windows 结构化异常处理机制

Common Errors & Approaches to Error Checking
• Common Errors
– Failure of new to allocate requested memory – Array index out of bounds – Division by zero – Function received invalid parameters
• Software-generated exception
– INT n instruction generates an exception with an exception number (n) as an operand
Interrupts vs Exceptions
– Interrupt (device generated)
• Error handling should be used for
– processing exceptional situations – processing exceptions for components that cannot handle them directly – processing exceptions for widely used components (libraries, classes, functions) that should not process their own exceptions – large projects that require uniform error processing
•
Language level.
• • • Type conversion; illegal values, improper casts. Bounds violations; illegal array indices. Bad references; null pointers.
•
Program level.
–
–
TLB miss, page fault, protection
divide by zero, invalid opcode, misaligned access
Illegal operations
–
Trap
• Return to the next instruction (after the trapping instruction)
• User defined exceptions.
What:
• Interrupts • Exception • Interrupts vs Exception
Interrupts
• Interrupts
– Forced transfer of control to a procedure (handler) due to external events (interrupts) or due to an erroneous condition (exceptions)
– Procedure
• When an interrupt is received or an exception condition detection, the current task is suspended and transfer automatically goes to a handler • After the handler is complete, the interrupted task resumes without loss of continuity, unless recovery is not possible or the interrupt causes the currently running task to be terminated.
• Severe errors or malfunctions • Abort handlers are designed to collect diagnostic information about the processor’s state and then perform a graceful system shutdown • Examples: bit error (parity error), inconsistent or illegal values in system tables
– – – – The try, catch, and throw Statements Unhandled C++ Exceptions When to use exception handle Good Programming Style with C++ Exceptions
• Mechanism • Performance
• Interrupt handling mechanism
– Allows interrupts/exceptions to be handled transparently to the executing process (application programs and operating system)
– Non-maskable interrupt (NMI)
• Cannot be disabled by program • Received on the processor’s NMI# input pin
– Software interrupt
• Generated by INT n instruction – INT instruction can be used to generate an interrupt or an exception by using a vector number as an operand • Viewed as an implicit call to interrupt handler of interrupt vector n • No mechanism for masking interrupts
Exception
– Abort
• Suspend the process at an unpredictable location
– Does not report the precise location of the instruction causing the exception e program
– For a JMP instruction, the next instruction should point to the target of the JMP instruction
• •
Reported immediately following the execution of the trapping instruction Examples: breakpoint, debug, overflow
Agenda
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Where:
Exceptions can occur at many levels:
•
Hardware/operating system level.
• • Arithmetic exceptions; divide by 0, under/overflow. Memory access violations; segfault, stack over/underflow.
• Approaches to Error Checking
– Ignore the possibility – Handle the error where it occurs
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Easy to observe the error handling code
When Exception Handling Should Be Used
– Exceptions
• Processor-detected
– Faults – correctable (restartable); e.g. page fault – Traps – no reexecution needed; e.g. breakpoint – Aborts – severe error; process usually terminated (by signal)
Exception
• Exception Classification (processor-generated)
– Fault
• • • • Return to the faulting instruction Reported during the execution of the faulting instruction Virtual memory faults
• Maskable: device-generated, associated with IRQs (interrupt request lines); may be temporarily disabled (still pending) • Nonmaskable: some critical hardware failures
Exception in windows
How:
• C++ Exception Handling • Structure Exception Handling
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C++ Exception
• Common Errors & Approaches to Error Checking • Use Exception handle
Introduction of Exception Handling in windows