🐧 NASM Assembly Linux Notes 🐧

🐧 Assembly with Linux (Notes, Syscalls, Protection Rings) 🐧

🐧 System Calls Linux (Syscalls) 🐧

❓ What is a System Call? ❓

When you run a program which calls open, fork, read, write (and many others) you are making a System Call.

System Calls are how a program enters the kernel to perform some task. Programs use System Calls to perform a variety of operations such as: creating processes, doing network and file IO, and much more.

Example: A user running a word processor in User Mode (Ring 3) presses “save”: a System Call is made into Kernel Mode (Ring 0), asking the Kernel to save the file.

📖 System Call Table (Syscall Table) 📖

#	Name	Registers
		eax	ebx	ecx	edx	esi	edi
0	sys_restart_syscall	0x00	-	-	-	-	-
1	sys_exit	0x01	int error_code	-	-	-	-
2	sys_fork	0x02	struct pt_regs *	-	-	-	-
3	sys_read	0x03	unsigned int fd	char __user *buf	size_t count	-	-
4	sys_write	0x04	unsigned int fd	const char __user *buf	size_t count	-	-
5	sys_open	0x05	const char __user *filename	int flags	int mode	-	-
6	sys_close	0x06	unsigned int fd	-	-	-	-
7	sys_waitpid	0x07	pid_t pid	int __user *stat_addr	int options	-	-
8	sys_creat	0x08	const char __user *pathname	int mode	-	-	-
9	sys_link	0x09	const char __user *oldname	const char __user *newname	-	-	-
10	sys_unlink	0x0a	const char __user *pathname	-	-	-	-
11	sys_execve	0x0b	char __user *	char __user *__user *	char __user *__user *	struct pt_regs *	-
12	sys_chdir	0x0c	const char __user *filename	-	-	-	-
13	sys_time	0x0d	time_t __user *tloc	-	-	-	-
14	sys_mknod	0x0e	const char __user *filename	int mode	unsigned dev	-	-
15	sys_chmod	0x0f	const char __user *filename	mode_t mode	-	-	-
16	sys_lchown16	0x10	const char __user *filename	old_uid_t user	old_gid_t group	-	-
17	not implemented	0x11	-	-	-	-	-
18	sys_stat	0x12	char __user *filename	struct __old_kernel_stat __user *statbuf	-	-	-
19	sys_lseek	0x13	unsigned int fd	off_t offset	unsigned int origin	-	-
20	sys_getpid	0x14	-	-	-	-	-
21	sys_mount	0x15	char __user *dev_name	char __user *dir_name	char __user *type	unsigned long flags	void __user *data
22	sys_oldumount	0x16	char __user *name	-	-	-	-
23	sys_setuid16	0x17	old_uid_t uid	-	-	-	-
24	sys_getuid16	0x18	-	-	-	-	-
25	sys_stime	0x19	time_t __user *tptr	-	-	-	-
26	sys_ptrace	0x1a	long request	long pid	long addr	long data	-
27	sys_alarm	0x1b	unsigned int seconds	-	-	-	-
28	sys_fstat	0x1c	unsigned int fd	struct __old_kernel_stat __user *statbuf	-	-	-
29	sys_pause	0x1d	-	-	-	-	-
30	sys_utime	0x1e	char __user *filename	struct utimbuf __user *times	-	-	-
31	not implemented	0x1f	-	-	-	-	-
32	not implemented	0x20	-	-	-	-	-
33	sys_access	0x21	const char __user *filename	int mode	-	-	-
34	sys_nice	0x22	int increment	-	-	-	-
35	not implemented	0x23	-	-	-	-	-
36	sys_sync	0x24	-	-	-	-	-
37	sys_kill	0x25	int pid	int sig	-	-	-
38	sys_rename	0x26	const char __user *oldname	const char __user *newname	-	-	-
39	sys_mkdir	0x27	const char __user *pathname	int mode	-	-	-
40	sys_rmdir	0x28	const char __user *pathname	-	-	-	-
41	sys_dup	0x29	unsigned int fildes	-	-	-	-
42	sys_pipe	0x2a	int __user *fildes	-	-	-	-
43	sys_times	0x2b	struct tms __user *tbuf	-	-	-	-
44	not implemented	0x2c	-	-	-	-	-
45	sys_brk	0x2d	unsigned long brk	-	-	-	-
46	sys_setgid16	0x2e	old_gid_t gid	-	-	-	-
47	sys_getgid16	0x2f	-	-	-	-	-
48	sys_signal	0x30	int sig	__sighandler_t handler	-	-	-
49	sys_geteuid16	0x31	-	-	-	-	-
50	sys_getegid16	0x32	-	-	-	-	-
