freebsd-dev/usr.bin/uac/uac.1

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.Dd January 18, 2000
.Dt UAC 1
.Os
.Sh NAME
.Nm uac
.Nd Unaligned Access Message Control
.Sh SYNOPSIS
.Nm
.Op Fl fprs
.Sh DESCRIPTION
The
.Nm
utility sets the per-process handling of
.Dq Unaligned Access
events.
Unlike many other CPU's the DEC Alpha processor cannot access unaligned data.
To work around this, the Alpha has the ability to fix the UA fault
rather than send the faulting process a
.Dv SIGBUS
signal.
However, doing so does slow down the
execution of the faulting process.
At bootup, the DEC Alpha CPU defaults to printing
.Bd -ragged
.Em pid
.Ar nnn Pq Ar <progname> :
unaligned access:
.Em va Ns = Ns Ar 0xADDR
.Em pc Ns = Ns Ar 0xADDR
.Em ra Ns = Ns Ar 0xADDR
.Em op Ns = Ns Ar ldl
.Ed
.Pp
when a UA happens along with fixing it,
so the faulting instruction can continue.
UA handling settings are inherited by child process.
Issued without any options,
.Nm
displays the current UA handling for the parent process.
.Pp
The options are as follows:
.Bl -tag -width Fl
.It Fl f
Unaligned access errors are not fixed for the parent and its future descendants.
.It Fl p
Unaligned access errors are not printed for the parent and its future
descendants.
.It Fl r
Resets the unaligned access error settings back to their bootup defaults.
.It Fl s
Unaligned access errors result in a
.Dv SIGBUS
being delivered to the parent and its future descendants.
This aids in pinpointing the faulting access so it can be debugged.
.El
.Sh DIAGNOSTICS
Exit status is 0 on success, and 1 if the command
fails for any reason.
.Sh COMPATIBILITY
The
.Nm
command syntax is incompatible with the DEC OSF/1 syntax.
.Sh SEE ALSO
.Xr signal 3
.Sh HISTORY
A
.Nm
utility first appeared in DEC OSF/1.
.Sh AUTHORS
.An -nosplit
The
.Fx
version of
.Nm
was originally written by
.An Andrew Gallatin Aq gallatin@cs.duke.edu
and modified by
.An David E. O'Brien Aq obrien@FreeBSD.org .
This
manual page was written by
.An David E. O'Brien Aq obrien@FreeBSD.org .