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syscall, __syscall - indirect system call
Standard C Library (libc, -lc)
syscall(int number, ...);
__syscall(quad_t number, ...);
The syscall() function 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 The
__syscall() form should be used when one or more of the arguments 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 appeared in 4.0BSD.
There is no way to simulate system calls that have multiple return values
such as pipe(2).