51	sys_acct	0x33	const char __user *name	-	-	-	-
52	sys_umount	0x34	char __user *name	int flags	-	-	-
53	not implemented	0x35	-	-	-	-	-
54	sys_ioctl	0x36	unsigned int fd	unsigned int cmd	unsigned long arg	-	-
55	sys_fcntl	0x37	unsigned int fd	unsigned int cmd	unsigned long arg	-	-
56	not implemented	0x38	-	-	-	-	-
57	sys_setpgid	0x39	pid_t pid	pid_t pgid	-	-	-
58	not implemented	0x3a	-	-	-	-	-
59	sys_olduname	0x3b	struct oldold_utsname __user *	-	-	-	-
60	sys_umask	0x3c	int mask	-	-	-	-
61	sys_chroot	0x3d	const char __user *filename	-	-	-	-
62	sys_ustat	0x3e	unsigned dev	struct ustat __user *ubuf	-	-	-
63	sys_dup2	0x3f	unsigned int oldfd	unsigned int newfd	-	-	-
64	sys_getppid	0x40	-	-	-	-	-
65	sys_getpgrp	0x41	-	-	-	-	-
66	sys_setsid	0x42	-	-	-	-	-
67	sys_sigaction	0x43	int sig	const struct old_sigaction __user *act	struct old_sigaction __user *oact	-	-
68	sys_sgetmask	0x44	-	-	-	-	-
69	sys_ssetmask	0x45	int newmask	-	-	-	-
70	sys_setreuid16	0x46	old_uid_t ruid	old_uid_t euid	-	-	-
71	sys_setregid16	0x47	old_gid_t rgid	old_gid_t egid	-	-	-
72	sys_sigsuspend	0x48	int history0	int history1	old_sigset_t mask	-	-
73	sys_sigpending	0x49	old_sigset_t __user *set	-	-	-	-
74	sys_sethostname	0x4a	char __user *name	int len	-	-	-
75	sys_setrlimit	0x4b	unsigned int resource	struct rlimit __user *rlim	-	-	-
76	sys_old_getrlimit	0x4c	unsigned int resource	struct rlimit __user *rlim	-	-	-
77	sys_getrusage	0x4d	int who	struct rusage __user *ru	-	-	-
78	sys_gettimeofday	0x4e	struct timeval __user *tv	struct timezone __user *tz	-	-	-
79	sys_settimeofday	0x4f	struct timeval __user *tv	struct timezone __user *tz	-	-	-
80	sys_getgroups16	0x50	int gidsetsize	old_gid_t __user *grouplist	-	-	-
81	sys_setgroups16	0x51	int gidsetsize	old_gid_t __user *grouplist	-	-	-
82	sys_old_select	0x52	struct sel_arg_struct __user *arg	-	-	-	-
83	sys_symlink	0x53	const char __user *old	const char __user *new	-	-	-
84	sys_lstat	0x54	char __user *filename	struct __old_kernel_stat __user *statbuf	-	-	-
85	sys_readlink	0x55	const char __user *path	char __user *buf	int bufsiz	-	-
86	sys_uselib	0x56	const char __user *library	-	-	-	-
87	sys_swapon	0x57	const char __user *specialfile	int swap_flags	-	-	-
88	sys_reboot	0x58	int magic1	int magic2	unsigned int cmd	void __user *arg	-
89	sys_old_readdir	0x59	unsigned int	struct old_linux_dirent __user *	unsigned int	-	-
90	sys_old_mmap	0x5a	struct mmap_arg_struct __user *arg	-	-	-	-
91	sys_munmap	0x5b	unsigned long addr	size_t len	-	-	-
92	sys_truncate	0x5c	const char __user *path	long length	-	-	-
93	sys_ftruncate	0x5d	unsigned int fd	unsigned long length	-	-	-
94	sys_fchmod	0x5e	unsigned int fd	mode_t mode	-	-	-
95	sys_fchown16	0x5f	unsigned int fd	old_uid_t user	old_gid_t group	-	-
96	sys_getpriority	0x60	int which	int who	-	-	-
97	sys_setpriority	0x61	int which	int who	int niceval	-	-
98	not implemented	0x62	-	-	-	-	-
99	sys_statfs	0x63	const char __user * path	struct statfs __user *buf	-	-	-
100	sys_fstatfs	0x64	unsigned int fd	struct statfs __user *buf	-	-	-
101	sys_ioperm	0x65	unsigned long	unsigned long	int	-	-
102	sys_socketcall	0x66	int call	unsigned long __user *args	-	-	-
103	sys_syslog	0x67	int type	char __user *buf	int len	-	-
104	sys_setitimer	0x68	int which	struct itimerval __user *value	struct itimerval __user *ovalue	-	-
105	sys_getitimer	0x69	int which	struct itimerval __user *value	-	-	-
106	sys_newstat	0x6a	char __user *filename	struct stat __user *statbuf	-	-	-
