1 /* SPDX-License-Identifier: LGPL-2.1 OR MIT */
2 /*
3 * x86_64 specific definitions for NOLIBC
4 * Copyright (C) 2017-2022 Willy Tarreau <w@1wt.eu>
5 */
6
7 #ifndef _NOLIBC_ARCH_X86_64_H
8 #define _NOLIBC_ARCH_X86_64_H
9
10 #include "compiler.h"
11 #include "crt.h"
12
13 /* Syscalls for x86_64 :
14 * - registers are 64-bit
15 * - syscall number is passed in rax
16 * - arguments are in rdi, rsi, rdx, r10, r8, r9 respectively
17 * - the system call is performed by calling the syscall instruction
18 * - syscall return comes in rax
19 * - rcx and r11 are clobbered, others are preserved.
20 * - the arguments are cast to long and assigned into the target registers
21 * which are then simply passed as registers to the asm code, so that we
22 * don't have to experience issues with register constraints.
23 * - the syscall number is always specified last in order to allow to force
24 * some registers before (gcc refuses a %-register at the last position).
25 * - see also x86-64 ABI section A.2 AMD64 Linux Kernel Conventions, A.2.1
26 * Calling Conventions.
27 *
28 * Link x86-64 ABI: https://gitlab.com/x86-psABIs/x86-64-ABI/-/wikis/home
29 *
30 */
31
32 #define my_syscall0(num) \
33 ({ \
34 long _ret; \
35 register long _num __asm__ ("rax") = (num); \
36 \
37 __asm__ volatile ( \
38 "syscall\n" \
39 : "=a"(_ret) \
40 : "0"(_num) \
41 : "rcx", "r11", "memory", "cc" \
42 ); \
43 _ret; \
44 })
45
46 #define my_syscall1(num, arg1) \
47 ({ \
48 long _ret; \
49 register long _num __asm__ ("rax") = (num); \
50 register long _arg1 __asm__ ("rdi") = (long)(arg1); \
51 \
52 __asm__ volatile ( \
53 "syscall\n" \
54 : "=a"(_ret) \
55 : "r"(_arg1), \
56 "0"(_num) \
57 : "rcx", "r11", "memory", "cc" \
58 ); \
59 _ret; \
60 })
61
62 #define my_syscall2(num, arg1, arg2) \
63 ({ \
64 long _ret; \
65 register long _num __asm__ ("rax") = (num); \
66 register long _arg1 __asm__ ("rdi") = (long)(arg1); \
67 register long _arg2 __asm__ ("rsi") = (long)(arg2); \
68 \
69 __asm__ volatile ( \
70 "syscall\n" \
71 : "=a"(_ret) \
72 : "r"(_arg1), "r"(_arg2), \
73 "0"(_num) \
74 : "rcx", "r11", "memory", "cc" \
75 ); \
76 _ret; \
77 })
78
79 #define my_syscall3(num, arg1, arg2, arg3) \
80 ({ \
81 long _ret; \
82 register long _num __asm__ ("rax") = (num); \
83 register long _arg1 __asm__ ("rdi") = (long)(arg1); \
84 register long _arg2 __asm__ ("rsi") = (long)(arg2); \
85 register long _arg3 __asm__ ("rdx") = (long)(arg3); \
86 \
87 __asm__ volatile ( \
88 "syscall\n" \
89 : "=a"(_ret) \
90 : "r"(_arg1), "r"(_arg2), "r"(_arg3), \
91 "0"(_num) \
92 : "rcx", "r11", "memory", "cc" \
93 ); \
94 _ret; \
95 })
96
97 #define my_syscall4(num, arg1, arg2, arg3, arg4) \
98 ({ \
99 long _ret; \
100 register long _num __asm__ ("rax") = (num); \
101 register long _arg1 __asm__ ("rdi") = (long)(arg1); \
102 register long _arg2 __asm__ ("rsi") = (long)(arg2); \
103 register long _arg3 __asm__ ("rdx") = (long)(arg3); \
104 register long _arg4 __asm__ ("r10") = (long)(arg4); \
105 \
106 __asm__ volatile ( \
107 "syscall\n" \
108 : "=a"(_ret) \
109 : "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), \
110 "0"(_num) \
111 : "rcx", "r11", "memory", "cc" \
112 ); \
113 _ret; \
114 })
115
116 #define my_syscall5(num, arg1, arg2, arg3, arg4, arg5) \
117 ({ \
118 long _ret; \
119 register long _num __asm__ ("rax") = (num); \
120 register long _arg1 __asm__ ("rdi") = (long)(arg1); \
121 register long _arg2 __asm__ ("rsi") = (long)(arg2); \
122 register long _arg3 __asm__ ("rdx") = (long)(arg3); \
123 register long _arg4 __asm__ ("r10") = (long)(arg4); \
124 register long _arg5 __asm__ ("r8") = (long)(arg5); \
125 \
126 __asm__ volatile ( \
127 "syscall\n" \
128 : "=a"(_ret) \
129 : "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
130 "0"(_num) \
131 : "rcx", "r11", "memory", "cc" \
132 ); \
133 _ret; \
134 })
135
136 #define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6) \
137 ({ \
138 long _ret; \
139 register long _num __asm__ ("rax") = (num); \
140 register long _arg1 __asm__ ("rdi") = (long)(arg1); \
141 register long _arg2 __asm__ ("rsi") = (long)(arg2); \
142 register long _arg3 __asm__ ("rdx") = (long)(arg3); \
143 register long _arg4 __asm__ ("r10") = (long)(arg4); \
144 register long _arg5 __asm__ ("r8") = (long)(arg5); \
145 register long _arg6 __asm__ ("r9") = (long)(arg6); \
146 \
147 __asm__ volatile ( \
148 "syscall\n" \
149 : "=a"(_ret) \
150 : "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
151 "r"(_arg6), "0"(_num) \
152 : "rcx", "r11", "memory", "cc" \
153 ); \
154 _ret; \
155 })
156
157 /* startup code */
158 /*
159 * x86-64 System V ABI mandates:
160 * 1) %rsp must be 16-byte aligned right before the function call.
161 * 2) The deepest stack frame should be zero (the %rbp).
162 *
163 */
_start(void)164 void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void)
165 {
166 __asm__ volatile (
167 "xor %ebp, %ebp\n" /* zero the stack frame */
168 "mov %rsp, %rdi\n" /* save stack pointer to %rdi, as arg1 of _start_c */
169 "and $-16, %rsp\n" /* %rsp must be 16-byte aligned before call */
170 "call _start_c\n" /* transfer to c runtime */
171 "hlt\n" /* ensure it does not return */
172 );
173 __builtin_unreachable();
174 }
175
176 #endif /* _NOLIBC_ARCH_X86_64_H */
177
