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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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 2021-03-22 "Linux" "Linux Programmer's Manual"
40 _syscall \- invoking a system call without library support (OBSOLETE)
43 .B #include <linux/unistd.h>
50 The important thing to know about a system call is its prototype.
51 You need to know how many arguments, their types,
52 and the function return type.
53 There are seven macros that make the actual call into the system easier.
58 .RI _syscall X ( type , name , type1 , arg1 , type2 , arg2 ,...)
65 is 0\(en6, which are the number of arguments taken by the
69 is the return type of the system call
72 is the name of the system call
75 is the Nth argument's type
78 is the name of the Nth argument
80 These macros create a function called
82 with the arguments you
84 Once you include the _syscall() in your source file,
85 you call the system call by
88 .I /usr/include/linux/unistd.h
90 The use of these macros is Linux-specific, and deprecated.
92 Starting around kernel 2.6.18, the _syscall macros were removed
93 from header files supplied to user space.
97 (Some architectures, notably ia64, never provided the _syscall macros;
98 on those architectures,
100 was always required.)
102 The _syscall() macros
106 create one, especially for C++ users.
108 System calls are not required to return only positive or negative error
110 You need to read the source to be sure how it will return errors.
111 Usually, it is the negative of a standard error code,
114 The _syscall() macros will return the result
119 is nonnegative, but will return \-1 and set the variable
126 For the error codes, see
129 When defining a system call, the argument types
132 passed by-value or by-pointer (for aggregates like structs).
133 .\" The preferred way to invoke system calls that glibc does not know
136 .\" However, this mechanism can be used only if using a libc
137 .\" (such as glibc) that supports
140 .\" .I <sys/syscall.h>
141 .\" header file contains the required SYS_foo definition.
142 .\" Otherwise, the use of a _syscall macro is required.
149 #include <linux/unistd.h> /* for _syscallX macros/related stuff */
150 #include <linux/kernel.h> /* for struct sysinfo */
152 _syscall1(int, sysinfo, struct sysinfo *, info);
157 struct sysinfo s_info;
160 error = sysinfo(&s_info);
161 printf("code error = %d\en", error);
162 printf("Uptime = %lds\enLoad: 1 min %lu / 5 min %lu / 15 min %lu\en"
163 "RAM: total %lu / free %lu / shared %lu\en"
164 "Memory in buffers = %lu\enSwap: total %lu / free %lu\en"
165 "Number of processes = %d\en",
166 s_info.uptime, s_info.loads[0],
167 s_info.loads[1], s_info.loads[2],
168 s_info.totalram, s_info.freeram,
169 s_info.sharedram, s_info.bufferram,
170 s_info.totalswap, s_info.freeswap,
179 Load: 1 min 13376 / 5 min 5504 / 15 min 1152
180 RAM: total 15343616 / free 827392 / shared 8237056
181 Memory in buffers = 5066752
182 Swap: total 27881472 / free 24698880
183 Number of processes = 40