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Re: [WIP] BZ #14361: POSIX vs. BSD and the `ioctl' interface.
On Wed, Jul 25, 2012 at 07:48:55PM -0400, Chris Metcalf wrote:
> On 7/25/2012 5:39 PM, Roland McGrath wrote:
> > The tilegx and mipsn64 code to explicitly sign-extend seems
> > misguided to me. As Linus said in bugzilla, Linux always treats it
> > as a 32-bit quantity so it really should not care at all whether it
> > was sign-extended to 64 bits or not.
>
> The problem is that for kernels not configured with HAVE_SYSCALL_WRAPPERS,
> calling ioctl() with a value that has bit 31 set will result in a value
> that does not compare equal within the kernel: the passed-in value will
> have zero high bits (since the ioctl argument was prototyped as a long) but
> the kernel constant that the comparison is done against will be
> sign-extended (since it's prototyped as an int). So the comparison fails.
> This is true for both tilegx and mipsn64 as far as I know.
Why, when this issue first came up, could the kernel developers not be
bothered to add a simple (int) cast to the argument before it gets
used in kernelspace? That would have fixed the whole problem and made
it so fixing the userspace would be an _independent_ issue to address
rather than something with ugly kernel interaction, and it would also
have fixed hypothetical programs that use syscall(SYS_ioctl, ...) to
make ioctls...
Rich