How to debug a foobar Program Counter

I was immediately suspicious of the crash. A Floating Point Exception in a method whose only arithmetic was a "divide by sizeof(short)".

I looked at the stack crawl & saw that the offset into the method was "+91". Then I examined a disassembly of that method & confirmed that the Program Counter was in fact foobar at the time of the crash. The disassembly showed instructions at +90 and +93 but not +91.

This is a method, 32-bit x86 instructions, that gets called very frequently in the life of the application. This crash has been reported 3 times.

How does this happen? How do I set a debugging trap for the开发者_JS百科 situation?

Generally when you fault in the middle of an instruction, its due to bad flow control(ie: a broken jump, call, retn), an overflow, bad dereferencing or your debug symbols being out-of-sync making the stack trace show incorrect info. Your first step is to reliably reproduce the error everytime, else you'll have trouble trapping it, from there I'd just run it in a debugger, force the conditions to make it explode, then examine the (call) stack and registers to see if they are valid values etc.