__syscall(2) indirect system call

Other Alias



Lb libc


In sys/syscall.h In unistd.h Ft int Fn syscall int number ... Ft off_t Fn __syscall quad_t number ...


The Fn syscall function performs the system call whose assembly language interface has the specified Fa number with the specified arguments. Symbolic constants for system calls can be found in the header file In sys/syscall.h . The Fn __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 Fn syscall function appeared in BSD 4.0


There is no way to simulate system calls that have multiple return values such as pipe(2).