[softwarelist] Re: DPScan + ARMini -> crash?
- From: Peter Bell <peter@xxxxxxxxxxxxxxxxx>
- To: davidpilling@xxxxxxxxxxxxx
- Date: Sun, 10 Jul 2011 01:10:10 +0800
On Saturday, 09 July, 2011 10:12 PM, David Pilling wrote:
So we did a test with printfs inserted, and the bug went away.
Functionally the debug version is the same as the one that crashes, but
it will have lots of side effects like calling OS routines.
This reminds me of a problem I once experienced, working in Fortran in a
DEC PDP11 environment. The program was crashing, or corrupting data - I
don't remember exactly, now.
However, we couldn't find the fault - a detailed walk through the code
didn't reveal anything, if we added extra statements in an attempt to
trace it, the fault went away. If we compiled and built with the system
debugger enabled, the fault went away ... ultimately, this led us to the
real cause - enabling the debugger disabled the compiler's code
optimisation.
The fault was being introduced by a bug in the optimiser - examination
of the generated machine code allowed us to identify the precise point
of failure, which was not exactly where we expected to find it, because
the optimiser had changed the sequence of the instructions.
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