Re: [PATCH 2/3] vmsplice: make vmsplice a trivial wrapper for preadv2/pwritev2

[Linus Torvalds]

On Fri, 5 Jun 2026 at 02:33, Florian Weimer <fweimer@xxxxxxxxxx> wrote:
>
> * Linus Torvalds:
>
> > x86 really doesn't *care*. If the caller zero-extends or leaves high
> > bits set randomly, according to the x86 ABI that's perfectly fine: the
> > callee will only care about the low 32 bits. So the high bits are
> > simply not relevant for the ABI.
>
> Please note that Clang does not implement the x86-64 ABI and requires
> zero extension.  We see increasing problems from that, now that we have
> more C code calling Rust code.

Uhhuh. But that is only specific to 'bool', right?

If it were to have the same issue that powerpc(*) had - that 'unsigned
int' has to be passed to functions with well-defined high bits - that
would be bad.

And I'm pretty sure that clang doesn't do that.

Anyway, for the kernel, this shouldn't be an issue simply because we
typically avoid 'bool' in arguments or structures that are exposed to
outside.

(I say 'typically' because I'm sure it happens in some broken UAPI
thing anyway).

                  Linus

(*) I may mis-remember. Maybe it was s390, not powerpc. The s390
compat layer independently had a similar issue wrt pointers, where bit
31 had to be cleared. s390 dropped the 31-bit code entirely fairly
recently, but it caused some "interesting" code in the already
disgusting syscall argument handling wrapper macros.