|SYSCALL(2)||System Calls Manual||SYSCALL(2)|
— indirect system call
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
Since different system calls have different return types, a
__syscall specifying the correct return
type should be declared locally. This is especially important for system
calls returning larger-than-int results.
__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, 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.
The predecessor of these functions, the former
indir() system call, first appeared in
Version 4 AT&T UNIX. The
syscall() function first appeared in
This would all be easier if the layout of structures with long long members matched how long long arguments were aligned on the stack for syscall arguments. They don't match for some ILP32 archs so explicit padding is necessary for consistent handling.
|May 30, 2016||OpenBSD-current|