[systemd-devel] [PATCH] Fix broken syscall(__NR_fanotify_mark... on 32bit mips.

[Lennart Poettering]

On Wed, 20.04.11 11:43, David Daney (ddaney at caviumnetworks.com) wrote:

> 
> On 04/20/2011 11:34 AM, Lennart Poettering wrote:
> >On Wed, 20.04.11 11:19, David Daney (ddaney at caviumnetworks.com) wrote:
> >
> >>
> >>On 04/20/2011 11:09 AM, Lennart Poettering wrote:
> >>>On Wed, 20.04.11 10:36, David Daney (ddaney at caviumnetworks.com) wrote:
> >>>
> >>>>You would have to do something like this (untested):
> >>>>
> >>>>int foo_fanotify_mark(int fanotify_fd, unsigned int flags, u64 mask,
> >>>>int dfd, const char  __user * pathname)
> >>>>{
> >>>>	u32 mask_low = (u32)mask;
> >>>>	u32 mask_high = (u32)(mask>>   32);
> >>>>
> >>>>	return syscall(4337, fanotify_fd, flags, mask_low, mask_high, dfd,
> >>>>pathname);
> >>>>
> >>>>}
> >>>>
> >>>>The order of mask_low, mask_high in the syscall argument list
> >>>>depends on the endianness.  Figuring out the correct order is left
> >>>>as an exercise for the reader.
> >>>
> >>>That's basically the same patch as this one, right?
> >>>
> >>>http://lists.freedesktop.org/archives/systemd-devel/attachments/20110420/be2d393b/attachment.obj
> >>>
> >>
> >>It looks like it might do the same thing.  Someone should try it on
> >>an o32 MIPS userland running on a mips64 kernel.
> >>
> >>I think the behavior of the union thing is undefined, but should
> >>work on GCC.
> >
> >Hmm, but unions is the official C99 way to do these things, isn't it?
> >Instead of doing casts here and there which create aliasing probs?
> >
> >Any comment whether this will break non-MIPS 32bit archs, like x86?
> 
> It would break the MIPS n32 ABI userspace.
> 
> On MIPS n32 we are still __LP64__, but 64-bit values are passed in a
> single register.
> 
> I expect that the experimental x86_64 x32 ABI would suffer the same way.
> 
> So the change would have to be gated by ABI rather than __LP64__

Hmm, OK. Do you happen to know which predefined userspace macro we
should check against for the o32 ABI?

There seems to be __mips__, but that probably covers both ABIs?

Lennart

-- 
Lennart Poettering - Red Hat, Inc.