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 /* The struct returned by the stat() syscall, equivalent to stat64(). The
11  * syscall returns 116 bytes and stops in the middle of __unused.
12  */
13 struct sys_stat_struct {
14 	unsigned long st_dev;
15 	unsigned long st_ino;
16 	unsigned long st_nlink;
17 	unsigned int  st_mode;
18 	unsigned int  st_uid;
19 
20 	unsigned int  st_gid;
21 	unsigned int  __pad0;
22 	unsigned long st_rdev;
23 	long          st_size;
24 	long          st_blksize;
25 
26 	long          st_blocks;
27 	unsigned long st_atime;
28 	unsigned long st_atime_nsec;
29 	unsigned long st_mtime;
30 
31 	unsigned long st_mtime_nsec;
32 	unsigned long st_ctime;
33 	unsigned long st_ctime_nsec;
34 	long          __unused[3];
35 };
36 
37 /* Syscalls for x86_64 :
38  *   - registers are 64-bit
39  *   - syscall number is passed in rax
40  *   - arguments are in rdi, rsi, rdx, r10, r8, r9 respectively
41  *   - the system call is performed by calling the syscall instruction
42  *   - syscall return comes in rax
43  *   - rcx and r11 are clobbered, others are preserved.
44  *   - the arguments are cast to long and assigned into the target registers
45  *     which are then simply passed as registers to the asm code, so that we
46  *     don't have to experience issues with register constraints.
47  *   - the syscall number is always specified last in order to allow to force
48  *     some registers before (gcc refuses a %-register at the last position).
49  *   - see also x86-64 ABI section A.2 AMD64 Linux Kernel Conventions, A.2.1
50  *     Calling Conventions.
51  *
52  * Link x86-64 ABI: https://gitlab.com/x86-psABIs/x86-64-ABI/-/wikis/home
53  *
54  */
55 
56 #define my_syscall0(num)                                                      \
57 ({                                                                            \
58 	long _ret;                                                            \
59 	register long _num  __asm__ ("rax") = (num);                          \
60 	                                                                      \
61 	__asm__  volatile (                                                   \
62 		"syscall\n"                                                   \
63 		: "=a"(_ret)                                                  \
64 		: "0"(_num)                                                   \
65 		: "rcx", "r11", "memory", "cc"                                \
66 	);                                                                    \
67 	_ret;                                                                 \
68 })
69 
70 #define my_syscall1(num, arg1)                                                \
71 ({                                                                            \
72 	long _ret;                                                            \
73 	register long _num  __asm__ ("rax") = (num);                          \
74 	register long _arg1 __asm__ ("rdi") = (long)(arg1);                   \
75 	                                                                      \
76 	__asm__  volatile (                                                   \
77 		"syscall\n"                                                   \
78 		: "=a"(_ret)                                                  \
79 		: "r"(_arg1),                                                 \
80 		  "0"(_num)                                                   \
81 		: "rcx", "r11", "memory", "cc"                                \
82 	);                                                                    \
83 	_ret;                                                                 \
84 })
85 
86 #define my_syscall2(num, arg1, arg2)                                          \
87 ({                                                                            \
88 	long _ret;                                                            \
89 	register long _num  __asm__ ("rax") = (num);                          \
90 	register long _arg1 __asm__ ("rdi") = (long)(arg1);                   \
91 	register long _arg2 __asm__ ("rsi") = (long)(arg2);                   \
92 	                                                                      \
93 	__asm__  volatile (                                                   \
94 		"syscall\n"                                                   \
95 		: "=a"(_ret)                                                  \
96 		: "r"(_arg1), "r"(_arg2),                                     \
97 		  "0"(_num)                                                   \
98 		: "rcx", "r11", "memory", "cc"                                \
99 	);                                                                    \
100 	_ret;                                                                 \
101 })
102 
103 #define my_syscall3(num, arg1, arg2, arg3)                                    \
104 ({                                                                            \
105 	long _ret;                                                            \
106 	register long _num  __asm__ ("rax") = (num);                          \
107 	register long _arg1 __asm__ ("rdi") = (long)(arg1);                   \
108 	register long _arg2 __asm__ ("rsi") = (long)(arg2);                   \
109 	register long _arg3 __asm__ ("rdx") = (long)(arg3);                   \
110 	                                                                      \
111 	__asm__  volatile (                                                   \
112 		"syscall\n"                                                   \
113 		: "=a"(_ret)                                                  \
114 		: "r"(_arg1), "r"(_arg2), "r"(_arg3),                         \
115 		  "0"(_num)                                                   \
116 		: "rcx", "r11", "memory", "cc"                                \
117 	);                                                                    \