107	sys_newlstat	0x6b	char __user *filename	struct stat __user *statbuf	-	-	-
108	sys_newfstat	0x6c	unsigned int fd	struct stat __user *statbuf	-	-	-
109	sys_uname	0x6d	struct old_utsname __user *	-	-	-	-
110	sys_iopl	0x6e	unsigned int	struct pt_regs *	-	-	-
111	sys_vhangup	0x6f	-	-	-	-	-
112	not implemented	0x70	-	-	-	-	-
113	sys_vm86old	0x71	struct vm86_struct __user *	struct pt_regs *	-	-	-
114	sys_wait4	0x72	pid_t pid	int __user *stat_addr	int options	struct rusage __user *ru	-
115	sys_swapoff	0x73	const char __user *specialfile	-	-	-	-
116	sys_sysinfo	0x74	struct sysinfo __user *info	-	-	-	-
117	sys_ipc	0x75	-	-	-	-	-
118	sys_fsync	0x76	unsigned int fd	-	-	-	-
119	sys_sigreturn	0x77	struct pt_regs *regs	-	-	-	-
120	sys_clone	0x78	unsigned long	unsigned long	unsigned long	unsigned long	struct pt_regs *
121	sys_setdomainname	0x79	char __user *name	int len	-	-	-
122	sys_newuname	0x7a	struct new_utsname __user *name	-	-	-	-
123	sys_modify_ldt	0x7b	int	void __user *	unsigned long	-	-
124	sys_adjtimex	0x7c	struct timex __user *txc_p	-	-	-	-
125	sys_mprotect	0x7d	unsigned long start	size_t len	unsigned long prot	-	-
126	sys_sigprocmask	0x7e	int how	old_sigset_t __user *set	old_sigset_t __user *oset	-	-
127	not implemented	0x7f	-	-	-	-	-
128	sys_init_module	0x80	void __user *umod	unsigned long len	const char __user *uargs	-	-
129	sys_delete_module	0x81	const char __user *name_user	unsigned int flags	-	-	-
130	not implemented	0x82	-	-	-	-	-
131	sys_quotactl	0x83	unsigned int cmd	const char __user *special	qid_t id	void __user *addr	-
132	sys_getpgid	0x84	pid_t pid	-	-	-	-
133	sys_fchdir	0x85	unsigned int fd	-	-	-	-
134	sys_bdflush	0x86	int func	long data	-	-	-
135	sys_sysfs	0x87	int option	unsigned long arg1	unsigned long arg2	-	-
136	sys_personality	0x88	unsigned int personality	-	-	-	-
137	not implemented	0x89	-	-	-	-	-
138	sys_setfsuid16	0x8a	old_uid_t uid	-	-	-	-
139	sys_setfsgid16	0x8b	old_gid_t gid	-	-	-	-
140	sys_llseek	0x8c	unsigned int fd	unsigned long offset_high	unsigned long offset_low	loff_t __user *result	unsigned int origin
141	sys_getdents	0x8d	unsigned int fd	struct linux_dirent __user *dirent	unsigned int count	-	-
142	sys_select	0x8e	int n	fd_set __user *inp	fd_set __user *outp	fd_set __user *exp	struct timeval __user *tvp
143	sys_flock	0x8f	unsigned int fd	unsigned int cmd	-	-	-
144	sys_msync	0x90	unsigned long start	size_t len	int flags	-	-
145	sys_readv	0x91	unsigned long fd	const struct iovec __user *vec	unsigned long vlen	-	-
146	sys_writev	0x92	unsigned long fd	const struct iovec __user *vec	unsigned long vlen	-	-
147	sys_getsid	0x93	pid_t pid	-	-	-	-
148	sys_fdatasync	0x94	unsigned int fd	-	-	-	-
149	sys_sysctl	0x95	struct __sysctl_args __user *args	-	-	-	-
150	sys_mlock	0x96	unsigned long start	size_t len	-	-	-
151	sys_munlock	0x97	unsigned long start	size_t len	-	-	-
152	sys_mlockall	0x98	int flags	-	-	-	-
153	sys_munlockall	0x99	-	-	-	-	-
154	sys_sched_setparam	0x9a	pid_t pid	struct sched_param __user *param	-	-	-
155	sys_sched_getparam	0x9b	pid_t pid	struct sched_param __user *param	-	-	-
156	sys_sched_setscheduler	0x9c	pid_t pid	int policy	struct sched_param __user *param	-	-
157	sys_sched_getscheduler	0x9d	pid_t pid	-	-	-	-
158	sys_sched_yield	0x9e	-	-	-	-	-
159	sys_sched_get_priority_max	0x9f	int policy	-	-	-	-
160	sys_sched_get_priority_min	0xa0	int policy	-	-	-	-
161	sys_sched_rr_get_interval	0xa1	pid_t pid	struct timespec __user *interval	-	-	-
