mips: do not place branch instructions in branch delay slot
A branch instruction in a branch delay slot confuses the execution
pipeline and causes an exception.
bootblock.S was written 'by hand', has a branch instruction in branch
delay slot and includes '.set noreorder' directive, which causes it to
crash when trying to branch to main().
Adding a nop instruction fixes the problem. Also adding a nop after
the last branch in the file just in case main() returns and the object
linked next starts with a branch.
BUG=chrome-os-partner:31438
TEST=Running on the simulator can reach main() now
Change-Id: I0882b2eb5ce426f5a311018ffbb6f37a2ca64d98
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/221421
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/9183
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
Tested-by: build bot (Jenkins)
diff --git a/src/arch/mips/bootblock.S b/src/arch/mips/bootblock.S
index dbde803..f369e00 100644
--- a/src/arch/mips/bootblock.S
+++ b/src/arch/mips/bootblock.S
@@ -39,6 +39,10 @@
/* Run main */
b main
- /* Should never return from main. */
-2:
+ /*
+ * Should never return from main. Make sure there is no branch in the
+ * branch delay slot.
+ */
+2: nop
b 2b
+ nop /* Make sure there is no branch after this either. */