[maemo-developers] Java acceleration/Jazelle

[From: Sebastian Mancke]

Sebastian Mancke schrieb:
> Hi Simon,
> 
> sincerely I don't found the time to test your code yet.
> 
>> Did you make a typo in your declaration (on p34) of int code[]? Should
>> this not be unsigned char code[] as bytecodes are 1x byte not n x byte
>> long (I'm assuming you're running on a machine with sizeof(int)>1)?
> This is not a typo. I don't understand the reason, but it had only
> worked with the integer array, not with bytes - don't know why.

reasoning a minute, it sounds logical to me to have an int array,
since normal arm instructions are 32bit long.
So stretching the byte code to 4byte, the instructions and pc can
internaly be handled as in normal arm operation mode.


> 
> --Sebastian
> 
> Simon Pickering schrieb:
>> Hi all,
>>
>> Sebastian, in this link:
>>
>>> You can find a small example in my jalimo slides from linuxtag2007
>>> (slide 33ff).
>>>
>>> http://www.jalimo.org/wiki/doku.php?id=news:linuxtag2007 
>> (direct link:
>> http://www.jalimo.org/documents/jalimo-slides_english_linuxtag2007.pdf)
>>
>> Did you make a typo in your declaration (on p34) of int code[]? Should this not
>> be unsigned char code[] as bytecodes are 1x byte not n x byte long (I'm assuming
>> you're running on a machine with sizeof(int)>1)? Just wondering if this is a
>> typo when you were writing the presentation or whether it might have affected
>> your results. On the other hand it may be my misunderstanding the declaration.
>>
>>> It might be possible to test at least some aspects of my 'new improved' 
>>> theory. The one that comes to mind is to try a BXJ to an unhandled Java 
>>> instruction immediately. This should then branch back to whatever ARM 
>>> code is at R12 straight away (not needing to know the pointer table 
>>> base address). This could prove a number of things, including 
>>> the stack pointer, R12 & R14 contents, etc.
>> I've written a piece of test code, but not tested it yet (no compiler here at
>> work). I must admit that I've only learned extended inline asm this week, so it
>> may not work correctly ;). If anyone spots any mistakes, please let me know.
>>
>> http://people.bath.ac.uk/enpsgp/nokia770/jazelle/test_jazelle.c
>> http://people.bath.ac.uk/enpsgp/nokia770/jazelle/to_compile_do_this.txt
>>
>> I'll post some results tomorrow/later on, one way or the other.
>>
>> Cheers,
>>
>>
>> Si
>>
> 
> 


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