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glibc/sysdeps/unix/sysv/linux/i386/sysdep.h

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/* Copyright (C) 1992, 93, 95, 96 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper, <drepper@gnu.ai.mit.edu>, August 1995.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If
not, write to the Free Software Foundation, Inc., 675 Mass Ave,
Cambridge, MA 02139, USA. */
#ifndef _LINUX_I386_SYSDEP_H
#define _LINUX_I386_SYSDEP_H 1
/* There is some commonality. */
#include <sysdeps/unix/i386/sysdep.h>
/* For Linux we can use the system call table in the header file
/usr/include/asm/unistd.h
of the kernel. But these symbols do not follow the SYS_* syntax
so we have to redefine the `SYS_ify' macro here. */
#undef SYS_ify
#ifdef __STDC__
# define SYS_ify(syscall_name) __NR_##syscall_name
#else
# define SYS_ify(syscall_name) __NR_/**/syscall_name
#endif
#ifdef ASSEMBLER
/* Linux uses a negative return value to indicate syscall errors, unlike
most Unices, which use the condition codes' carry flag. */
#undef PSEUDO
#define PSEUDO(name, syscall_name, args) \
.text; \
SYSCALL_ERROR_HANDLER \
ENTRY (name) \
DO_CALL (args, syscall_name); \
testl %eax, %eax; \
jl syscall_error;
#ifndef PIC
#define SYSCALL_ERROR_HANDLER /* Nothing here; code in sysdep.S is used. */
#else
/* Store (- %eax) into errno through the GOT. */
#ifdef _LIBC_REENTRANT
#define SYSCALL_ERROR_HANDLER \
.type syscall_error,@function; \
syscall_error: \
pushl %ebx; \
call 0f; \
0:popl %ebx; \
xorl %edx, %edx; \
addl $_GLOBAL_OFFSET_TABLE_+[.-0b], %ebx; \
subl %eax, %edx; \
movl errno@GOT(%ebx), %ecx; \
movl %edx, (%ecx); \
pushl %edx; \
call __errno_location@PLT; \
popl %ecx; \
popl %ebx; \
movl %ecx, (%eax); \
movl $-1, %eax; \
ret;
#else
#define SYSCALL_ERROR_HANDLER \
.type syscall_error,@function; \
syscall_error: \
call 0f; \
0:popl %ecx; \
xorl %edx, %edx; \
addl $_GLOBAL_OFFSET_TABLE_+[.-0b], %ecx; \
subl %eax, %edx; \
movl errno@GOT(%ecx), %ecx; \
movl %edx, (%ecx); \
movl $-1, %eax; \
ret;
#endif /* _LIBC_REENTRANT */
#endif /* PIC */
/* Linux takes system call arguments in registers:
syscall number %eax call-clobbered
arg 1 %ebx call-saved
arg 2 %ecx call-clobbered
arg 3 %edx call-clobbered
arg 4 %esi call-saved
arg 5 %edi call-saved
The stack layout upon entering the function is:
20(%esp) Arg# 5
16(%esp) Arg# 4
12(%esp) Arg# 3
8(%esp) Arg# 2
4(%esp) Arg# 1
(%esp) Return address
(Of course a function with say 3 arguments does not have entries for
arguments 4 and 5.)
The following code tries hard to be optimal. A general assuption
(which is true according to the data books I have) is that
2 * xchg is more expensive than pushl + movl + popl
Beside this a neat trick is used. The calling conventions for Linux
tell that among the registers used for parameters %ecx and %edx need
not be saved. Beside this we may clobber this registers even when
they are not used for parameter passing.
As a result one can see below that we save the content of the %ebx
register in the %edx register when we have less than 3 arguments
(2 * movl is less expensive than pushl + popl).
Second unlike for the other registers we don't save the content of
%ecx and %edx when we have than 1 and 2 registers resp.
The code below might look a bit long but we have to take care for
the pipelined processors (i586 and up). Here the `pushl' and `popl'
instructions are marked as NP (not pairable) but the exception is
two consecutive of these instruction. This gives no penalty on
i386 and i486 processors though. */
#undef DO_CALL
#define DO_CALL(args, syscall_name) \
PUSHARGS_##args \
DOARGS_##args \
movl $SYS_ify (syscall_name), %eax; \
int $0x80 \
POPARGS_##args
#define PUSHARGS_0 /* No arguments to push. */
#define DOARGS_0 /* No arguments to frob. */
#define POPARGS_0 /* No arguments to pop. */
#define _PUSHARGS_0 /* No arguments to push. */
#define _DOARGS_0(n) /* No arguments to frob. */
#define _POPARGS_0 /* No arguments to pop. */
#define PUSHARGS_1 movl %ebx, %edx; PUSHARGS_0
#define DOARGS_1 _DOARGS_1 (4)
#define POPARGS_1 POPARGS_0; movl %edx, %ebx
#define _PUSHARGS_1 pushl %ebx; _PUSHARGS_0
#define _DOARGS_1(n) movl n(%esp), %ebx; _DOARGS_0(n-4)
#define _POPARGS_1 _POPARGS_0; popl %ebx
#define PUSHARGS_2 PUSHARGS_1
#define DOARGS_2 _DOARGS_2 (8)
#define POPARGS_2 POPARGS_1
#define _PUSHARGS_2 _PUSHARGS_1
#define _DOARGS_2(n) movl n(%esp), %ecx; _DOARGS_1 (n-4)
#define _POPARGS_2 _POPARGS_1
#define PUSHARGS_3 _PUSHARGS_2
#define DOARGS_3 _DOARGS_3 (16)
#define POPARGS_3 _POPARGS_3
#define _PUSHARGS_3 _PUSHARGS_2
#define _DOARGS_3(n) movl n(%esp), %edx; _DOARGS_2 (n-4)
#define _POPARGS_3 _POPARGS_2
#define PUSHARGS_4 _PUSHARGS_4
#define DOARGS_4 _DOARGS_4 (24)
#define POPARGS_4 _POPARGS_4
#define _PUSHARGS_4 pushl %esi; _PUSHARGS_3
#define _DOARGS_4(n) movl n(%esp), %esi; _DOARGS_3 (n-4)
#define _POPARGS_4 _POPARGS_3; popl %esi
#define PUSHARGS_5 _PUSHARGS_5
#define DOARGS_5 _DOARGS_5 (32)
#define POPARGS_5 _POPARGS_5
#define _PUSHARGS_5 pushl %edi; _PUSHARGS_4
#define _DOARGS_5(n) movl n(%esp), %edi; _DOARGS_4 (n-4)
#define _POPARGS_5 _POPARGS_4; popl %edi
#endif /* ASSEMBLER */
#endif /* linux/i386/sysdep.h */
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