syscall, __syscall - indirect system call
Standard C Library (libc, -lc)
syscall(int number, ...);
__syscall(quad_t number, ...);
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>. 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.
The return values are defined by the system call being invoked. In general,
a 0 return value indicates success. A -1 return value indicates an
error, and an error code is stored in errno.
The syscall() function call appeared in 4.0BSD.
There is no way to simulate system calls that have multiple return values
such as pipe(2).
Due to ABI implementation differences in passing struct or union type
arguments to system calls between different processors, all system calls
pass instead pointers to such structs or unions, even when the documentation
of the system call mentions otherwise. The conversion between passing
structs and unions is handled normally via userland stubs. The correct
arguments for the kernel entry points for each system call can be
found in the header file <sys/syscallargs.h>
BSD June 16, 1993 BSD
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