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ucall(2) [bsd man page]

UCALL(2)							System Calls Manual							  UCALL(2)

ucall - call a kernel subroutine from user mode (2BSD) SYNOPSIS
#include <pdp/psl.h> #include <sys/types.h> ucall(priority, function, arg0, arg1) int priority, arg0, arg1; caddr_t function; DESCRIPTION
Ucall causes the processor priority to be set to priority and the specified kernel function to be called with arguments arg0 and arg1. Priority is one of PSL_BR0, ..., PSL_BR7. Processor priority is reset to PSL_BR0 when function returns. Ucall is allowed only if the user is the superuser. It is obviously extremely dangerous if misused. It's only current use is at system boot time to configure system devices by calling device drivers ... ERRORS
[EPERM] The caller is not the super-user. SEE ALSO
autoconfig(8) BUGS
No address validations are attempted. Ucall is unique to the PDP-11 and 2BSD; its use is discouraged. 3rd Berkeley Distribution January 22, 1987 UCALL(2)

Check Out this Related Man Page

PHYS(2) 							System Calls Manual							   PHYS(2)

phys - allow a process to access physical addresses (2BSD) SYNOPSIS
phys(segreg, size, physaddr) unsigned int segreg, size, physaddr; DESCRIPTION
The argument segreg specifies a process virtual (data-space) address range of 8K bytes starting at virtual address segregx8K bytes. This address range is mapped into physical address physaddrx64 bytes. Only the first sizex64 bytes of this mapping is addressable. If size is zero, any previous mapping of this virtual address range is nullified. For example, the call phys(7, 1, 0177775); will map virtual addresses 0160000-0160077 into physical addresses 017777500-017777577. In particular, virtual address 0160060 is the PDP-11 console located at physical address 017777560. This call may only be executed by the super-user. ERRORS
[EPERM] The process's effective user ID is not the super-user. [EINVAL] Segreg is less than 0 or greater than 7. [EINVAL] Size is less than 0 or greater than 128. SEE ALSO
PDP-11 segmentation hardware BUGS
On systems with ENABLE/34(tm) memory mapping boards, phys cannot be used to map in the I/O page. This system call is very dangerous. It is not considered a permanent part of the system. Phys is unique to the PDP-11 and 2BSD; its use is discouraged. 3rd Berkeley Distribution January 22, 1987 PHYS(2)
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