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1/* SPDX-License-Identifier: LGPL-2.1 OR MIT */
2/*
3 * i386 specific definitions for NOLIBC
4 * Copyright (C) 2017-2022 Willy Tarreau <w@1wt.eu>
5 */
6
7#ifndef _NOLIBC_ARCH_I386_H
8#define _NOLIBC_ARCH_I386_H
9
10#include "compiler.h"
11#include "crt.h"
12
13/* Syscalls for i386 :
14 * - mostly similar to x86_64
15 * - registers are 32-bit
16 * - syscall number is passed in eax
17 * - arguments are in ebx, ecx, edx, esi, edi, ebp respectively
18 * - all registers are preserved (except eax of course)
19 * - the system call is performed by calling int $0x80
20 * - syscall return comes in eax
21 * - the arguments are cast to long and assigned into the target registers
22 * which are then simply passed as registers to the asm code, so that we
23 * don't have to experience issues with register constraints.
24 * - the syscall number is always specified last in order to allow to force
25 * some registers before (gcc refuses a %-register at the last position).
26 *
27 * Also, i386 supports the old_select syscall if newselect is not available
28 */
29#define __ARCH_WANT_SYS_OLD_SELECT
30
31#define my_syscall0(num) \
32({ \
33 long _ret; \
34 register long _num __asm__ ("eax") = (num); \
35 \
36 __asm__ volatile ( \
37 "int $0x80\n" \
38 : "=a" (_ret) \
39 : "0"(_num) \
40 : "memory", "cc" \
41 ); \
42 _ret; \
43})
44
45#define my_syscall1(num, arg1) \
46({ \
47 long _ret; \
48 register long _num __asm__ ("eax") = (num); \
49 register long _arg1 __asm__ ("ebx") = (long)(arg1); \
50 \
51 __asm__ volatile ( \
52 "int $0x80\n" \
53 : "=a" (_ret) \
54 : "r"(_arg1), \
55 "0"(_num) \
56 : "memory", "cc" \
57 ); \
58 _ret; \
59})
60
61#define my_syscall2(num, arg1, arg2) \
62({ \
63 long _ret; \
64 register long _num __asm__ ("eax") = (num); \
65 register long _arg1 __asm__ ("ebx") = (long)(arg1); \
66 register long _arg2 __asm__ ("ecx") = (long)(arg2); \
67 \
68 __asm__ volatile ( \
69 "int $0x80\n" \
70 : "=a" (_ret) \
71 : "r"(_arg1), "r"(_arg2), \
72 "0"(_num) \
73 : "memory", "cc" \
74 ); \
75 _ret; \
76})
77
78#define my_syscall3(num, arg1, arg2, arg3) \
79({ \
80 long _ret; \
81 register long _num __asm__ ("eax") = (num); \
82 register long _arg1 __asm__ ("ebx") = (long)(arg1); \
83 register long _arg2 __asm__ ("ecx") = (long)(arg2); \
84 register long _arg3 __asm__ ("edx") = (long)(arg3); \
85 \
86 __asm__ volatile ( \
87 "int $0x80\n" \
88 : "=a" (_ret) \
89 : "r"(_arg1), "r"(_arg2), "r"(_arg3), \
90 "0"(_num) \
91 : "memory", "cc" \
92 ); \
93 _ret; \
94})
95
96#define my_syscall4(num, arg1, arg2, arg3, arg4) \
97({ \
98 long _ret; \
99 register long _num __asm__ ("eax") = (num); \
100 register long _arg1 __asm__ ("ebx") = (long)(arg1); \
101 register long _arg2 __asm__ ("ecx") = (long)(arg2); \
102 register long _arg3 __asm__ ("edx") = (long)(arg3); \
103 register long _arg4 __asm__ ("esi") = (long)(arg4); \
104 \
105 __asm__ volatile ( \
106 "int $0x80\n" \
107 : "=a" (_ret) \
108 : "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), \
109 "0"(_num) \
110 : "memory", "cc" \
111 ); \
112 _ret; \
113})
114
115#define my_syscall5(num, arg1, arg2, arg3, arg4, arg5) \
116({ \
117 long _ret; \
118 register long _num __asm__ ("eax") = (num); \
119 register long _arg1 __asm__ ("ebx") = (long)(arg1); \
120 register long _arg2 __asm__ ("ecx") = (long)(arg2); \
121 register long _arg3 __asm__ ("edx") = (long)(arg3); \
122 register long _arg4 __asm__ ("esi") = (long)(arg4); \
123 register long _arg5 __asm__ ("edi") = (long)(arg5); \
124 \
125 __asm__ volatile ( \
126 "int $0x80\n" \
127 : "=a" (_ret) \
128 : "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
129 "0"(_num) \
130 : "memory", "cc" \
131 ); \
132 _ret; \
133})
134
135#define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6) \
136({ \
137 long _eax = (long)(num); \
138 long _arg6 = (long)(arg6); /* Always in memory */ \
139 __asm__ volatile ( \
140 "pushl %[_arg6]\n\t" \
141 "pushl %%ebp\n\t" \
142 "movl 4(%%esp),%%ebp\n\t" \
143 "int $0x80\n\t" \
144 "popl %%ebp\n\t" \
145 "addl $4,%%esp\n\t" \
146 : "+a"(_eax) /* %eax */ \
147 : "b"(arg1), /* %ebx */ \
148 "c"(arg2), /* %ecx */ \
149 "d"(arg3), /* %edx */ \
150 "S"(arg4), /* %esi */ \
151 "D"(arg5), /* %edi */ \
152 [_arg6]"m"(_arg6) /* memory */ \
153 : "memory", "cc" \
154 ); \
155 _eax; \
156})
157
158/* startup code */
159/*
160 * i386 System V ABI mandates:
161 * 1) last pushed argument must be 16-byte aligned.
162 * 2) The deepest stack frame should be set to zero
163 *
164 */
165void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void)
166{
167 __asm__ volatile (
168 "xor %ebp, %ebp\n" /* zero the stack frame */
169 "mov %esp, %eax\n" /* save stack pointer to %eax, as arg1 of _start_c */
170 "add $12, %esp\n" /* avoid over-estimating after the 'and' & 'sub' below */
171 "and $-16, %esp\n" /* the %esp must be 16-byte aligned on 'call' */
172 "sub $12, %esp\n" /* sub 12 to keep it aligned after the push %eax */
173 "push %eax\n" /* push arg1 on stack to support plain stack modes too */
174 "call _start_c\n" /* transfer to c runtime */
175 "hlt\n" /* ensure it does not return */
176 );
177 __builtin_unreachable();
178}
179
180#endif /* _NOLIBC_ARCH_I386_H */