Re: [Xen-devel] [PATCH v1 3/8] xen/arm: Support sign-extension for every read access

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2015-09-29 at 12:13 +0100, Julien Grall wrote:
> > Or is it, couldn't we be updating a byte in the middle of the word?
> 
> *r is a register, the byte/half-word/word... are always living in the
> lowest bit of the register.

So just to check:

ldrs* do support e.g odd offsets, but given a 32 bit MMIO region which
reads 0xAABBCCDD then when reading from offset 1 at this point *r contains
0x000000CC already (and not 0x0000C00) and sign extending the lowest byte
is therefore correct.

Right?


> 
> > Probably figuring out the correct assertion is more hassle than it is
> > worth..
> 
> I would rather skip it.
> 
> [1] http://www.open-std.org/jtc1/sc22/WG14/www/docs/n1256.pdf
> 

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