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Second-chance exceptions cannot be ignored, because the program cannot continue running. If you encounter second-chance exceptions while debugging malware, there may be bugs in the malware that are causing it to crash, but it is more likely that the malware doesn’t like the environment in which it is running.
There are several common exceptions. The most common exception is one that occurs when the INT 3 instruction is executed. Debuggers have special code to handle INT 3 exceptions, but OSs treat these as any other exception.
Programs may include their own instructions for handling INT 3 exceptions, but when a debugger is attached, it will get the first chance. If the debugger passes the exception to the program, the program’s exception handler should handle it.
Single-stepping is also implemented as an exception within the OS. A flag in the flags register called the trap flag is used for single-stepping. When the trap flag is set, the processor executes one instruction and then generates an exception.
A memory-access violation exception is generated when code tries to access a location that it cannot access. This exception usually occurs because the memory address is invalid, but it may occur because the memory is not accessible due to access-control protections.
Certain instructions can be executed only when the processor is in privileged mode. When the program attempts to execute them outside privileged mode, the processor generates an exception.
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