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/* Copyright (C) 1992, 1993, 1995 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. */
/* In the Linux/ELF world, C symbols are asm symbols. */
#define NO_UNDERSCORES
/* 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; \
.globl syscall_error; \
ENTRY (name) \
movl $SYS_ify (syscall_name), %eax; \
DO_CALL (args); \
testl %eax, %eax; \
jl JUMPTARGET (syscall_error)
/* We define our own ENTRY macro because the alignment should be 16 for ELF. */
#undef ENTRY
#define ENTRY(name) \
ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (name); \
ASM_TYPE_DIRECTIVE (C_SYMBOL_NAME (name), @function) \
.align 16; \
C_LABEL (name)
/* 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 accoriding 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. */
#undef DO_CALL
#define DO_CALL(args) \
DOARGS_##args \
int $0x80; \
UNDOARGS_##args
#define DOARGS_0 /* No arguments to frob. */
#define UNDOARGS_0 /* No arguments to unfrob. */
#define _DOARGS_0(n) /* No arguments to frob. */
#define _UNDOARGS_0 /* No arguments to unfrob. */
#define DOARGS_1 movl %ebx, %edx; movl 4(%esp), %ebx; DOARGS_0
#define UNDOARGS_1 UNDOARGS_0; movl %edx, %ebx
#define _DOARGS_1(n) pushl %ebx; movl n+4(%esp), %ebx; _DOARGS_0 (n)
#define _UNDOARGS_1 _UNDOARGS_0; popl %ebx
#define DOARGS_2 movl 8(%esp), %ecx; DOARGS_1
#define UNDOARGS_2 UNDOARGS_1
#define _DOARGS_2(n) movl n(%esp), %ecx; _DOARGS_1 (n-4)
#define _UNDOARGS_2 _UNDOARGS_1
#define DOARGS_3 _DOARGS_3 (12)
#define UNDOARGS_3 _UNDOARGS_3
#define _DOARGS_3(n) movl n(%esp), %edx; _DOARGS_2 (n-4)
#define _UNDOARGS_3 _UNDOARGS_2
#define DOARGS_4 _DOARGS_4 (16)
#define UNDOARGS_4 _UNDOARGS_4
#define _DOARGS_4(n) pushl %esi; movl n+4(%esp), %esi; _DOARGS_3 (n)
#define _UNDOARGS_4 _UNDOARGS_3; popl %esi
#define DOARGS_5 _DOARGS_5 (20)
#define UNDOARGS_5 _UNDOARGS_5
#define _DOARGS_5(n) pushl %edi; movl n+4(%esp), %edi; _DOARGS_4 (n)
#define _UNDOARGS_5 _UNDOARGS_4; popl %edi
#endif /* ASSEMBLER */
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