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  */
_start(void)165 void __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 */
181