Intel ARCHITECTURE IA-32 User Manual download pdf (Page 181)

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Vol. 3A 5-5

INTERRUPT AND EXCEPTION HANDLING

5.4 SOURCES OF EXCEPTIONS

The processor receives exceptions from three sources:

• Processor-detected program-error exceptions.

• Software-generated exceptions.

• Machine-check exceptions.

5.4.1 Program-Error Exceptions

The processor generates one or more exceptions when it detects program errors during the

execution in an application program or the operating system or executive. The IA-32 architec-

ture defines a vector number for each processor-detectable exception. Exceptions are classified

as faults, traps, and aborts (see Section 5.5, “Exception Classifications”).

5.4.2 Software-Generated Exceptions

The INTO, INT 3, and BOUND instructions permit exceptions to be generated in software.

These instructions allow checks for exception conditions to be performed at points in the

instruction stream. For example, INT 3 causes a breakpoint exception to be generated.

The INT n instruction can be used to emulate exceptions in software; but there is a limitation. If

INT n provides a vector for one of the IA-32 architecture exceptions, the processor generates an

interrupt to the correct vector (to access the exception handler) but does not push an error code

on the stack. This is true even if the associated hardware-generated exception normally produces

an error code. The exception handler will still attempt to pop an error code from the stack while

handling the exception. Because no error code was pushed, the handler will pop off and discard

the EIP instead (in place of the missing error code). This sends the return to the wrong location.

5.4.3 Machine-Check Exceptions

The P6 family and Pentium processors provide both internal and external machine-check mech-

anisms for checking the operation of the internal chip hardware and bus transactions. These

implementation dependent. When a machine-check error is detected, the processor signals a

machine-check exception (vector 18) and returns an error code.

See Chapter 5, “Interrupt 18—Machine-Check Exception (#MC)” and Chapter 14, “Machine-

Check Architecture,” for more information about the machine-check mechanism.

5.5 EXCEPTION CLASSIFICATIONS

Exceptions are classified as faults, traps, or aborts depending on the way they are reported and

whether the instruction that caused the exception can be restarted without loss of program or task

continuity.

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