Re: [PATCH 3/6] i386: Remove syscall assembly codes with 6 arguments

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

On Fri, Aug 14, 2015 at 10:34 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Fri, Aug 14, 2015 at 5:17 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> OK for master?
>>
>> H.J.
>> ---
>> This patch removes i386 assembly implementation for epoll_wait, mmap,
>> mmap64, semtimeop now that i386 have 6 argument syscall support from
>> C code and GCC 5 can inline syscalls with 6 argument.  We also compile
>> epoll_pwait.c, mmap.c, mmap64.c and semtimedop.c with -fomit-frame-pointer
>> since %ebp may be used to pass the 6th argument to syscall.
>>
>> Fo sysdeps/unix/sysv/linux/i386/mmap.c, with -O2 -march=i686
>> -mtune=generic, GCC 5.2 now generates:
>>
>> <__mmap>:
>>    0:   sub    $0x10,%esp
>>    3:   mov    0x28(%esp),%eax
>>    7:   mov    %ebx,(%esp)
>>    a:   mov    0x18(%esp),%ecx
>>    e:   mov    %esi,0x4(%esp)
>>   12:   mov    0x14(%esp),%ebx
>>   16:   mov    %edi,0x8(%esp)
>>   1a:   mov    0x1c(%esp),%edx
>>   1e:   test   $0xfff,%eax
>>   23:   mov    0x20(%esp),%esi
>>   27:   mov    %ebp,0xc(%esp)
>>   2b:   mov    0x24(%esp),%edi
>>   2f:   jne    60 <__mmap+0x60>
>>   31:   sar    $0xc,%eax
>>   34:   mov    %eax,%ebp
>>   36:   mov    $0xc0,%eax
>>   3b:   call   *%gs:0x10
>>   42:   cmp    $0xfffff000,%eax
>>   47:   ja     65 <__mmap+0x65>
>>   49:   mov    (%esp),%ebx
>>   4c:   mov    0x4(%esp),%esi
>>   50:   mov    0x8(%esp),%edi
>>   54:   mov    0xc(%esp),%ebp
>>   58:   add    $0x10,%esp
>>   5b:   ret
>>   5c:   lea    0x0(%esi,%eiz,1),%esi
>>   60:   mov    $0xffffffea,%eax
>>   65:   mov    (%esp),%ebx
>>   68:   mov    0x4(%esp),%esi
>>   6c:   mov    0x8(%esp),%edi
>>   70:   mov    0xc(%esp),%ebp
>>   74:   add    $0x10,%esp
>>   77:   jmp    78 <__mmap+0x78> 78: R_386_PC32  __syscall_error
>>
>> vs sysdeps/unix/sysv/linux/i386/mmap.S:
>>
>> <__mmap>:
>>    0:   push   %ebp
>>    1:   push   %ebx
>>    2:   push   %esi
>>    3:   push   %edi
>>    4:   mov    0x14(%esp),%ebx
>>    8:   mov    0x18(%esp),%ecx
>>    c:   mov    0x1c(%esp),%edx
>>   10:   mov    0x20(%esp),%esi
>>   14:   mov    0x24(%esp),%edi
>>   18:   mov    0x28(%esp),%ebp
>>   1c:   test   $0xfff,%ebp
>>   22:   mov    $0xffffffea,%eax
>>   27:   jne    38 <__mmap+0x38>
>>   29:   shr    $0xc,%ebp
>>   2c:   mov    $0xc0,%eax
>>   31:   call   *%gs:0x10
>>   38:   pop    %edi
>>   39:   pop    %esi
>>   3a:   pop    %ebx
>>   3b:   pop    %ebp
>>   3c:   cmp    $0xfffff000,%eax
>>   41:   ja     44 <__mmap+0x44>
>>   43:   ret
>>   44:   call   45 <__mmap+0x45> 45: R_386_PC32  __x86.get_pc_thunk.cx
>>   49:   add    $0x2,%ecx        4b: R_386_GOTPC _GLOBAL_OFFSET_TABLE_
>>   4f:   mov    0x0(%ecx),%ecx   51: R_386_TLS_GOTIE     __libc_errno
>>   55:   neg    %eax
>>   57:   mov    %eax,%gs:(%ecx)
>>   5a:   or     $0xffffffff,%eax
>>   5d:   ret
>>
>> The C version has:
>>
>>    3:   mov    0x28(%esp),%eax
>> ...
>>   1e:   test   $0xfff,%eax
>> ...
>>   31:   sar    $0xc,%eax
>>   34:   mov    %eax,%ebp
>>
>> is due to missing $ebx register constraint for inline asm.  We have
>> to use "r" constraint with
>>
>> register unsigned int _a6 asm ("ebp") = (unsigned int) (arg6);
>>
>> and compiler chose %eax for offset (arg6) in
>>
>>   if (offset & ((1 << MMAP_PAGE_SHIFT) - 1))
>>
>>         * sysdeps/unix/sysv/linux/i386/Makefile (CFLAGS-epoll_pwait.c):
>>         Add -fomit-frame-pointer.
>>         (CFLAGS-mmap.c): Likewise.
>>         (CFLAGS-mmap64.c): Likewise.
>>         (CFLAGS-semtimedop.c): Likewise.
>>         * sysdeps/unix/sysv/linux/i386/mmap.c: New file.
>>         * sysdeps/unix/sysv/linux/i386/epoll_pwait.S: Remove file.
>>         * sysdeps/unix/sysv/linux/i386/mmap.S: Likewise.
>>         * sysdeps/unix/sysv/linux/i386/mmap64.S: Likewise.
>>         * sysdeps/unix/sysv/linux/i386/semtimedop.S: Likewise.
>
> Here is the patch for updated INLINE_SYSCALL_RETURN and
> INLINE_SYSCALL_ERROR_RETURN.  OK for master?

I will check it in next Monday if there are no objections.


-- 
H.J.