Re: [Xen-devel] [PATCH v2 19/20] livepatch/elf: Adjust section aligment to word

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 25/08/16 16:11, Jan Beulich wrote:
> > > > On 25.08.16 at 15:37, <konrad.wilk@xxxxxxxxxx> wrote:
> > On most architectures it does not matter what the aligment is.
> >
> > On ARM32 it is paramount that the aligment is word-size (4)
> > otherwise we get a Data Abort when trying to perform ELF
> > relocations. That is due to ARM 32 only being able to write to
> > word-aligned addresses.
Well, it is the same on ARM64. However we decided to disable the 
alignment check (SCTLR.A not set) because some of the primitives 
imported from Linux (e.g memcpy) rely on the hardware handling misalignment.
In any case, I would not recommend to use unaligned access on ARM as 
they may have a big performance impact.
> That's not exactly true, afaik: ARM can write to byte- and
> half-word-aligned addresses, but only bytes/half-words.
That's correct.

Regards,

--
Julien Grall

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