162	sys_nanosleep	0xa2	struct timespec __user *rqtp	struct timespec __user *rmtp	-	-	-
163	sys_mremap	0xa3	unsigned long addr	unsigned long old_len	unsigned long new_len	unsigned long flags	unsigned long new_addr
164	sys_setresuid16	0xa4	old_uid_t ruid	old_uid_t euid	old_uid_t suid	-	-
165	sys_getresuid16	0xa5	old_uid_t __user *ruid	old_uid_t __user *euid	old_uid_t __user *suid	-	-
166	sys_vm86	0xa6	unsigned long	unsigned long	struct pt_regs *	-	-
167	not implemented	0xa7	-	-	-	-	-
168	sys_poll	0xa8	struct pollfd __user *ufds	unsigned int nfds	long timeout	-	-
169	sys_nfsservctl	0xa9	int cmd	struct nfsctl_arg __user *arg	void __user *res	-	-
170	sys_setresgid16	0xaa	old_gid_t rgid	old_gid_t egid	old_gid_t sgid	-	-
171	sys_getresgid16	0xab	old_gid_t __user *rgid	old_gid_t __user *egid	old_gid_t __user *sgid	-	-
172	sys_prctl	0xac	int option	unsigned long arg2	unsigned long arg3	unsigned long arg4	unsigned long arg5
173	sys_rt_sigreturn	0xad	struct pt_regs *	-	-	-	-
174	sys_rt_sigaction	0xae	int sig	const struct sigaction __user *act	struct sigaction __user *oact	size_t sigsetsize	-
175	sys_rt_sigprocmask	0xaf	int how	sigset_t __user *set	sigset_t __user *oset	size_t sigsetsize	-
176	sys_rt_sigpending	0xb0	sigset_t __user *set	size_t sigsetsize	-	-	-
177	sys_rt_sigtimedwait	0xb1	const sigset_t __user *uthese	siginfo_t __user *uinfo	const struct timespec __user *uts	size_t sigsetsize	-
178	sys_rt_sigqueueinfo	0xb2	int pid	int sig	siginfo_t __user *uinfo	-	-
179	sys_rt_sigsuspend	0xb3	sigset_t __user *unewset	size_t sigsetsize	-	-	-
180	sys_pread64	0xb4	unsigned int fd	char __user *buf	size_t count	loff_t pos	-
181	sys_pwrite64	0xb5	unsigned int fd	const char __user *buf	size_t count	loff_t pos	-
182	sys_chown16	0xb6	const char __user *filename	old_uid_t user	old_gid_t group	-	-
183	sys_getcwd	0xb7	char __user *buf	unsigned long size	-	-	-
184	sys_capget	0xb8	cap_user_header_t header	cap_user_data_t dataptr	-	-	-
185	sys_capset	0xb9	cap_user_header_t header	const cap_user_data_t data	-	-	-
186	sys_sigaltstack	0xba	const stack_t __user *	stack_t __user *	struct pt_regs *	-	-
187	sys_sendfile	0xbb	int out_fd	int in_fd	off_t __user *offset	size_t count	-
188	not implemented	0xbc	-	-	-	-	-
189	not implemented	0xbd	-	-	-	-	-
190	sys_vfork	0xbe	struct pt_regs *	-	-	-	-
191	sys_getrlimit	0xbf	unsigned int resource	struct rlimit __user *rlim	-	-	-
192	sys_mmap_pgoff	0xc0	-	-	-	-	-
193	sys_truncate64	0xc1	const char __user *path	loff_t length	-	-	-
194	sys_ftruncate64	0xc2	unsigned int fd	loff_t length	-	-	-
195	sys_stat64	0xc3	char __user *filename	struct stat64 __user *statbuf	-	-	-
196	sys_lstat64	0xc4	char __user *filename	struct stat64 __user *statbuf	-	-	-
197	sys_fstat64	0xc5	unsigned long fd	struct stat64 __user *statbuf	-	-	-
198	sys_lchown	0xc6	const char __user *filename	uid_t user	gid_t group	-	-
199	sys_getuid	0xc7	-	-	-	-	-
200	sys_getgid	0xc8	-	-	-	-	-
201	sys_geteuid	0xc9	-	-	-	-	-
202	sys_getegid	0xca	-	-	-	-	-
203	sys_setreuid	0xcb	uid_t ruid	uid_t euid	-	-	-
204	sys_setregid	0xcc	gid_t rgid	gid_t egid	-	-	-
205	sys_getgroups	0xcd	int gidsetsize	gid_t __user *grouplist	-	-	-
206	sys_setgroups	0xce	int gidsetsize	gid_t __user *grouplist	-	-	-
207	sys_fchown	0xcf	unsigned int fd	uid_t user	gid_t group	-	-
208	sys_setresuid	0xd0	uid_t ruid	uid_t euid	uid_t suid	-	-
209	sys_getresuid	0xd1	uid_t __user *ruid	uid_t __user *euid	uid_t __user *suid	-	-
