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Optimization on ARM 9

Posted by Bill Bracken on July 17, 2009
I have a working application created using GNU compiler (not sure what version) when optimized for size (-O1). However when optimizatin is removed (-O0) the application no longer functions. Data declared within a function (i.e., on the stack) get mangled. Any thoughts.

bb

RE: Optimization on ARM 9

Posted by Richard on July 17, 2009
I think you need to find the compiler version.

I have seen something similar only in the Cortex M3 application where C code is used to clear the RAM to zero during the start routine. When optimisation was on the look counter used was held in a register and it worked fine. When optimisation was off the variable was held on the stack and it too got cleared by the loop as the RAM was being written to.

Regards.

RE: Optimization on ARM 9

Posted by Bill Bracken on July 20, 2009
Richard,

Thanks for the response. What did you do to correct the issue. The application runs with -o0, appears to run. For example, it can communicate with a PC via the serial interface. I was in the process of debugging a CAN driver when I noticed the problem. A variable on the stack was used to itterate through an array. After update the variable and then calling a function (within the class) on return from the function the variable was incorrect. Stepping through the code didn't seem to corrupt the value. The person who did the port indicated that initially the port didn't run at all if optimization was turned off.

Thanks,
bb

RE: Optimization on ARM 9

Posted by Bill Bracken on July 20, 2009
Richard,

GNU compiler. Version 3.1.1. They are reluctant to update to a newer version.

bb


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