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 syscall
() function call appeared in
4.0BSD.
BUGS
There is no way to simulate system calls that have multiple return values such as pipe(2).