210	sys_setresgid	0xd2	gid_t rgid	gid_t egid	gid_t sgid	-	-
211	sys_getresgid	0xd3	gid_t __user *rgid	gid_t __user *egid	gid_t __user *sgid	-	-
212	sys_chown	0xd4	const char __user *filename	uid_t user	gid_t group	-	-
213	sys_setuid	0xd5	uid_t uid	-	-	-	-
214	sys_setgid	0xd6	gid_t gid	-	-	-	-
215	sys_setfsuid	0xd7	uid_t uid	-	-	-	-
216	sys_setfsgid	0xd8	gid_t gid	-	-	-	-
217	sys_pivot_root	0xd9	const char __user *new_root	const char __user *put_old	-	-	-
218	sys_mincore	0xda	unsigned long start	size_t len	unsigned char __user * vec	-	-
219	sys_madvise	0xdb	unsigned long start	size_t len	int behavior	-	-
220	sys_getdents64	0xdc	unsigned int fd	struct linux_dirent64 __user *dirent	unsigned int count	-	-
221	sys_fcntl64	0xdd	unsigned int fd	unsigned int cmd	unsigned long arg	-	-
222	not implemented	0xde	-	-	-	-	-
223	not implemented	0xdf	-	-	-	-	-
224	sys_gettid	0xe0	-	-	-	-	-
225	sys_readahead	0xe1	int fd	loff_t offset	size_t count	-	-
226	sys_setxattr	0xe2	const char __user *path	const char __user *name	const void __user *value	size_t size	int flags
227	sys_lsetxattr	0xe3	const char __user *path	const char __user *name	const void __user *value	size_t size	int flags
228	sys_fsetxattr	0xe4	int fd	const char __user *name	const void __user *value	size_t size	int flags
229	sys_getxattr	0xe5	const char __user *path	const char __user *name	void __user *value	size_t size	-
230	sys_lgetxattr	0xe6	const char __user *path	const char __user *name	void __user *value	size_t size	-
231	sys_fgetxattr	0xe7	int fd	const char __user *name	void __user *value	size_t size	-
232	sys_listxattr	0xe8	const char __user *path	char __user *list	size_t size	-	-
233	sys_llistxattr	0xe9	const char __user *path	char __user *list	size_t size	-	-
234	sys_flistxattr	0xea	int fd	char __user *list	size_t size	-	-
235	sys_removexattr	0xeb	const char __user *path	const char __user *name	-	-	-
236	sys_lremovexattr	0xec	const char __user *path	const char __user *name	-	-	-
237	sys_fremovexattr	0xed	int fd	const char __user *name	-	-	-
238	sys_tkill	0xee	int pid	int sig	-	-	-
239	sys_sendfile64	0xef	int out_fd	int in_fd	loff_t __user *offset	size_t count	-
240	sys_futex	0xf0	-	-	-	-	-
241	sys_sched_setaffinity	0xf1	pid_t pid	unsigned int len	unsigned long __user *user_mask_ptr	-	-
242	sys_sched_getaffinity	0xf2	pid_t pid	unsigned int len	unsigned long __user *user_mask_ptr	-	-
243	sys_set_thread_area	0xf3	struct user_desc __user *	-	-	-	-
244	sys_get_thread_area	0xf4	struct user_desc __user *	-	-	-	-
245	sys_io_setup	0xf5	unsigned nr_reqs	aio_context_t __user *ctx	-	-	-
246	sys_io_destroy	0xf6	aio_context_t ctx	-	-	-	-
247	sys_io_getevents	0xf7	aio_context_t ctx_id	long min_nr	long nr	struct io_event __user *events	struct timespec __user *timeout
248	sys_io_submit	0xf8	aio_context_t	long	struct iocb __user * __user *	-	-
249	sys_io_cancel	0xf9	aio_context_t ctx_id	struct iocb __user *iocb	struct io_event __user *result	-	-
250	sys_fadvise64	0xfa	int fd	loff_t offset	size_t len	int advice	-
251	not implemented	0xfb	-	-	-	-	-
252	sys_exit_group	0xfc	int error_code	-	-	-	-
253	sys_lookup_dcookie	0xfd	u64 cookie64	char __user *buf	size_t len	-	-
254	sys_epoll_create	0xfe	int size	-	-	-	-
255	sys_epoll_ctl	0xff	int epfd	int op	int fd	struct epoll_event __user *event	-
256	sys_epoll_wait	0x100	int epfd	struct epoll_event __user *events	int maxevents	int timeout	-
