Module Name: src
Committed By: scole
Date: Mon Dec 26 19:46:59 UTC 2016
Modified Files:
src/sys/arch/ia64/ia64: context.S
Log Message:
Fix some comments and add new comment explaining probable bug in
cpu_switchto(). Not sure of a fix for it yet
To generate a diff of this commit:
cvs rdiff -u -r1.6 -r1.7 src/sys/arch/ia64/ia64/context.S
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/arch/ia64/ia64/context.S
diff -u src/sys/arch/ia64/ia64/context.S:1.6 src/sys/arch/ia64/ia64/context.S:1.7
--- src/sys/arch/ia64/ia64/context.S:1.6 Fri Aug 5 16:46:56 2016
+++ src/sys/arch/ia64/ia64/context.S Mon Dec 26 19:46:59 2016
@@ -1,4 +1,4 @@
-/* $NetBSD: context.S,v 1.6 2016/08/05 16:46:56 scole Exp $ */
+/* $NetBSD: context.S,v 1.7 2016/12/26 19:46:59 scole Exp $ */
/*
* Copyright (c) 2003 Marcel Moolenaar
@@ -821,7 +821,7 @@ ENTRY(cpu_switchto, 3)
* Save old context, unless the LWP is exiting.
*/
cmp.eq p6,p0=r0,in0 // p6 = (in0 == 0)
- add r14=PC_CURLWP,r13 // r2 = &ci->ci_curlwp
+ add r14=PC_CURLWP,r13 // r14 = &ci->ci_curlwp
;;
}
{ .mii
@@ -840,7 +840,7 @@ ENTRY(cpu_switchto, 3)
nop 0
/*
* Switch to new context, if p6 == true.
- * We assum to return to restorectx_return_here for swapped context.
+ * We assume to return to restorectx_return_here for swapped context.
*/
(p6) ld8 out0=[r3] // out0 = pcb of &newlwp
(p6) br.call.sptk.many rp=restorectx // if (p6) restorectx(out0)
@@ -855,7 +855,25 @@ ENTRY(cpu_switchto, 3)
br.call.sptk.many rp=swapctx
;;
}
-
+ /*
+ * XXX seems to be a bug here...
+ *
+ * swapctx() and restorectx() (which is called by swapctx())
+ * both adjust the bspstore (and hence bsp) registers. When
+ * returning to "restorectx_return_here:" the bspstore can
+ * be greater than bsp, a state known as an "Incomplete Register Frame".
+ *
+ * That is not necessarily fatal in itself, but apparently the RSE
+ * engine sets bsp=bspstore to adjust, which re-syncs the stacked
+ * registers (r32-r127). This clobbers our local registers below
+ * (loc0 and loc1) on the br return from swapctx(), and you get all
+ * kind of mysterious exceptions depeding on what gets restored from
+ * the backing store.
+ *
+ * Not sure of a proper fix is yet or how cpu_switchto should/can
+ * be interacting with restorectx()/swapctx()
+ *
+ */
restorectx_return_here:
{ .mib
mov r8=r9 // r8(ret0) = oldlwp
