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Is pre-compiled ARM9 libs able to run on an ARM11 chip

Ping Ping Cheng
Note: This was originally posted on 15th October 2008 at http://forums.arm.com

Hi

I have couple pre-compiled libs in ARM9, is there a problem if link it with other ARM11 code and put on an ARM11 chip?

Thanks,
-ppj
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    Note: This was originally posted on 15th October 2008 at http://forums.arm.com

    I have couple pre-compiled libs in ARM9, is there a problem if link it with other ARM11 code and put on an ARM11 chip?


    Assuming this is some general application library, there should be no problem linking and running It in an ARM11 image. 

    There will probably be problems if the code contains anything specific for a chip (e.g. accessing CP14/15 registers not present in ARM11 maybe?)

    Also be aware that the code was built and scheduled for an ARM9 which may not necessarily be the best for an ARM11, so you may get better performance by rebuilding it for ARM11.
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    Note: This was originally posted on 16th October 2008 at http://forums.arm.com

    Just to reinforce what bhav said, you will get a signficant performance boost if you recompile for ARM11. In particular the ARM9 branch code scheduling is not usually "nice" to the the ARM11 branch predictor, so branches will be a lot more expensive.
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    Did you have a fix on this issue? I have the same problem with Pre-compiled ARM9 libs.

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    An architecture has an instruction set (possible assembler) that is 95-100% identical between CPUs in that architecture. Sometimes there are added instructions like a divide, more/extended floating point registers, etc. However, the intent is that a compiler can easily output code that will run on this set of CPUs (same architecture) with relative ease. Each new architecture tries to be backwards compatible with previous architectures.

    The main difference is that system registers may be quite different between CPUs even in the same architecture. So system/OS software will be quite different.

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    There will probably be problems if the code contains anything specific for a chip (e.g. accessing CP14/15 registers not present in ARM11 maybe?)