Stefan Reinauer (stefan.reinauer@coreboot.org) just uploaded a new patch set to gerrit, which you can find at http://review.coreboot.org/9183
-gerrit
commit c863c96fc2f806a785d193b86e4492a6d1b6adb8 Author: Vadim Bendebury vbendeb@chromium.org Date: Fri Oct 3 09:47:13 2014 -0700
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 --- src/arch/mips/bootblock.S | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
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 @@ _start: /* 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. */