LINUX SYSTEM CALLS

The interface between an application program and the Operating System is through system calls.

What is a system call?

The operating system is responsible for

  • Process Management (starting, running, stopping processes)
  • File Management(creating, opening, closing, reading, writing, renaming files)
  • Memory Management (allocating, deallocating memory)
  • Other stuff (timing, scheduling, network management)

An application program makes a system call to get the operating system to perform a service for it, like reading from a file.

One nice thing about syscalls is that you don’t have to link with a C library, so your executables can be much smaller.

System Call Numbers

For the numbers of the syscalls, look in arch/i386/kernel/entry.S for sys_call_table. The syscall numbers are offsets into that table. Several spots in the table are occupied by the syscall sys_ni_syscall. This is a placeholder that either replaces an obsolete syscall or reserves a spot for future syscalls.

Incidentally, the system calls are called from the function system_call in the same file; in particular, they are called with the assembly instruction ‘call *SYMBOL_NAME(sys_call_table)(,%eax,4)’. The part ‘*SYMBOL_NAME(sys_call_table)’ just gets replaced by a symbol name in sys_call_table. SYMBOL_NAME is a macro defined in include/linux/linkage.h, and it just replaces itself with its argument.

steps-in-making-a-sytem-call

All Linux System Calls:-

%eax Name Source %ebx %ecx %edx %esx %edi
1 sys_exit kernel/exit.c int
2 sys_fork arch/i386/kernel/process.c struct pt_regs
3 sys_read fs/read_write.c unsigned int char * size_t
4 sys_write fs/read_write.c unsigned int const char * size_t
5 sys_open fs/open.c const char * int int
6 sys_close fs/open.c unsigned int
7 sys_waitpid kernel/exit.c pid_t unsigned int * int
8 sys_creat fs/open.c const char * int
9 sys_link fs/namei.c const char * const char *
10 sys_unlink fs/namei.c const char *
11 sys_execve arch/i386/kernel/process.c struct pt_regs
12 sys_chdir fs/open.c const char *
13 sys_time kernel/time.c int *
14 sys_mknod fs/namei.c const char * int dev_t
15 sys_chmod fs/open.c const char * mode_t
16 sys_lchown fs/open.c const char * uid_t gid_t
18 sys_stat fs/stat.c char * struct __old_kernel_stat *
19 sys_lseek fs/read_write.c unsigned int off_t unsigned int
20 sys_getpid kernel/sched.c
21 sys_mount fs/super.c char * char * char *
22 sys_oldumount fs/super.c char *
23 sys_setuid kernel/sys.c uid_t
24 sys_getuid kernel/sched.c
25 sys_stime kernel/time.c int *
26 sys_ptrace arch/i386/kernel/ptrace.c long long long long
27 sys_alarm kernel/sched.c unsigned int
28 sys_fstat fs/stat.c unsigned int struct __old_kernel_stat *
29 sys_pause arch/i386/kernel/sys_i386.c
30 sys_utime fs/open.c char * struct utimbuf *
33 sys_access fs/open.c const char * int
34 sys_nice kernel/sched.c int
36 sys_sync fs/buffer.c
37 sys_kill kernel/signal.c int int
38 sys_rename fs/namei.c const char * const char *
39 sys_mkdir fs/namei.c const char * int
40 sys_rmdir fs/namei.c const char *
41 sys_dup fs/fcntl.c unsigned int
42 sys_pipe arch/i386/kernel/sys_i386.c unsigned long *
43 sys_times kernel/sys.c struct tms *
45 sys_brk mm/mmap.c unsigned long
46 sys_setgid kernel/sys.c gid_t
47 sys_getgid kernel/sched.c
48 sys_signal kernel/signal.c int __sighandler_t
49 sys_geteuid kernel/sched.c
50 sys_getegid kernel/sched.c
51 sys_acct kernel/acct.c const char *
52 sys_umount fs/super.c char * int
54 sys_ioctl fs/ioctl.c unsigned int unsigned int unsigned long
55 sys_fcntl fs/fcntl.c unsigned int unsigned int unsigned long