118 	_ret;                                                                 \
119 })
120 
121 #define my_syscall4(num, arg1, arg2, arg3, arg4)                              \
122 ({                                                                            \
123 	long _ret;                                                            \
124 	register long _num  __asm__ ("rax") = (num);                          \
125 	register long _arg1 __asm__ ("rdi") = (long)(arg1);                   \
126 	register long _arg2 __asm__ ("rsi") = (long)(arg2);                   \
127 	register long _arg3 __asm__ ("rdx") = (long)(arg3);                   \
128 	register long _arg4 __asm__ ("r10") = (long)(arg4);                   \
129 	                                                                      \
130 	__asm__  volatile (                                                   \
131 		"syscall\n"                                                   \
132 		: "=a"(_ret)                                                  \
133 		: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4),             \
134 		  "0"(_num)                                                   \
135 		: "rcx", "r11", "memory", "cc"                                \
136 	);                                                                    \
137 	_ret;                                                                 \
138 })
139 
140 #define my_syscall5(num, arg1, arg2, arg3, arg4, arg5)                        \
141 ({                                                                            \
142 	long _ret;                                                            \
143 	register long _num  __asm__ ("rax") = (num);                          \
144 	register long _arg1 __asm__ ("rdi") = (long)(arg1);                   \
145 	register long _arg2 __asm__ ("rsi") = (long)(arg2);                   \
146 	register long _arg3 __asm__ ("rdx") = (long)(arg3);                   \
147 	register long _arg4 __asm__ ("r10") = (long)(arg4);                   \
148 	register long _arg5 __asm__ ("r8")  = (long)(arg5);                   \
149 	                                                                      \
150 	__asm__  volatile (                                                   \
151 		"syscall\n"                                                   \
152 		: "=a"(_ret)                                                  \
153 		: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
154 		  "0"(_num)                                                   \
155 		: "rcx", "r11", "memory", "cc"                                \
156 	);                                                                    \
157 	_ret;                                                                 \
158 })
159 
160 #define my_syscall6(num, arg1, arg2, arg3, arg4, arg5, arg6)                  \
161 ({                                                                            \
162 	long _ret;                                                            \
163 	register long _num  __asm__ ("rax") = (num);                          \
164 	register long _arg1 __asm__ ("rdi") = (long)(arg1);                   \
165 	register long _arg2 __asm__ ("rsi") = (long)(arg2);                   \
166 	register long _arg3 __asm__ ("rdx") = (long)(arg3);                   \
167 	register long _arg4 __asm__ ("r10") = (long)(arg4);                   \
168 	register long _arg5 __asm__ ("r8")  = (long)(arg5);                   \
169 	register long _arg6 __asm__ ("r9")  = (long)(arg6);                   \
170 	                                                                      \
171 	__asm__  volatile (                                                   \
172 		"syscall\n"                                                   \
173 		: "=a"(_ret)                                                  \
174 		: "r"(_arg1), "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
175 		  "r"(_arg6), "0"(_num)                                       \
176 		: "rcx", "r11", "memory", "cc"                                \
177 	);                                                                    \
178 	_ret;                                                                 \
179 })
180 
181 char **environ __attribute__((weak));
182 const unsigned long *_auxv __attribute__((weak));
183 
184 #define __ARCH_SUPPORTS_STACK_PROTECTOR
185 
186 /* startup code */
187 /*
188  * x86-64 System V ABI mandates:
189  * 1) %rsp must be 16-byte aligned right before the function call.
190  * 2) The deepest stack frame should be zero (the %rbp).
191  *
192  */
193 void __attribute__((weak,noreturn,optimize("omit-frame-pointer"))) _start(void)
194 {
195 	__asm__ volatile (
196 #ifdef NOLIBC_STACKPROTECTOR
197 		"call __stack_chk_init\n"   // initialize stack protector
198 #endif
199 		"pop %rdi\n"                // argc   (first arg, %rdi)
200 		"mov %rsp, %rsi\n"          // argv[] (second arg, %rsi)
201 		"lea 8(%rsi,%rdi,8),%rdx\n" // then a NULL then envp (third arg, %rdx)
202 		"mov %rdx, environ\n"       // save environ
203 		"xor %ebp, %ebp\n"          // zero the stack frame
204 		"mov %rdx, %rax\n"          // search for auxv (follows NULL after last env)
205 		"0:\n"
206 		"add $8, %rax\n"            // search for auxv using rax, it follows the
207 		"cmp -8(%rax), %rbp\n"      // ... NULL after last env (rbp is zero here)
208 		"jnz 0b\n"
209 		"mov %rax, _auxv\n"         // save it into _auxv
210 		"and $-16, %rsp\n"          // x86 ABI : esp must be 16-byte aligned before call
211 		"call main\n"               // main() returns the status code, we'll exit with it.
212 		"mov %eax, %edi\n"          // retrieve exit code (32 bit)
213 		"mov $60, %eax\n"           // NR_exit == 60
214 		"syscall\n"                 // really exit
215 		"hlt\n"                     // ensure it does not return
216 	);
217 	__builtin_unreachable();
218 }
219 
220 #endif // _NOLIBC_ARCH_X86_64_H
221