Re: [Patch ARM Gas] - strexh/strexb warn for bad addressing modes.

[Luke <hazelnusse at gmail dot com>]

You are correct, the behavior is undefined and your patch does the
right thing.  I'll pass this along to the CMSIS folks and give them a
heads up.

~Luke

On Thu, Sep 22, 2011 at 5:59 AM, James Greenhalgh
<james.greenhalgh@arm.com> wrote:
> Hi,
>
>> If you read this literally, it only says STREX has the restriction that
>> you've added to gas, and that it doesn't apply to any of the other ones
>> (in
>> particular STREXH and STREXB). ÂI'm not sure if this is the same across
>> all
>> the ARM7/9/11 processors, but it certainly seems that this should be an
>> allowed instruction for Cortex M3, given that they are shipping this
>> instruction with their CMSIS stuff.
>
> In my copy of the ARMARMv7M [0] strexb, strexh and strex are all listed
> as UNPREDICTABLE when rd == rt || rd == rn.
>
> I would read the quoted passage of the User Guide Reference Material
> as saying Â"for Store-Exclusive Instructions, Rd must be different
> from both Rt and Rn". Which better fits with the description in the
> ARMARM.
>
> There is potentially an argument for making these UNPREDICTABLE behaviours
> warnings, but this would just mask the real issue, which, IMHO is
> that the library is not sufficiently cautious with the registers it uses
> for these instructions.
>
> If you want further advice on the CMSIS libraries I would suggest going
> through your normal CMSIS support channels.
>
> Regards
> James Greenhalgh
>
> [0] -
> http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0403c/index.h
> tml
>
>
>
>



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