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13.2 Programs compiled with -pg crash when run

Q: I cannot profile my program: when I compile it with -pg, it crashes or wedges my machine!

Q: When I compile my program with -pg, it runs much slower. Does the profiling code have such a huge overhead?

Q: I profiled my program, but the profile contains an entry _mono_putc which I don't use, and which eats up about 70% of execution time!

Q: When I run a profiled program on my dual (VGA+MDA) display system, the mono screen shows loads of meaningless numbers. Is there a way to stop this behavior?

A: DJGPP v2.01 has a bug in one of its library functions which is linked into your program when it is compiled with the -pg option. The bug is that the profiled program tries to write to the secondary mono screen, which caused the profiled programs to crash in many environments, in particular when a memory manager remaps some of the high memory. On systems which actually have the additional mono display, the profiled programs won't crash, but would run significantly slower and print debugging info on the mono display.

A patch which corrects this bug was posted to the DJGPP News group; you can find it by searching the DJGPP mail archives. DJGPP v2.02 and later includes a fixed version of the offending function, so upgrade to the latest version. A work-around is to run the program compiled with -pg on vanilla DOS configuration (no memory managers such as EMM386 or QEMM, and no Windows). However, when you use this work-around, your program might run much slower, although the profile that you get should not be affected.



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  Copyright 2001   by Eli Zaretskii     Updated Apr 2001