1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
|
/* Copyright (C) 1992, 93, 95, 96, 97, 98 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., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, 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
#define SYS_ify(syscall_name) __NR_##syscall_name
/* ELF-like local names start with `.L'. */
#undef L
#define L(name) .L##name
#ifdef ASSEMBLER
/* Linux uses a negative return value to indicate syscall errors,
unlike most Unices, which use the condition codes' carry flag.
Since version 2.1 the return value of a system call might be
negative even if the call succeeded. E.g., the `lseek' system call
might return a large offset. Therefore we must not anymore test
for < 0, but test for a real error by making sure the value in %eax
is a real error number. Linus said he will make sure the no syscall
returns a value in -1 .. -4095 as a valid result so we can savely
test with -4095. */
#undef PSEUDO
#define PSEUDO(name, syscall_name, args) \
.text; \
ENTRY (name) \
DO_CALL (args, syscall_name); \
cmpl $-4095, %eax; \
jae syscall_error; \
L(pseudo_end):
#undef PSEUDO_END
#define PSEUDO_END(name) \
SYSCALL_ERROR_HANDLER \
END (name)
#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; \
pushl %edx; \
call __errno_location@PLT; \
popl %ecx; \
popl %ebx; \
movl %ecx, (%eax); \
movl $-1, %eax; \
jmp L(pseudo_end); \
.size syscall_error,.-syscall_error;
/* A quick note: it is assumed that the call to `__errno_location' does
not modify the stack! */
#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; \
jmp L(pseudo_end); \
.size syscall_error,.-syscall_error;
#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 assumption
(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 more 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 */
|
