1 .\" Copyright (c) 1993 Michael Haardt (michael@moria.de),
2 .\" Fri Apr 2 11:32:09 MET DST 1993
4 .\" %%%LICENSE_START(GPLv2+_DOC_FULL)
5 .\" This is free documentation; you can redistribute it and/or
6 .\" modify it under the terms of the GNU General Public License as
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13 .\" intermediate and printed output.
15 .\" This manual is distributed in the hope that it will be useful,
16 .\" but WITHOUT ANY WARRANTY; without even the implied warranty of
17 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 .\" GNU General Public License for more details.
20 .\" You should have received a copy of the GNU General Public
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22 .\" <http://www.gnu.org/licenses/>.
25 .\" Tue Jul 6 12:42:46 MDT 1993 <dminer@nyx.cs.du.edu>
26 .\" Added "Calling Directly" and supporting paragraphs
28 .\" Modified Sat Jul 24 15:19:12 1993 by Rik Faith <faith@cs.unc.edu>
30 .\" Modified 21 Aug 1994 by Michael Chastain <mec@shell.portal.com>:
31 .\" Added explanation of arg stacking when 6 or more args.
33 .\" Modified 10 June 1995 by Andries Brouwer <aeb@cwi.nl>
35 .\" 2007-10-23 mtk: created as a new page, by taking the content
36 .\" specific to the _syscall() macros from intro(2).
38 .TH _SYSCALL 2 2017-09-15 "Linux" "Linux Programmer's Manual"
40 _syscall \- invoking a system call without library support (OBSOLETE)
42 .B #include <linux/unistd.h>
48 The important thing to know about a system call is its prototype.
49 You need to know how many arguments, their types,
50 and the function return type.
51 There are seven macros that make the actual call into the system easier.
56 .RI _syscall X ( type , name , type1 , arg1 , type2 , arg2 ,...)
63 is 0\(en6, which are the number of arguments taken by the
67 is the return type of the system call
70 is the name of the system call
73 is the Nth argument's type
76 is the name of the Nth argument
78 These macros create a function called
80 with the arguments you
82 Once you include the _syscall() in your source file,
83 you call the system call by
86 .I /usr/include/linux/unistd.h
88 The use of these macros is Linux-specific, and deprecated.
90 Starting around kernel 2.6.18, the _syscall macros were removed
91 from header files supplied to user space.
95 (Some architectures, notably ia64, never provided the _syscall macros;
96 on those architectures,
100 The _syscall() macros
104 create one, especially for C++ users.
106 System calls are not required to return only positive or negative error
108 You need to read the source to be sure how it will return errors.
109 Usually, it is the negative of a standard error code,
112 The _syscall() macros will return the result
117 is nonnegative, but will return \-1 and set the variable
124 For the error codes, see
127 When defining a system call, the argument types
130 passed by-value or by-pointer (for aggregates like structs).
131 .\" The preferred way to invoke system calls that glibc does not know
134 .\" However, this mechanism can be used only if using a libc
135 .\" (such as glibc) that supports
138 .\" .I <sys/syscall.h>
139 .\" header file contains the required SYS_foo definition.
140 .\" Otherwise, the use of a _syscall macro is required.
147 #include <linux/unistd.h> /* for _syscallX macros/related stuff */
148 #include <linux/kernel.h> /* for struct sysinfo */
150 _syscall1(int, sysinfo, struct sysinfo *, info);
155 struct sysinfo s_info;
158 error = sysinfo(&s_info);
159 printf("code error = %d\\n", error);
160 printf("Uptime = %lds\\nLoad: 1 min %lu / 5 min %lu / 15 min %lu\\n"
161 "RAM: total %lu / free %lu / shared %lu\\n"
162 "Memory in buffers = %lu\\nSwap: total %lu / free %lu\\n"
163 "Number of processes = %d\\n",
164 s_info.uptime, s_info.loads[0],
165 s_info.loads[1], s_info.loads[2],
166 s_info.totalram, s_info.freeram,
167 s_info.sharedram, s_info.bufferram,
168 s_info.totalswap, s_info.freeswap,
177 Load: 1 min 13376 / 5 min 5504 / 15 min 1152
178 RAM: total 15343616 / free 827392 / shared 8237056
179 Memory in buffers = 5066752
180 Swap: total 27881472 / free 24698880
181 Number of processes = 40