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6-50 Vol. 3
INTERRUPT AND EXCEPTION HANDLING
Interrupt 13—General Protection Exception (#GP)
Exception Class Fault.
Description
Indicates that the processor detected one of a class of protection violations called
“general-protection violations.” The conditions that cause this exception to be gener-
ated comprise all the protection violations that do not cause other exceptions to be
generated (such as, invalid-TSS, segment-not-present, stack-fault, or page-fault
exceptions). The following conditions cause general-protection exceptions to be
generated:
• Exceeding the segment limit when accessing the CS, DS, ES, FS, or GS
segments.
• Exceeding the segment limit when referencing a descriptor table (except during a
task switch or a stack switch).
• Transferring execution to a segment that is not executable.
• Writing to a code segment or a read-only data segment.
• Reading from an execute-only code segment.
• Loading the SS register with a segment selector for a read-only segment (unless
the selector comes from a TSS during a task switch, in which case an invalid-TSS
exception occurs).
• Loading the SS, DS, ES, FS, or GS register with a segment selector for a system
segment.
• Loading the DS, ES, FS, or GS register with a segment selector for an execute-
only code segment.
• Loading the SS register with the segment selector of an executable segment or a
null segment selector.
• Loading the CS register with a segment selector for a data segment or a null
segment selector.
• Accessing memory using the DS, ES, FS, or GS register when it contains a null
segment selector.
• Switching to a busy task during a call or jump to a TSS.
• Using a segment selector on a non-IRET task switch that points to a TSS
descriptor in the current LDT. TSS descriptors can only reside in the GDT. This
condition causes a #TS exception during an IRET task switch.
• Violating any of the privilege rules described in Chapter 5, “Protection.”
• Exceeding the instruction length limit of 15 bytes (this only can occur when
redundant prefixes are placed before an instruction).
• Loading the CR0 register with a set PG flag (paging enabled) and a clear PE flag
(protection disabled).