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

Will Deacon
2013-07-24T14:33:35Z

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@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.

> strh ip, [r7, #2]
> 2: cmp r4, r5
> ldrcc r7, [r4], #4 @ use branch for delay slot
> @@ -594,8 +596,14 @@ __fixup_a_pv_table:
> #else
> b 2f
> 1: ldr ip, [r7, r3]
> +#ifdef CONFIG_CPU_ENDIAN_BE8
> + @ in BE8, we load data in BE, but instructions still in LE
> + bic ip, ip, #0xff000000
> + orr ip, ip, r6, lsl#24

Pedantry: you could add a space between lsl and #24.

Will