[PATCH 03/14] ARM: fixup_pv_table bug when CPU_ENDIAN_BE8

[Will Deacon]

On Wed, Jul 24, 2013 at 04:24:34PM +0100, Ben Dooks wrote:
> On 24/07/13 15:33, Will Deacon wrote:
> > On Wed, Jul 24, 2013 at 11:27:51AM +0100, Ben Dooks wrote:
> >> The fixup_pv_table assumes that the instructions are in the same
> >> endian configuration as the data, but when the CPU is running in
> >> BE8 the instructions stay in little-endian format.
> >>
> >> Make sure if CONFIG_CPU_ENDIAN_BE8 is set that we do all the
> >> alterations to the instructions taking in to account the LDR/STR
> >> will be swapping the data endian-ness.
> >>
> >> Since the code is only modifying a byte, we avoid dual-swapping
> >> the data, and just change the bits we clear and ORR in (in the
> >> case where the code is not thumb2).
> >>
> >> For thumb2, we add the necessary rev16 instructions to ensure that
> >> the instructions are processed in the correct format, as it was
> >> easier than re-writing the code to contain a mask and shift.
> >>
> >> Signed-off-by: Ben Dooks<ben.dooks at codethink.co.uk>
> >> ---
> >>   arch/arm/kernel/head.S |    8 ++++++++
> >>   1 file changed, 8 insertions(+)
> >>
> >> diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> >> index 8bac553..e40c0b3b 100644
> >> --- a/arch/arm/kernel/head.S
> >> +++ b/arch/arm/kernel/head.S
> >> @@ -584,8 +584,10 @@ __fixup_a_pv_table:
> >>   	b	2f
> >>   1:	add     r7, r3
> >>   	ldrh	ip, [r7, #2]
> >> +ARM_BE8(rev16	ip, ip)
> >>   	and	ip, 0x8f00
> >>   	orr	ip, r6	@ mask in offset bits 31-24
> >> +ARM_BE8(rev16	ip, ip)
> >
> > I'm not sure I follow you when you say this is easier than a mask and a
> > shift? As far as I can tell, it's two extra instructions and makes the LE
> > and BE cases look different.
> 
> I am not as familiar with THUMB2 as the ARM, so it was easier
> to do this than see if there where any spare registers to hold the
> mask and shift values, and use them.

What's wrong with the following?

Will

--->8

diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index 9cf6063..ee660c2 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -581,8 +581,13 @@ __fixup_a_pv_table:
        b       2f
 1:     add     r7, r3
        ldrh    ip, [r7, #2]
+#ifdef CONFIG_CPU_ENDIAN_BE8
+       and     ip, 0x008f
+       orr     ip, ip, r6, lsl #24
+#else
        and     ip, 0x8f00
        orr     ip, r6  @ mask in offset bits 31-24
+#endif
        strh    ip, [r7, #2]
 2:     cmp     r4, r5
        ldrcc   r7, [r4], #4    @ use branch for delay slot