Re: [PATCH] [BZ #19371] Properly handle x32 syscall

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Wed, Dec 16, 2015 at 8:58 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Wed, Dec 16, 2015 at 8:54 AM, Adhemerval Zanella
> <adhemerval.zanella@linaro.org> wrote:
>>
>>
>> On 16-12-2015 14:52, H.J. Lu wrote:
>>> On Wed, Dec 16, 2015 at 8:48 AM, Dmitry V. Levin <ldv@altlinux.org> wrote:
>>>> On Wed, Dec 16, 2015 at 07:01:39AM -0800, H.J. Lu wrote:
>>>>> X32 syscall() may return 64-bit integer as lseek, time and times.  Its
>>>>> return type should be __syscall_slong_t instead of long int.  We need
>>>>> to properly return 64-bit error value.
>>>> [...]
>>>>> +#include <sysdep.h>
>>>>> +
>>>>> +/* Return -1LL in a full 64 bits.  */
>>>>> +#undef SYSCALL_ERROR_HANDLER
>>>>> +#define SYSCALL_ERROR_HANDLER        \
>>>>> +0:                           \
>>>>> +     SYSCALL_SET_ERRNO;      \
>>>>> +     orq $-1, %rax;          \
>>>>> +     ret;
>>>>> +
>>>>> +/* Always use our own error handler.  */
>>>>> +#undef SYSCALL_ERROR_LABEL
>>>>> +#define SYSCALL_ERROR_LABEL 0f
>>>>> +
>>>>> +#include <sysdeps/unix/sysv/linux/x86_64/syscall.S>
>>>>
>>>> While this looks technically OK, I don't understand why RAX_LP is used
>>>> at all in default SYSCALL_ERROR_HANDLER in place for rax.  Everything
>>>> would be simpler if glibc finally admitted that return code of any
>>>> x32 linux syscall is stored in %rax and not in %eax.
>>>
>>> Only 3 system calls return 64-bit value.  %eax is one-byte shorter.
>>>
>>
>> I still fail the see the performance gains over the re-engineering and
>> code duplication required to avoid make the syscall return 64-bit values.
>
> What code duplication?
>

The whole point of x32 is it is ILP32.  Some system calls return
64-bit is just an exception.

-- 
H.J.