From b92e54333f75baa86bcda67b1beeb19669250f03 Mon Sep 17 00:00:00 2001 From: Vadim Bendebury Date: Fri, 3 Oct 2014 09:47:13 -0700 Subject: 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 Reviewed-on: https://chromium-review.googlesource.com/221421 Reviewed-by: Aaron Durbin Reviewed-on: http://review.coreboot.org/9183 Reviewed-by: Ronald G. Minnich Tested-by: build bot (Jenkins) --- src/arch/mips/bootblock.S | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) (limited to 'src/arch') diff --git a/src/arch/mips/bootblock.S b/src/arch/mips/bootblock.S index dbde803b14..f369e006fa 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. */ -- cgit v1.2.3