Changeset 48f89683 in rtems for cpukit/score/ChangeLog

Timestamp:

05/14/02 17:45:36 (21 years ago)

Author:

Joel Sherrill <joel.sherrill@…>

Branches:

4.10, 4.11, 4.8, 4.9, 5, master

Children:

19131e97

Parents:

06549dcf

Message:

2001-05-14 Till Straumann <strauman@…>

• src/threaddispatch.c, src/threadhandler.c: Per PR211 fix saving/restoring floating point context. The fpsave and fprestore routines are only used in a executing context which _is_ fp and hence has the FPU enabled. The current behavior required the FPU always to be on which is very dangerous if lazy context switching is used. [Joel Note: Some ports explicitly enabled the FPU in the FP save and restore routines to avoid this.]

The patch also makes sure (on powerpc only) that the FPU is disabled
for integer tasks. Note that this is crucial if deferred fp context
switching is used. Otherwise, fp context corruption may go undetected!
Also note that even tasks which merely push/pop FP registers to/from
the stack without modifying them still MUST be FP tasks - otherwise
(if lazy FP context switching is used), FP register corruption (of
other, FP, tasks may occur)!

Furthermore, (on PPC) by default, lazy FP context save/restore
is _disabled_.

File:

• cpukit/score/ChangeLog (modified) (1 diff)

cpukit/score/ChangeLog

@@ +1 @@
+2001-05-14      Till Straumann <strauman@slac.stanford.edu>
+
+        * src/threaddispatch.c, src/threadhandler.c: Per PR211 fix
+        saving/restoring floating point context.  The fpsave and fprestore
+        routines are only used in a executing context which _is_ fp and hence
+        has the FPU enabled. The current behavior required the FPU always to
+        be on which is very dangerous if lazy context switching is used.  
+        [Joel Note: Some ports explicitly enabled the FPU in the FP save and
+        restore routines to avoid this.]
+
+        The patch also makes sure (on powerpc only) that the FPU is disabled
+        for integer tasks. Note that this is crucial if deferred fp context
+        switching is used. Otherwise, fp context corruption may go undetected!
+        Also note that even tasks which merely push/pop FP registers to/from
+        the stack without modifying them still MUST be FP tasks - otherwise
+        (if lazy FP context switching is used), FP register corruption (of
+        other, FP, tasks may occur)!
+
+        Furthermore, (on PPC) by default, lazy FP context save/restore
+        is _disabled_.
+
 2001-04-26      Joel Sherrill <joel@OARcorp.com>