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

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

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.