Changes in kernel/arch/sparc64/src/context.S [245e8399:ecc83bd] in mainline

File:

• kernel/arch/sparc64/src/context.S (modified) (3 diffs)

kernel/arch/sparc64/src/context.S

@@ -28 +28 @@
 
 #include <arch/context_offset.h>
-#include <arch/arch.h>
-#include <arch/regdef.h>
+
+/**
+ * Both context_save_arch() and context_restore_arch() are
+ * leaf-optimized procedures. This kind of optimization
+ * is very important and prevents any implicit window
+ * spill/fill/clean traps in these very core kernel
+ * functions.
+ */
+        
+#include <arch/context_offset.h>
 
 .text   
@@ -36 +44 @@
 .global context_restore_arch
 
-/*
- * context_save_arch() is required not to create its own stack frame. See the
- * generic context.h for explanation.
- */
 context_save_arch:
-        #
-        # Force all our active register windows to memory so that we can find
-        # them there even if e.g. the thread is migrated to another processor.
-        #
-        flushw
-
         CONTEXT_SAVE_ARCH_CORE %o0
         retl
@@ -53 +51 @@
 context_restore_arch:
         #
-        # Forget all previous windows, they are not going to be needed again.
-        # Enforce a window fill on the next RESTORE instruction by setting
-        # CANRESTORE to zero and other window configuration registers
-        # accordingly. Note that the same can be achieved by executing the
-        # FLUSHW instruction, but since we don't need to remember the previous
-        # windows, we do the former and save thus some unnecessary window
-        # spills.
+        # Flush all active windows.
+        # This is essential, because CONTEXT_LOAD overwrites
+        # %sp of CWP - 1 with the value written to %fp of CWP.
+        # Flushing all active windows mitigates this problem
+        # as CWP - 1 becomes the overlap window.
         #
-        rdpr %pstate, %l0
-        andn %l0, PSTATE_IE_BIT, %l1
-        wrpr %l1, %pstate
-        wrpr %g0, 0, %canrestore
-        wrpr %g0, 0, %otherwin
-        wrpr %g0, NWINDOWS - 2, %cansave
-        wrpr %l0, %pstate
-
+        flushw
+        
         CONTEXT_RESTORE_ARCH_CORE %o0
         retl