257	sys_remap_file_pages	0x101	unsigned long start	unsigned long size	unsigned long prot	unsigned long pgoff	unsigned long flags
258	sys_set_tid_address	0x102	int __user *tidptr	-	-	-	-
259	sys_timer_create	0x103	clockid_t which_clock	struct sigevent __user *timer_event_spec	timer_t __user * created_timer_id	-	-
260	sys_timer_settime	0x104	timer_t timer_id	int flags	const struct itimerspec __user *new_setting	struct itimerspec __user *old_setting	-
261	sys_timer_gettime	0x105	timer_t timer_id	struct itimerspec __user *setting	-	-	-
262	sys_timer_getoverrun	0x106	timer_t timer_id	-	-	-	-
263	sys_timer_delete	0x107	timer_t timer_id	-	-	-	-
264	sys_clock_settime	0x108	clockid_t which_clock	const struct timespec __user *tp	-	-	-
265	sys_clock_gettime	0x109	clockid_t which_clock	struct timespec __user *tp	-	-	-
266	sys_clock_getres	0x10a	clockid_t which_clock	struct timespec __user *tp	-	-	-
267	sys_clock_nanosleep	0x10b	clockid_t which_clock	int flags	const struct timespec __user *rqtp	struct timespec __user *rmtp	-
268	sys_statfs64	0x10c	const char __user *path	size_t sz	struct statfs64 __user *buf	-	-
269	sys_fstatfs64	0x10d	unsigned int fd	size_t sz	struct statfs64 __user *buf	-	-
270	sys_tgkill	0x10e	int tgid	int pid	int sig	-	-
271	sys_utimes	0x10f	char __user *filename	struct timeval __user *utimes	-	-	-
272	sys_fadvise64_64	0x110	int fd	loff_t offset	loff_t len	int advice	-
273	not implemented	0x111	-	-	-	-	-
274	sys_mbind	0x112	-	-	-	-	-
275	sys_get_mempolicy	0x113	int __user *policy	unsigned long __user *nmask	unsigned long maxnode	unsigned long addr	unsigned long flags
276	sys_set_mempolicy	0x114	int mode	unsigned long __user *nmask	unsigned long maxnode	-	-
277	sys_mq_open	0x115	const char __user *name	int oflag	mode_t mode	struct mq_attr __user *attr	-
278	sys_mq_unlink	0x116	const char __user *name	-	-	-	-
279	sys_mq_timedsend	0x117	mqd_t mqdes	const char __user *msg_ptr	size_t msg_len	unsigned int msg_prio	const struct timespec __user *abs_timeout
280	sys_mq_timedreceive	0x118	mqd_t mqdes	char __user *msg_ptr	size_t msg_len	unsigned int __user *msg_prio	const struct timespec __user *abs_timeout
281	sys_mq_notify	0x119	mqd_t mqdes	const struct sigevent __user *notification	-	-	-
282	sys_mq_getsetattr	0x11a	mqd_t mqdes	const struct mq_attr __user *mqstat	struct mq_attr __user *omqstat	-	-
283	sys_kexec_load	0x11b	unsigned long entry	unsigned long nr_segments	struct kexec_segment __user *segments	unsigned long flags	-
284	sys_waitid	0x11c	int which	pid_t pid	struct siginfo __user *infop	int options	struct rusage __user *ru
285	not implemented	0x11d	-	-	-	-	-
286	sys_add_key	0x11e	const char __user *_type	const char __user *_description	const void __user *_payload	size_t plen	key_serial_t destringid
287	sys_request_key	0x11f	const char __user *_type	const char __user *_description	const char __user *_callout_info	key_serial_t destringid	-
288	sys_keyctl	0x120	int cmd	unsigned long arg2	unsigned long arg3	unsigned long arg4	unsigned long arg5
289	sys_ioprio_set	0x121	int which	int who	int ioprio	-	-
290	sys_ioprio_get	0x122	int which	int who	-	-	-
291	sys_inotify_init	0x123	-	-	-	-	-
292	sys_inotify_add_watch	0x124	int fd	const char __user *path	u32 mask	-	-
293	sys_inotify_rm_watch	0x125	int fd	__s32 wd	-	-	-
294	sys_migrate_pages	0x126	pid_t pid	unsigned long maxnode	const unsigned long __user *from	const unsigned long __user *to	-
295	sys_openat	0x127	int dfd	const char __user *filename	int flags	int mode	-
