it. I'll give it a spin and you'll see
for v8. At the very least it should get rid of the more awkward
`select ADVISE_SYSCALLS if X86_64` part, and will better separate the
arch code from non-arch code.

I think you should not need an __ARCH_WANT_SYS_* symbol for this,
the only place we actually need them for is the asm-generic/unistd.h
header which is still used on a couple of architectures (I have
an experimental series for replacing it with a generic syscall.tbl
file, but it's not ready for 6.2). In most cases, the __ARCH_WANT_SYS_*
symbols are only used for syscalls that are part of the table for
old architectures but get skipped on newer targets that always had
a replacement syscalls (e.g. getrlimit getting replaced by prlimit64)

I think we should just reserve the syscall number for all architectures
right away and #define the __NR_* macro. libc will generally need
a runtime check anyway, and defining it now avoids the problem of
the tables getting out of sync.

The Kconfig symbol is fine in this case.

      Arnd