57 sys_setpgid kernel/sys.c pid_t pid_t
59 sys_olduname arch/i386/kernel/sys_i386.c struct oldold_utsname *
60 sys_umask kernel/sys.c int
61 sys_chroot fs/open.c const char *
62 sys_ustat fs/super.c dev_t struct ustat *
63 sys_dup2 fs/fcntl.c unsigned int unsigned int
64 sys_getppid kernel/sched.c
65 sys_getpgrp kernel/sys.c
66 sys_setsid kernel/sys.c
67 sys_sigaction arch/i386/kernel/signal.c int const struct old_sigaction * struct old_sigaction *
68 sys_sgetmask kernel/signal.c
69 sys_ssetmask kernel/signal.c int
70 sys_setreuid kernel/sys.c uid_t uid_t
71 sys_setregid kernel/sys.c gid_t gid_t
72 sys_sigsuspend arch/i386/kernel/signal.c int int old_sigset_t
73 sys_sigpending kernel/signal.c old_sigset_t *
74 sys_sethostname kernel/sys.c char * int
75 sys_setrlimit kernel/sys.c unsigned int struct rlimit *
76 sys_getrlimit kernel/sys.c unsigned int struct rlimit *
77 sys_getrusage kernel/sys.c int struct rusage *
78 sys_gettimeofday kernel/time.c struct timeval * struct timezone *
79 sys_settimeofday kernel/time.c struct timeval * struct timezone *
80 sys_getgroups kernel/sys.c int gid_t *
81 sys_setgroups kernel/sys.c int gid_t *
82 old_select arch/i386/kernel/sys_i386.c struct sel_arg_struct *
83 sys_symlink fs/namei.c const char * const char *
84 sys_lstat fs/stat.c char * struct __old_kernel_stat *
85 sys_readlink fs/stat.c const char * char * int
86 sys_uselib fs/exec.c const char *
87 sys_swapon mm/swapfile.c const char * int
88 sys_reboot kernel/sys.c int int int void *
89 old_readdir fs/readdir.c unsigned int void * unsigned int
90 old_mmap arch/i386/kernel/sys_i386.c struct mmap_arg_struct *
91 sys_munmap mm/mmap.c unsigned long size_t
92 sys_truncate fs/open.c const char * unsigned long
93 sys_ftruncate fs/open.c unsigned int unsigned long
94 sys_fchmod fs/open.c unsigned int mode_t
95 sys_fchown fs/open.c unsigned int uid_t gid_t
96 sys_getpriority kernel/sys.c int int
97 sys_setpriority kernel/sys.c int int int
99 sys_statfs fs/open.c const char * struct statfs *
100 sys_fstatfs fs/open.c unsigned int struct statfs *
101 sys_ioperm arch/i386/kernel/ioport.c unsigned long unsigned long int
102 sys_socketcall net/socket.c int unsigned long *
103 sys_syslog kernel/printk.c int char * int
104 sys_setitimer kernel/itimer.c int struct itimerval * struct itimerval *
105 sys_getitimer kernel/itimer.c int struct itimerval *
106 sys_newstat fs/stat.c char * struct stat *
107 sys_newlstat fs/stat.c char * struct stat *
108 sys_newfstat fs/stat.c unsigned int struct stat *
109 sys_uname arch/i386/kernel/sys_i386.c struct old_utsname *
110 sys_iopl arch/i386/kernel/ioport.c unsigned long
111 sys_vhangup fs/open.c
112 sys_idle arch/i386/kernel/process.c
113 sys_vm86old arch/i386/kernel/vm86.c unsigned long struct vm86plus_struct *
114 sys_wait4 kernel/exit.c pid_t unsigned long * int options struct rusage *
115 sys_swapoff mm/swapfile.c const char *
116 sys_sysinfo kernel/info.c struct sysinfo *
117 sys_ipc arch/i386/kernel/sys_i386.c uint int int int void *
118 sys_fsync fs/buffer.c unsigned int
119 sys_sigreturn arch/i386/kernel/signal.c unsigned long
120 sys_clone arch/i386/kernel/process.c struct pt_regs
121 sys_setdomainname kernel/sys.c char * int
122 sys_newuname kernel/sys.c struct new_utsname *
123 sys_modify_ldt arch/i386/kernel/ldt.c int void * unsigned long
124 sys_adjtimex kernel/time.c struct timex *
125 sys_mprotect mm/mprotect.c unsigned long size_t unsigned long
126 sys_sigprocmask kernel/signal.c int old_sigset_t * old_sigset_t *
127 sys_create_module kernel/module.c const char * size_t
