[RFC/PATCH] powerpc: Cleanup 32/64 bit syscall int sign ext.

[Josh Boyer]

On Thu, Sep 25, 2008 at 05:01:36PM +1000, Benjamin Herrenschmidt wrote:
>I noticed that our ABI says callers are responsible for sign extending.
>That means that all int, long or similarly signed arguments to syscalls
>must be explicitly sign-extended.
>
>We already have wrappers to do that for -some- syscalls in arch code.
>Those are in C and pretty ugly, copy/pasting a bunch of identically
>useless comments all over, and are missing a lot of potential
>candidates.
>
>sparc64 uses a nicer macro system to generate trampolines in asm. It
>also has a more complete list. But it's also missing some :-)
>
>Now, there is a good point to be made that we don't absolutely need to
>always sign extend. In many cases, the called function will just do a
>cmplw for example, or an and to test bits in flags, and so it looks like
>sign extension is not necessary. One could say that sign extending file
>descriptors for example isn't terribly useful
>
>But that sounds like a fragile approach to me. We don't know for sure
>what new tricks the compiler will learn for example. In fact, when
>taking the sparc64 list, I noticed that in some cases it -did- already
>sign extend file descriptors and flags .. and in some cases not.
>
>So I've spent a few hours combing through all of syscalls.h (and one
>more that seems to be missing from this file, ie, pipe2, there may be
>others) for anything using int, long or pid_t (which is signed, at least
>on our 32-bit platforms).

You might want to look at functions that take clockid_t as well.  It's also
a signed int.  We recently ran into a case of this for clock_getres on ppc64
using a 32-bit glibc.  Albiet, on a quite old kernel but looking at it briefly
it seems to still be an issue, so probably worth fixing.

josh