| Message ID | 1371645406-16873-3-git-send-email-ben.dooks@codethink.co.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Dear Ben Dooks, On Wed, 19 Jun 2013 13:36:38 +0100, Ben Dooks wrote: > +#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 > +#else > bic ip, ip, #0x000000ff > orr ip, ip, r6 @ mask in offset bits 31-24 > +#endif > str ip, [r7, r3] > 2: cmp r4, r5 > ldrcc r7, [r4], #4 @ use branch for delay slot As was suggested in http://lists.infradead.org/pipermail/linux-arm-kernel/2013-February/150782.html, you could put this patch later in the series and use the ARM_BE8() macro you introduce in the next patch. Also in http://lists.infradead.org/pipermail/linux-arm-kernel/2013-February/150784.html, the same reviewer suggested to name the macro BE8() to make it fit like ARM() and THUMB() in the margin left by the indentation of assembly code. And also to add LE() to make the above code look like: BE8( bic ip, ip, #0xff000000) BE8( orr ip, ip, r6, lsl#24) LE( bic ip, ip, #0x000000ff) LE( orr ip, ip, r6) Thomas
On 19/06/13 18:33, Thomas Petazzoni wrote: > Dear Ben Dooks, > > On Wed, 19 Jun 2013 13:36:38 +0100, Ben Dooks wrote: > >> +#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 >> +#else >> bic ip, ip, #0x000000ff >> orr ip, ip, r6 @ mask in offset bits 31-24 >> +#endif >> str ip, [r7, r3] >> 2: cmp r4, r5 >> ldrcc r7, [r4], #4 @ use branch for delay slot > > As was suggested in > http://lists.infradead.org/pipermail/linux-arm-kernel/2013-February/150782.html, > you could put this patch later in the series and use the ARM_BE8() > macro you introduce in the next patch. > > Also in > http://lists.infradead.org/pipermail/linux-arm-kernel/2013-February/150784.html, > the same reviewer suggested to name the macro BE8() to make it fit like > ARM() and THUMB() in the margin left by the indentation of assembly > code. And also to add LE() to make the above code look like: > > BE8( bic ip, ip, #0xff000000) > BE8( orr ip, ip, r6, lsl#24) > LE( bic ip, ip, #0x000000ff) > LE( orr ip, ip, r6) Actually, that doesn't work as LE is not the inverse of BE8 as it could also be when the kernel is being compiled in BE32.
Dear Ben Dooks, On Thu, 20 Jun 2013 11:54:58 +0100, Ben Dooks wrote: > > Also in > > http://lists.infradead.org/pipermail/linux-arm-kernel/2013-February/150784.html, > > the same reviewer suggested to name the macro BE8() to make it fit like > > ARM() and THUMB() in the margin left by the indentation of assembly > > code. And also to add LE() to make the above code look like: > > > > BE8( bic ip, ip, #0xff000000) > > BE8( orr ip, ip, r6, lsl#24) > > LE( bic ip, ip, #0x000000ff) > > LE( orr ip, ip, r6) > > Actually, that doesn't work as LE is not the inverse of BE8 as > it could also be when the kernel is being compiled in BE32. Aah, correct. In BE32, data and instructions have the same endianness. Thanks, Thomas
diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S index 8bac553..56ddd47 100644 --- a/arch/arm/kernel/head.S +++ b/arch/arm/kernel/head.S @@ -594,8 +594,14 @@ __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 +#else bic ip, ip, #0x000000ff orr ip, ip, r6 @ mask in offset bits 31-24 +#endif str ip, [r7, r3] 2: cmp r4, r5 ldrcc r7, [r4], #4 @ use branch for delay slot
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. Note, not tested against an actual bug, it looked wrong. Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk> --- arch/arm/kernel/head.S | 6 ++++++ 1 file changed, 6 insertions(+)