296	sys_mkdirat	0x128	int dfd	const char __user * pathname	int mode	-	-
297	sys_mknodat	0x129	int dfd	const char __user * filename	int mode	unsigned dev	-
298	sys_fchownat	0x12a	int dfd	const char __user *filename	uid_t user	gid_t group	int flag
299	sys_futimesat	0x12b	int dfd	char __user *filename	struct timeval __user *utimes	-	-
300	sys_fstatat64	0x12c	int dfd	char __user *filename	struct stat64 __user *statbuf	int flag	-
301	sys_unlinkat	0x12d	int dfd	const char __user * pathname	int flag	-	-
302	sys_renameat	0x12e	int olddfd	const char __user * oldname	int newdfd	const char __user * newname	-
303	sys_linkat	0x12f	int olddfd	const char __user *oldname	int newdfd	const char __user *newname	int flags
304	sys_symlinkat	0x130	const char __user * oldname	int newdfd	const char __user * newname	-	-
305	sys_readlinkat	0x131	int dfd	const char __user *path	char __user *buf	int bufsiz	-
306	sys_fchmodat	0x132	int dfd	const char __user * filename	mode_t mode	-	-
307	sys_faccessat	0x133	int dfd	const char __user *filename	int mode	-	-
308	sys_pselect6	0x134	-	-	-	-	-
309	sys_ppoll	0x135	struct pollfd __user *ufds	unsigned int nfds	struct timespec __user *tsp	const sigset_t __user *sigmask	size_t sigsetsize
310	sys_unshare	0x136	unsigned long unshare_flags	-	-	-	-
311	sys_set_robust_list	0x137	struct robust_list_head __user *head	size_t len	-	-	-
312	sys_get_robust_list	0x138	int pid	struct robust_list_head __user * __user *head_ptr	size_t __user *len_ptr	-	-
313	sys_splice	0x139	-	-	-	-	-
314	sys_sync_file_range	0x13a	int fd	loff_t offset	loff_t nbytes	unsigned int flags	-
315	sys_tee	0x13b	int fdin	int fdout	size_t len	unsigned int flags	-
316	sys_vmsplice	0x13c	int fd	const struct iovec __user *iov	unsigned long nr_segs	unsigned int flags	-
317	sys_move_pages	0x13d	-	-	-	-	-
318	sys_getcpu	0x13e	unsigned __user *cpu	unsigned __user *node	struct getcpu_cache __user *cache	-	-
319	sys_epoll_pwait	0x13f	-	-	-	-	-
320	sys_utimensat	0x140	int dfd	char __user *filename	struct timespec __user *utimes	int flags	-
321	sys_signalfd	0x141	int ufd	sigset_t __user *user_mask	size_t sizemask	-	-
322	sys_timerfd_create	0x142	int clockid	int flags	-	-	-
323	sys_eventfd	0x143	unsigned int count	-	-	-	-
324	sys_fallocate	0x144	int fd	int mode	loff_t offset	loff_t len	-
325	sys_timerfd_settime	0x145	int ufd	int flags	const struct itimerspec __user *utmr	struct itimerspec __user *otmr	-
326	sys_timerfd_gettime	0x146	int ufd	struct itimerspec __user *otmr	-	-	-
327	sys_signalfd4	0x147	int ufd	sigset_t __user *user_mask	size_t sizemask	int flags	-
328	sys_eventfd2	0x148	unsigned int count	int flags	-	-	-
329	sys_epoll_create1	0x149	int flags	-	-	-	-
330	sys_dup3	0x14a	unsigned int oldfd	unsigned int newfd	int flags	-	-
331	sys_pipe2	0x14b	int __user *fildes	int flags	-	-	-
332	sys_inotify_init1	0x14c	int flags	-	-	-	-
333	sys_preadv	0x14d	unsigned long fd	const struct iovec __user *vec	unsigned long vlen	unsigned long pos_l	unsigned long pos_h
334	sys_pwritev	0x14e	unsigned long fd	const struct iovec __user *vec	unsigned long vlen	unsigned long pos_l	unsigned long pos_h
335	sys_rt_tgsigqueueinfo	0x14f	pid_t tgid	pid_t pid	int sig	siginfo_t __user *uinfo	-
336	sys_perf_event_open	0x150	struct perf_event_attr __user *attr_uptr	pid_t pid	int cpu	int group_fd	unsigned long flags
337	sys_recvmmsg	0x151	int fd	struct mmsghdr __user *msg	unsigned int vlen	unsigned flags	struct timespec __user *timeout

