Ralf Baechle wrote:
> On Mon, Dec 15, 2008 at 09:57:24PM +0100, Gerd Hoffmann wrote:
>
>>> It fixes the alignment issue but still won't work; on MIPS 32-bit userspace
>>> will pass the 64-bit argument in two registers but the 64-bit kernel code
>>> will assume it to be passed in a single registers. It'd be ugly but passing
>>> a pointer to a 64-bit argument would solve the issue; something like this:
>>>
>>> sys_preadv(unsigned long fd, const struct iovec __user *vec,
>>> unsigned long vlen, loff_t __user *pos);
>>> compat_sys_preadv(unsigned long fd, const struct compat_iovec __user *vec,
>>> unsigned long vlen, loff_t __user *pos);
>> Suggestion from the s390 front was to explicitly pass high and low part
>> of pos as two arguments. A bit ugly too, but should work fine as well
>> and it avoids the user pointer dereference. What do you think about this?
>
> That's what the wrapper which you deleted, was doing ;-) So yes, I like
> it.
Yep, but I'm trying to find a way to have it work without per-arch
wrappers ...
> It just raises one new problem, endianess - are arguments being passed
> as low/high or high/low? On MIPS we've been solving the issue with the
> merge_64() macro which is defined depending on the byte order:
>
> #ifdef __MIPSEB__
> #define merge_64(r1, r2) ((((r1) & 0xffffffffUL) << 32) + ((r2) & 0xffffffffUL))
> #endif
> #ifdef __MIPSEL__
> #define merge_64(r1, r2) ((((r2) & 0xffffffffUL) << 32) + ((r1) & 0xffffffffUL))
> #endif
>
> The actual syscall wrapper could use it like:
>
> asmlinkage int compat_sys_pwritev(unsigned long fd,
> const struct compat_iovec __user *vec,
> unsigned a3, unsigned a4, unsigned long vlen)
> {
> loff_t offset = merge_64(a3, a4);
> ...
i.e. the ordering of the splitted argument depends on the os endianness?
What is the reason for this?
I'd prefer to have the ordering coded explicitly instead, like this:
asmlinkage int compat_sys_pwritev(unsigned long fd,
const struct compat_iovec __user *vec, unsigned long vlen,
unsigned pos_low, unsigned pos_high)
{
loff_t pos = pos_low | (loff_t)pos_high << 32;
[ ... ]
cheers,
Gerd
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