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SYSCALL(2)                    System Calls Manual                   SYSCALL(2)

     syscall, __syscall - indirect system call

     Standard C Library (libc, -lc)

     #include <sys/syscall.h>
     #include <unistd.h>

     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.  It should not be used in normal applications.

     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).

     Since architectures return 32 bit and 64 bit results in different
     registers, it may be impossible to portably convert the result of
     __syscall() to a 32bit value.  For instance sparc returns 32 bit values
     in %o0 and 64 bit values in %o0:%o1 (with %o0 containing the most
     significant part) so a 32 bit right shift of the result is needed to get
     a correct 32 bit result.

     Many architectures mask off the unwanted high bits of the syscall number,
     rather than returning an error.

     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>

NetBSD 9.99                     August 7, 2009                     NetBSD 9.99