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mac OS 上 x86 使用syscall，32位 int 0x80。
中断号定义在#import <sys/syscall.h>
调用分几种
syscall_sw.h的定义
#define SYSCALL_CLASS_NONE 0 /* Invalid */
#define SYSCALL_CLASS_MACH 1 /* Mach */
#define SYSCALL_CLASS_UNIX 2 /* Unix/BSD */
#define SYSCALL_CLASS_MDEP 3 /* Machine-dependent */
#define SYSCALL_CLASS_DIAG 4 /* Diagnostics */
#define SYSCALL_CLASS_IPC 5 /* Mach IPC */
/* Macros to simpllfy constructing syscall numbers. */
#define SYSCALL_CONSTRUCT_MACH(syscall_number) \
((SYSCALL_CLASS_MACH << SYSCALL_CLASS_SHIFT) | \
(SYSCALL_NUMBER_MASK & (syscall_number)))
#define SYSCALL_CONSTRUCT_UNIX(syscall_number) \
((SYSCALL_CLASS_UNIX << SYSCALL_CLASS_SHIFT) | \
(SYSCALL_NUMBER_MASK & (syscall_number)))
#define SYSCALL_CONSTRUCT_MDEP(syscall_number) \
((SYSCALL_CLASS_MDEP << SYSCALL_CLASS_SHIFT) | \
(SYSCALL_NUMBER_MASK & (syscall_number)))
#define SYSCALL_CONSTRUCT_DIAG(syscall_number) \
((SYSCALL_CLASS_DIAG << SYSCALL_CLASS_SHIFT) | \
(SYSCALL_NUMBER_MASK & (syscall_number)))
对于Mach调用，调用的中断号是：中断号+ (1<<24)
对于Unix调用，调用的中断号是：中断号+ (2<<24)
exit的中断号是1，所以调用时的rax参数是0x2000001。
rdi是调用exit的参数
libsystem_kernel.dylib`mach_msg_trap:
0x7fff6bf982b0 <+0>: movq %rcx, %r10
0x7fff6bf982b3 <+3>: movl $0x100001f, %eax ; imm = 0x100001F
0x7fff6bf982b8 <+8>: syscall
-> 0x7fff6bf982ba <+10>: retq
0x7fff6bf982bb <+11>: nop
rax = 0x000000000100001f
rbx = 0x0000000000002303
rcx = 0x0000000000000c00
rdx = 0x0000000000000000
rdi = 0x00007ffee2a6dee0
rsi = 0x0000000007000806
rbp = 0x00007ffee2a6dd50
rsp = 0x00007ffee2a6dcf8
r8 = 0x0000000000002303
r9 = 0x00000000ffffffff
r10 = 0x0000000000000c00
r11 = 0x0000000000000346
r12 = 0x0000000007000806
r13 = 0x0000000000000c00
r14 = 0x00007ffee2a6dee0
r15 = 0x00000000ffffffff
rip = 0x00007fff6bf982b8 libsystem_kernel.dylib`mach_msg_trap + 8
rflags = 0x0000000000000246
cs = 0x000000000000002b
fs = 0x0000000000000000
gs = 0x0000000000000000
arm64上，x16保存调用号，svc #0x80表示系统调用，x0表示调用的参数
libsystem_kernel.dylib`mach_msg_trap:
0x1b967855c <+0>: mov x16, #-0x1f
0x1b9678560 <+4>: svc #0x80
-> 0x1b9678564 <+8>: ret
x0 = 0x000000016f5e7f70
x1 = 0x0000000000000003
x2 = 0x0000000000000028
x3 = 0x0000000000000140
x4 = 0x0000000000000603
x5 = 0x0000000000000000
x6 = 0x0000000000000000
x7 = 0x0000000000000000
x8 = 0x00000000fffffbbf
x9 = 0x0000000000000044
x10 = 0x000000016f5ebe53
x11 = 0x00000001f28ca6dd "ASL_DISABLE"
x12 = 0x0000000000000053
x13 = 0x0000000000000041
x14 = 0x0000000000000005
x15 = 0x000000000000000c
x16 = 0xffffffffffffffe1
x17 = 0x6ae100016f5e8450
x18 = 0x0000000000000000
x19 = 0x0000000000000000
x20 = 0x0000000000000000
x21 = 0x0000000000000603
x22 = 0x0000000000000140
x23 = 0x000000016f5e7f70
x24 = 0x0000000000000003
x25 = 0x0000000000000028
x26 = 0x0000000000000003
x27 = 0x00000002052ac000 __pthread_head
x28 = 0x0000000100ad8580 dyld`_main_thread
fp = 0x000000016f5e7f60
lr = 0x00000001b9678bfc libsystem_kernel.dylib`mach_msg + 76
sp = 0x000000016f5e7f10
pc = 0x00000001b9678560 libsystem_kernel.dylib`mach_msg_trap + 4
cpsr = 0x80000000
https://github.com/apple/darwin-xnu/blob/main/osfmk/mach/syscall_sw.h
https://opensource.apple.com/source/xnu/xnu-1504.3.12/bsd/kern/syscalls.master
https://www.bilibili.com/read/cv9033324
https://opensource.apple.com/source/xnu/xnu-4570.1.46/osfmk/mach/i386/syscall_sw.h.auto.html
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