NAME
syscall, __syscall
— indirect system
call
SYNOPSIS
#include
<sys/syscall.h>
#include <unistd.h>
int
syscall(int
number, ...);
__syscall(quad_t
number, ...);
DESCRIPTION
syscall()
performs the system call whose assembly language interface has the specified
number with the specified arguments. Symbolic
constants for system calls can be found in the header file
<sys/syscall.h>.
Since different system calls have different return types, a
prototype of __syscall specifying the correct return
type should be declared locally. This is especially important for system
calls returning larger-than-int results.
The __syscall form should be used when one
or more of the parameters is a 64-bit argument to ensure that argument
alignment is correct. This system call is useful for testing new system
calls that do not have entries in the C library.
RETURN VALUES
The return values are defined by the system call being invoked. In general, for system calls returning int, a 0 return value indicates success. A -1 return value indicates an error, and an error code is stored in errno.
HISTORY
The predecessor of these functions, the former
indir() system call, first appeared in
Version 4 AT&T UNIX. The
syscall() function first appeared in
3BSD.
BUGS
There is no way to simulate system calls that have multiple return values such as pipe(2).