Subject: CVS commit: syssrc/sys/arch/alpha/alpha
To: None <>
From: Nathan J Williams <>
List: source-changes
Date: 09/07/2001 00:20:44
Module Name:	syssrc
Committed By:	nathanw
Date:		Thu Sep  6 21:20:44 UTC 2001

Modified Files:
	syssrc/sys/arch/alpha/alpha: vm_machdep.c

Log Message:
Remove the infamous "DANGER WILL ROBINSON: FEN SET in cpu_fork!"
diagnostic. It's not indicative of an error condition.

The code sequence in question calls fpusave_proc(), which ultimately
calls alpha_pal_wrfen(0), which clears the FEN bit in the current
PCB. However, the diagnostic message is based on reading that bit from
the PCB representation in memory, which is not guaranteed to be kept
up-to-date with respect to the real PCB contents. According to the
AARM, third edition, II-B 4.2:

"If the PCB is read while ownership resides with the processor, it is
UNPREDICTABLE whether the original or an updated value of a field is

The Alpha architecture does not provide a way to read the true value
of the FEN bit of the current PCB, so the test is simply removed.

To generate a diff of this commit:
cvs rdiff -r1.73 -r1.74 syssrc/sys/arch/alpha/alpha/vm_machdep.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.