-.\"
.\" Copyright (c) 1993 Michael Haardt (michael@moria.de),
.\" Fri Apr 2 11:32:09 MET DST 1993
.\"
+.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public
-.\" License along with this manual; if not, write to the Free
-.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
-.\" USA.
+.\" License along with this manual; if not, see
+.\" <http://www.gnu.org/licenses/>.
+.\" %%%LICENSE_END
.\"
.\" Tue Jul 6 12:42:46 MDT 1993 <dminer@nyx.cs.du.edu>
.\" Added "Calling Directly" and supporting paragraphs
.\" 2007-10-23 mtk: created as a new page, by taking the content
.\" specific to the _syscall() macros from intro(2).
.\"
-.TH _SYSCALL 2 2007-12-19 "Linux" "Linux Programmer's Manual"
+.TH _SYSCALL 2 2017-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
_syscall \- invoking a system call without library support (OBSOLETE)
-.SH "SYNOPSIS"
+.SH SYNOPSIS
.B #include <linux/unistd.h>
-
+.PP
A _syscall macro
-
+.PP
desired system call
.SH DESCRIPTION
The important thing to know about a system call is its prototype.
You need to know how many arguments, their types,
and the function return type.
-There are six macros that make the actual call into the system easier.
+There are seven macros that make the actual call into the system easier.
They have the form:
-.sp
-.RS
+.PP
+.in +4n
+.EX
.RI _syscall X ( type , name , type1 , arg1 , type2 , arg2 ,...)
-.RE
+.EE
+.in
.PP
where
.IP
-\fIX\fP is 0\(en6, which are the number of arguments taken by the
+.I X
+is 0\(en6, which are the number of arguments taken by the
system call
.IP
-\fItype\fP is the return type of the system call
+.I type
+is the return type of the system call
.IP
-\fIname\fP is the name of the system call
+.I name
+is the name of the system call
.IP
-\fItypeN\fP is the Nth argument's type
+.I typeN
+is the Nth argument's type
.IP
-\fIargN\fP is the name of the Nth argument
+.I argN
+is the name of the Nth argument
.PP
-These macros create a function called \fIname\fP with the arguments you
+These macros create a function called
+.I name
+with the arguments you
specify.
Once you include the _syscall() in your source file,
-you call the system call by \fIname\fP.
+you call the system call by
+.IR name .
.SH FILES
.I /usr/include/linux/unistd.h
-.SH "CONFORMING TO"
+.SH CONFORMING TO
The use of these macros is Linux-specific, and deprecated.
.SH NOTES
Starting around kernel 2.6.18, the _syscall macros were removed
on those architectures,
.BR syscall (2)
was always required.)
-
-The _syscall() macros \fI do not\fP produce a prototype.
+.PP
+The _syscall() macros
+.I "do not"
+produce a prototype.
You may have to
create one, especially for C++ users.
-.sp
+.PP
System calls are not required to return only positive or negative error
codes.
You need to read the source to be sure how it will return errors.
Usually, it is the negative of a standard error code,
-for example, \-\fBEPERM\fP.
-The _syscall() macros will return the result \fIr\fP of the system call
-when \fIr\fP is non-negative, but will return \-1 and set the variable
+for example,
+.RI \- EPERM .
+The _syscall() macros will return the result
+.I r
+of the system call
+when
+.I r
+is nonnegative, but will return \-1 and set the variable
.I errno
-to \-\fIr\fP when \fIr\fP is negative.
+to
+.RI \- r
+when
+.I r
+is negative.
For the error codes, see
.BR errno (3).
-
-When defining a system call, the argument types \fImust\fP be
+.PP
+When defining a system call, the argument types
+.I must
+be
passed by-value or by-pointer (for aggregates like structs).
.\" The preferred way to invoke system calls that glibc does not know
.\" about yet is via
.\" .BR syscall (2).
-.\" However, this mechanism can only be used if using a libc
+.\" However, this mechanism can be used only if using a libc
.\" (such as glibc) that supports
.\" .BR syscall (2),
.\" and if the
.\" Otherwise, the use of a _syscall macro is required.
.\"
.SH EXAMPLE
-.sp
-.nf
+.EX
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
_syscall1(int, sysinfo, struct sysinfo *, info);
-/* Note: if you copy directly from the nroff source, remember to
-REMOVE the extra backslashes in the printf statement. */
-
int
main(void)
{
s_info.procs);
exit(EXIT_SUCCESS);
}
-.fi
-.SS "Sample Output"
-.nf
+.EE
+.SS Sample output
+.EX
code error = 0
uptime = 502034s
Load: 1 min 13376 / 5 min 5504 / 15 min 1152
Memory in buffers = 5066752
Swap: total 27881472 / free 24698880
Number of processes = 40
-.fi
-.SH "SEE ALSO"
+.EE
+.SH SEE ALSO
.BR intro (2),
.BR syscall (2),
.BR errno (3)
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