🔧 Simple System Call Example calling SYS_WRITE (kernel opcode 4) 🔧

At Line 17: mov eax, 4 ; invoke SYS_WRITE (kernel opcode 4)

; Hello World Program
; Compile with: nasm -f elf helloworld.asm
; Link with (64 bit systems require elf_i386 option): ld -m elf_i386 helloworld.o -o helloworld
; Run with: ./helloworld
 
SECTION .data
msg     db      'Hello World!', 0Ah     ; assign msg variable with your message string
 
SECTION .text
global  _start
 
_start:
 
    mov     edx, 13     ; number of bytes to write - one for each letter plus 0Ah (line feed character)
    mov     ecx, msg    ; move the memory address of our message string into ecx
    mov     ebx, 1      ; write to the STDOUT file
    mov     eax, 4      ; invoke SYS_WRITE (kernel opcode 4)
    int     80h

🐧 Protection Rings / Privilege Levels 🐧

The x86-64 CPUs have a concept called Privilege Levels. (also often called Protection Rings)
Linux only uses Ring 0 and 3 for Kernel Mode (Ring 0) and User Mode (Ring 3). Thus, all user mode processes, running when the system is in any run level execute in Ring 3, until they make a System Call into kernel code, which transitions the cpu to Ring 0.

1. The Kernel runs at the most privileged level, called Ring 0. User programs run at Ring 3.
2. Ring 0 can execute any system instruction and is given full trust.
3. To enter Kernel Mode (Ring 0), you must perform a System Call. (Another Way to use Kernel Mode (Ring 0) is by writing Linux Kernel Modules in C.)
   Additional Info: In Windows you usually program a driver in C to use Kernel Mode (Ring 0) and like Linux, Windows only uses Ring 0 and 3 too.