[PATCH] Use SYSCALL_LL[64] to pass 64-bit value [BZ #20349]

[H.J. Lu]

On Mon, Jul 11, 2016 at 2:04 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Mon, Jul 11, 2016 at 1:36 PM, Chris Metcalf <cmetcalf@mellanox.com> wrote:
>> On 7/11/2016 3:26 PM, H.J. Lu wrote:
>>>
>>> SYSCALL_LL/SYSCALL_LL64 should be used to pass 64-bit value to system
>>> calls.
>>
>>
>> What problem are you trying to solve?
>>
>> SYSCALL_LL and LO_HI_LONG are different on big-endian systems.  In this
>> case, LO_HI_LONG is correct, since the kernel API is "unsigned long pos_l,
>> unsigned long pos_h".  SYSCALL_LL won't do the right thing.
>>
>> __ALIGNMENT_ARG introduces an extra dummy arguments to be inserted before
>> a 64-bit value split into two 32-bit registers, if required by the platform.
>> Since preadv/pwritev explicitly use split arguments to construct a 64-bit
>> loff_t, __ALIGNMENT_ARG will just add a random inappropriate dummy arg
>> to an API that doesn't need one.
>>
>> I reviewed the casting for LO_HI_LONG and it looks OK; I initially was
>> wondering whether losing the "val >> 31, val" semantics from SYSCALL_LL()
>> might have been problematic, but it seems like LO_HI_LONG should generate
>> the same results.
>>
>
> /* Provide a macro to pass the off{64}_t argument on p{readv,writev}{64}.  */
> #define LO_HI_LONG(val) \
>  (long) (val), \
>  (long) (((uint64_t) (val)) >> 32)
>
> is wrong for __ASSUME_WORDSIZE64_ILP32 platform.
>

I am testing this.


-- 
H.J.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 0001-X86-64-Define-LO_HI_LONG-to-skip-pos_h-BZ-20349.patch
Type: text/x-patch
Size: 1103 bytes
Desc: not available
URL: <http://sourceware.org/pipermail/libc-alpha/attachments/20160711/1d4ebfb5/attachment.bin>