2.9BSD/usr/man/man2/ucall.2

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.TH UCALL 2 
.UC
.SH NAME
ucall \- call a kernel subroutine from user mode
.SH SYNOPSIS
.B #include <sys/psw.h>
.br
.B #include <sys/types.h>
.PP
.B ucall(priority, function, arg0, arg1)
.br
.B int priority, arg0, arg1;
.br
.B caddr_t function;
.SH DESCRIPTION
.I Ucall
causes the processor priority to be set to
.I priority
and the specified
.I function
to be called with arguments
.IR arg0 " and " arg1 .
.I Priority
is one of PS_BR0, \&..., PS_BR7.
Processor priority is reset to PS_BR0 when
.I function
returns.
.PP
.I Ucall
is allowed only if the user is the superuser.
It is obviously extremely dangerous if misused.
.SH ERRORS
.I Ucall
will fail if:
.TP 20
[EPERM]
The process's effective user ID is not the super-user.
.SH SEE ALSO
autoconfig(8)
.SH BUGS
No address validations are attempted.
.SH ASSEMBLER
.nf
(local = 58., ucall = 9.)
.B sys local; 9f
\&. . .
.B \&.data
.B "9: sys ucall; priority; function; arg0; arg1"
.fi