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SubjectRe: 64-syscall args on 32-bit vs syscall()
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On Sun, 2010-03-14 at 22:54 -0700, David Miller wrote:
> From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Date: Mon, 15 Mar 2010 16:18:33 +1100
>
> > Or is there any good reason -not- to do that in glibc ?
>
> The whole point of syscall() is to handle cases where the C library
> doesn't know about the system call yet.
>
> I think it's therefore very much "buyer beware".
>
> On sparc it'll never work to use the workaround you're proposing since
> we pass everything in via registers.
>
> So arch knowledge will always need to be present in these situations.

I'm not sure I follow. We also pass via register on powerpc, but the
offset introduced by the sysno argument breaks register pair alignment
which cannot be fixed up inside syscall().

However, if I change glibc's syscall to be something like

#define syscall(sysno, args...) __syscall(0 /* dummy */, sysno, args)

And make __syscall then do something like:

mr r0, r4
mr r3, r5
mr r4, r6
mr r5, r7
mr r6, r8
.../...
sc
blr

Then at least all that class of syscalls will be fixed. Of course this
has to be in glibc arch code. I was merely asking if that was something
our glibc folks would consider and whether somebody could think of a
better solution :-)

Cheers
,Ben.




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