Exceptions

Exceptions as described in this article are generated by the CPU when an 'error' occurs. Some exceptions are not really errors in most cases, such as page faults.

Exceptions are classified as:

• Faults: These can be corrected and the program may continue as if nothing happend.
• Traps: Traps are reported immediately after the execution of the trapping instruction.
• Aborts: Some severe unrecoverable error.

Name	Vector nr.	Type	Mnemonic	Error code?
Divide-by-zero Error	0	Fault	#DE	No
Debug	1	Fault/Trap	#DB	No
Non-maskable Interrupt	2	Interrupt	#NMI	No
Breakpoint	3	Trap	#BP	No
Overflow	4	Trap	#OF	No
Bound Range Exceeded	5	Fault	#BR	No
Invalid Opcode	6	Fault	#UD	No
Device Not Available	7	Fault	#NM	No
Double Fault	8	Abort	#NM	Yes
Coprocessor Segment Overrun	9	Fault	-	No
Invalid TSS	10	Fault	#TS	Yes
Segment Not Present	11	Fault	#NP	Yes
Stack-Segment Fault	12	Fault	#SS	Yes
General Protection Fault	13	Fault	#SS	Yes
Page Fault	14	Fault	#SS	Yes
Reserved	15	-	-	No
x87 Floating-Point Exception	16	Fault	#MF	No
Alignment Check	17	Fault	#AC	Yes
Machine Check	18	Abort	#MC	No
SIMD Floating-Point Exception	19	Fault	#XM/#XF	No
Reserved	20-29	-	-	No
Security Exception	30	-	#SX	No
Reserved	31	-	-	No

Exceptions

Faults

Divide-by-zero Error

The Divide-by-zero Error occurs when dividing any number by 0 using the DIV or IDIV instruction. Many OS developers use this exception to test whether their exception handling code works. This exception may also occur when the result is too large to be represented in the destination.

The instruction pointer points to the DIV or IDIV instruction which caused the exception.

Bound Range Exceeded

This exception can occur when the BOUND instruction is executed. The BOUND instruction compares an array index with the lower and upper bounds of an array. When the index is out of bounds, the Bound Range Exceeded exception occurs.

The instruction pointer points to the BOUND instruction which caused the exception.

Traps

Debug

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Breakpoint

A Breakpoint exception occurs at the execution of the INT3 instruction. Some debug software replace an instruction by the INT3 instruction. When the breakpoint is trapped, it replaces the INT3 instruction with the original instruction, and decrements the instruction pointer by one.

The instruction pointer points to the byte after the INT3 instruction.

Overflow

An Overflow exception is raised when the INTO instruction is executed while the overflow bit in RFLAGS is set to 1.

The instruction pointer points to the instruction after the INTO instruction.

Misc

Non-maskable Interrupt

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