128 sys_init_module kernel/module.c const char * struct module *
129 sys_delete_module kernel/module.c const char *
130 sys_get_kernel_syms kernel/module.c struct kernel_sym *
131 sys_quotactl fs/dquot.c int const char * int caddr_t
132 sys_getpgid kernel/sys.c pid_t
133 sys_fchdir fs/open.c unsigned int
134 sys_bdflush fs/buffer.c int long
135 sys_sysfs fs/super.c int unsigned long unsigned long
136 sys_personality kernel/exec_domain.c unsigned long
138 sys_setfsuid kernel/sys.c uid_t
139 sys_setfsgid kernel/sys.c gid_t
140 sys_llseek fs/read_write.c unsigned int unsigned long unsigned long loff_t * unsigned int
141 sys_getdents fs/readdir.c unsigned int void * unsigned int
142 sys_select fs/select.c int fd_set * fd_set * fd_set * struct timeval *
143 sys_flock fs/locks.c unsigned int unsigned int
144 sys_msync mm/filemap.c unsigned long size_t int
145 sys_readv fs/read_write.c unsigned long const struct iovec * unsigned long
146 sys_writev fs/read_write.c unsigned long const struct iovec * unsigned long
147 sys_getsid kernel/sys.c pid_t
148 sys_fdatasync fs/buffer.c unsigned int
149 sys_sysctl kernel/sysctl.c struct __sysctl_args *
150 sys_mlock mm/mlock.c unsigned long size_t
151 sys_munlock mm/mlock.c unsigned long size_t
152 sys_mlockall mm/mlock.c int
153 sys_munlockall mm/mlock.c
154 sys_sched_setparam kernel/sched.c pid_t struct sched_param *
155 sys_sched_getparam kernel/sched.c pid_t struct sched_param *
156 sys_sched_setscheduler kernel/sched.c pid_t int struct sched_param *
157 sys_sched_getscheduler kernel/sched.c pid_t
158 sys_sched_yield kernel/sched.c
159 sys_sched_get_priority_max kernel/sched.c int
160 sys_sched_get_priority_min kernel/sched.c int
161 sys_sched_rr_get_interval kernel/sched.c pid_t struct timespec *
162 sys_nanosleep kernel/sched.c struct timespec * struct timespec *
163 sys_mremap mm/mremap.c unsigned long unsigned long unsigned long unsigned long
164 sys_setresuid kernel/sys.c uid_t uid_t uid_t
165 sys_getresuid kernel/sys.c uid_t * uid_t * uid_t *
166 sys_vm86 arch/i386/kernel/vm86.c struct vm86_struct *
167 sys_query_module kernel/module.c const char * int char * size_t size_t *
168 sys_poll fs/select.c struct pollfd * unsigned int long
169 sys_nfsservctl fs/filesystems.c int void * void *
170 sys_setresgid kernel/sys.c gid_t gid_t gid_t
171 sys_getresgid kernel/sys.c gid_t * gid_t * gid_t *
172 sys_prctl kernel/sys.c int unsigned long unsigned long unsigned long unsigned long
173 sys_rt_sigreturn arch/i386/kernel/signal.c unsigned long
174 sys_rt_sigaction kernel/signal.c int const struct sigaction * struct sigaction * size_t
175 sys_rt_sigprocmask kernel/signal.c int sigset_t * sigset_t * size_t
176 sys_rt_sigpending kernel/signal.c sigset_t * size_t
177 sys_rt_sigtimedwait kernel/signal.c const sigset_t * siginfo_t * const struct timespec * size_t
178 sys_rt_sigqueueinfo kernel/signal.c int int siginfo_t *
179 sys_rt_sigsuspend arch/i386/kernel/signal.c sigset_t * size_t
180 sys_pread fs/read_write.c unsigned int char * size_t loff_t
181 sys_pwrite fs/read_write.c unsigned int const char * size_t loff_t
182 sys_chown fs/open.c const char * uid_t gid_t
183 sys_getcwd fs/dcache.c char * unsigned long
184 sys_capget kernel/capability.c cap_user_header_t cap_user_data_t
185 sys_capset kernel/capability.c cap_user_header_t const cap_user_data_t
186 sys_sigaltstack arch/i386/kernel/signal.c const stack_t * stack_t *
187 sys_sendfile mm/filemap.c int int off_t * size_t
190 sys_vfork arch/i386/kernel/process.c struct pt_regs

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