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Global variable alignment Rate Topic: -----

#1 User is offline   jms 

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Posted 13 January 2011 - 07:38 AM

Hi,

I am working with RealView Compilation Tools v2.1. I need to align a static global variable on a 16-byte boundary. In the 'Compiler and Libraries Guide' document, section 3.1.3, the __align(n) keyword is explained. It is not clear to me if n=16 is allowed for a static global variable. I have tried it and it appears to be working, but I would like to confirm it.

Best Regards,
Miguel
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#2 User is offline   jms 

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Posted 17 January 2011 - 01:19 PM

Hi,

I have not received any answers, can someone help me on this?

Regards,
Miguel
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#3 User is offline   isogen74 

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Posted 17 January 2011 - 05:33 PM

For RVCT 2.1 it is only specified to work for alignments of 1,2,4, or 8 - it is unclear what happens for alignments larger than this, although I suspect it is not guaranteed to do anything predictably.

FYI - in newer tool releases (RVCT4.1) it will work for the following alignments of n:

  • For local variables, n can take the values 1, 2, 4, or 8.
  • For global variables, n can take any value up to 0x80000000 in powers of 2.

When optimizing software, consider that the quickest code to run is the bit you removed from the call path.
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#4 User is offline   jms 

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Posted 19 January 2011 - 02:28 PM

Hi,

The point is that RVCT 2.1 says: 'You can specify a power of two for the alignment boundary, however eight is the maximum for auto variables'. As I understand, an 'auto' variable is the same as a 'local' variable, so it is not clear to me what is the limitation for global variables.

Regards,
Miguel
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