syscall, __syscall - indirect system call
Library Synopsis Description Return Values History Bugs
.In sys/syscall.h .In unistd.h int syscall "int number" ... off_t __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 .In sys/syscall.h . 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 BSD 4.0 .
There is no way to simulate system calls that have multiple return values such as pipe(2).