[PATCH v2 8/9] ARM: Thumb-2: Fix long-distance conditional branches in head.S for Thumb-2.

[Dave Martin]

Hi,

On Mon, Nov 22, 2010 at 7:17 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Mon, Nov 22, 2010 at 02:03:51PM -0500, Nicolas Pitre wrote:
>> On Mon, 22 Nov 2010, Dave Martin wrote:
>>
>> > The 32-bit conditional branches in Thumb-2 have a shorter range (+/-512K)
>> > than their ARM counterparts (+/-32MB).  The linker does not currently
>> > generate trampolines to extend the range of these Thumb-2 conditional
>> > branches, resulting in link errors when vmlinux is sufficiently large, e.g.:
>> >
>> > head.o:(.text+0x464): relocation truncated to fit: R_ARM_THM_JUMP19
>> >
>> > This patch forces the longer-range, unconditional branch encoding by
>> > use of an explicit IT instruction.  The resulting branches are triggered on
>> > the same conditions as before.
>> >
>> > Signed-off-by: Dave Martin <dave.martin at linaro.org>
>>
>> I'm afraid this patch is only making an actual bug visible.  There is no
>> reason why __error_p or __error_a ought to be farther than 512K away
>> from their call sites as they are all supposed to live in the __init
>> section close together.  It looks like the refactoring done in commit
>> 75d90832d5 has dropped the __init attribute from those moved functions,
>> and adding it back would be the real fix.
>
> No, you're not thinking right.  It was _intentional_ that __error_p
> ended up in a different section to __init.  With CPU hotplug, as it
> is called from the hotplug CPU initialization path, it needs to be
> available for that path to call.
>
> So it can't be thrown away with the init code when hotplug is enabled.
>
> The sections which the code end up in is correct as-is.
>

I will infer from this that the patch is useful/correct in its current state...

Let me know if anything needs to change.

Cheers
---Dave