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

[Lennart Poettering]

On Wed, 20.04.11 09:15, fykcee1 at gmail.com (fykcee1 at gmail.com) wrote:

> 
> 2011/4/20 Lennart Poettering <lennart at poettering.net>
> >
> > On Thu, 14.04.11 17:34, fykcee1 at gmail.com (fykcee1 at gmail.com) wrote:
> >
> > > diff --git a/src/missing.h b/src/missing.h
> > > index 35e209f..b367831 100644
> > > --- a/src/missing.h
> > > +++ b/src/missing.h
> > > @@ -125,7 +125,12 @@ static inline int fanotify_init(unsigned int flags, unsigned int event_f_flags)
> > >
> > >  static inline int fanotify_mark(int fanotify_fd, unsigned int flags, uint64_t mask,
> > >                                  int dfd, const char *pathname) {
> > > -        return syscall(__NR_fanotify_mark, fanotify_fd, flags, mask, dfd, pathname);
> > > +        if (sizeof(void *) == 4)
> > > +                return syscall(__NR_fanotify_mark, fanotify_fd, flags,
> > > +                               *((uint32_t *) &mask), *((uint32_t *) &mask + 1),
> > > +                               dfd, pathname);
> > > +        else /* 64bit */
> > > +                return syscall(__NR_fanotify_mark, fanotify_fd, flags, mask, dfd, pathname);
> > >  }
> > >
> > >  #ifndef BTRFS_IOCTL_MAGIC
> >
> > Hmm, wouldn't this break x86-32?
> It works fine on my asus laptop with a 32bit CPU Pentium-M.
> 
> We pass two 32bit arguments instead of one 64bit argument. syscall()
> doesn't know the prototype, I guess it will only fetch 9 native-width
> arguments(1 syscall number + 8 parameters) from the stack. Aurelien,
> am I right?

Hmm, I am not sure I understand this? How is it possible that both ways
work on x86? There must be quite a difference between passing 6 or 7
arguments to syscall.

Or are you suggesting that the current invocation is broken even on x86,
just doesn't become visible since only the lower 32 bit of "mask" are
used?

> > Also, I'd very much prefer if this could be done with compile time
> > checks instead of "if". i.e.
> >
> > #ifdef __mips__
> Actually it's not only related to mips, but also to all arch that
> force 64-aligned for 64bit argument (Aurelien said this can also be
> reproduced on powerpc and arm). So what I want is:
> #if PTR_BYTES == 4
> ....
> 
> I tried to find some macro like PTR_BYTES or PTR_SIZE, but failed. Is
> such macro available?

I think "#ifndef __LP64__" does what you want?

Lennart

-- 
Lennart Poettering - Red Hat, Inc.