1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
|
.\" $OpenBSD: syscall.9,v 1.8 2010/09/19 13:17:25 jmc Exp $
.\"
.\" Copyright (c) 2003 Michael Shalayeff
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF MIND, USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd $Mdocdate: September 19 2010 $
.Dt SYSCALL 9
.Os
.Sh NAME
.Nm syscall
.Nd "system calls overview"
.Sh DESCRIPTION
System calls in the kernel are implemented through a set of
switch tables for each emulation type.
Each table is generated from the
.Dq master
file by
.Pa sys/kern/makesyscalls.sh
through the appropriate rules in the
.Pa Makefile .
.Pp
The
.Dq master
file is a text file consisting of a list of lines for each
system call.
Lines may be split by the means of back slashing the end of the line.
Each line is a set of fields separated by whitespace:
.Pp
.D1 Cd number type ...
.Pp
Where:
.Bl -tag -width number -compact
.It number
is the system call number;
.It type
is one of:
.Bl -tag -width COMPAT_XXX -compact
.It STD
always included;
.It OBSOL
obsolete, not included in the system;
.It UNIMPL
unimplemented, not included in the system;
.It NODEF
included, but don't define the syscall number;
.It NOARGS
included, but don't define the syscall args structure;
.It INDIR
included, but don't define the syscall args structure,
and allow it to be "really" varargs;
.It COMPAT_XX
a compatibility system call, only included if the corresponding
option is configured for the kernel (see
.Xr options 4 ) .
.El
.El
.Pp
The rest of the line for the STD, NODEF, NOARGS, and COMPAT_XX
types is:
.Pp
.D1 Cd { pseudo-proto } [alias]
.Pp
.Nm pseudo-proto
is a C-like prototype used to generate the system call argument list,
and alias is an optional name alias for the call.
The function in the prototype has to be defined somewhere in
the kernel sources as it will be used as an entry point for
the corresponding system call.
.Pp
For other types the rest of the line is a comment.
.Pp
To generate the header and code files from the
.Dq master
file a
.Xr make 1
command has to be run from the directory containing the
.Dq master
file.
.Ss Usage
Entry from the user space for the system call is machine dependent.
Typical code to invoke a system call from the machine dependent
sources might look like this:
.Bd -literal -offset indent
const struct sysent *callp;
register_t code, args[8], rval[2];
struct proc *p = curproc;
int code, nsys;
\&...
/* ``code'' is the system call number passed from the user space */
\&...
if (code < 0 || code >= nsys)
callp += p->p_emul->e_nosys; /* illegal */
else
callp += code;
/* copyin the arguments from the user space */
\&...
#ifdef SYSCALL_DEBUG
scdebug_call(p, code, args);
#endif
#ifdef KTRACE
if (KTRPOINT(p, KTR_SYSCALL))
ktrsyscall(p, code, argsize, args);
#endif
rval[0] = 0;
#if NSYSTRACE > 0
if (ISSET(p->p_flag, P_SYSTRACE))
error = systrace_redirect(code, p, args, rval);
else
#endif
error = (*callp->sy_call)(p, args, rval);
switch (error) {
case 0:
/* normal return */
\&...
break;
case ERESTART:
/*
* adjust PC to point before the system call
* in the user space in order for the return
* back there we reenter the kernel to repeat
* the same system call
*/
\&...
break;
case EJUSTRETURN:
/* just return */
break;
default:
/*
* an error returned:
* call an optional emulation errno mapping
* routine and return back to the user.
*/
if (p->p_emul->e_errno)
error = p->p_emul->e_errno[error];
\&...
break;
}
#ifdef SYSCALL_DEBUG
scdebug_ret(p, code, orig_error, rval);
#endif
userret(p, frame.tf_eip, sticks);
#ifdef KTRACE
if (KTRPOINT(p, KTR_SYSRET))
ktrsysret(p, code, orig_error, rval[0]);
#endif
.Ed
.Pp
The
.Dq SYSCALL_DEBUG
parts of the code are explained in the section
.Sx Debugging
later in the document.
For the
.Dq KTRACE
portions of the code refer to the
.Xr ktrace 9
document for further explanations.
.Dq NSYSTRACE
is a system call tracing facility and is explained in the
.Xr systrace 9
and
.Xr systrace 4
documents.
.Ss Debugging
For debugging purposes the line
.Pp
.D1 Cd option SYSCALL_DEBUG
.Pp
should be included in the kernel configuration file (see
.Xr options 4 ) .
This allows tracing for calls, returns, and arguments for both
implemented and non-implemented system calls.
A global integer variable
.Dq scdebug
contains a mask for the desired logging events:
.Pp
.Bl -tag -width SCDEBUG_SHOWARGS__ -compact
.It SCDEBUG_CALLS
(0x0001) show calls;
.It SCDEBUG_RETURNS
(0x0002) show returns;
.It SCDEBUG_ALL
(0x0004) show even syscalls that are implemented;
.It SCDEBUG_SHOWARGS
(0x0008) show arguments to calls.
.El
.Pp
Use
.Xr ddb 4
to set the
.Dq scdebug
to a value desired.
.Sh CODE REFERENCES
.Bl -tag -width sys/kern/syscalls.master -compact
.It Pa sys/kern/makesyscalls.sh
a
.Xr sh 1
script for generating C files out of the syscall master file;
.It Pa sys/{kern,compat/*}/syscalls.conf
a configuration file for the shell script above;
.It Pa sys/{kern,compat/*}/syscalls.master
master files describing names and numbers for the system calls;
.It Pa sys/{kern/,compat/*/*_}syscalls.c
system call names lists;
.It Pa sys/{kern/init,compat/*/*}_sysent.c
system call switch tables;
.It Pa sys/{sys/,compat/*/*_}syscallargs.h
system call argument lists;
.It Pa sys/{sys/,compat/*/*_}syscall.h
system call numbers.
.El
.Sh SEE ALSO
.Xr ktrace 2 ,
.Xr syscall 2 ,
.Xr systrace 4 ,
.Xr ktrace 9 ,
.Xr sysctl_int 9 ,
.Xr systrace 9
.Sh HISTORY
The
.Nm
section manual page appeared in
.Ox 3.4 .
|
