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80386 Programmer's Reference Manual -- Opcode VERR |
VERR, VERW -- Verify a Segment for Reading or Writing
OperationIF segment with selector at (r/m) is accessible with current protection level AND ((segment is readable for VERR) OR (segment is writable for VERW)) THEN ZF := 0; ELSE ZF := 1; FI; DescriptionThe two-byte register or memory operand of VERR and VERW contains the value of a selector. VERR and VERW determine whether the segment denoted by the selector is reachable from the current privilege level and whether the segment is readable (VERR) or writable (VERW). If the segment is accessible, the zero flag is set to 1; if the segment is not accessible, the zero flag is set to 0. To set ZF, the following conditions must be met:
Flags AffectedZF as described aboveProtected Mode ExceptionsFaults generated by illegal addressing of the memory operand that contains the selector, the selector is not loaded into any segment register, and no faults attributable to the selector operand are generated#GP(0) for an illegal memory operand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code) for a page fault Real Address Mode ExceptionsInterrupt 6; VERR and VERW are not recognized in Real Address ModeVirtual 8086 Mode ExceptionsSame exceptions as in Real Address Mode; #PF(fault-code) for a page fault
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