E-19
GUIDELINES FOR WRITING FPU EXCEPTIONS HANDLERS
SAVE_ENVIRONMENT ENDP
Example E-5. Reentrant Exception Handler
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LOCAL_CONTROL DW ?; ASSUME INITIALIZED
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REENTRANTPROC
;
; SAVE REGISTERS, ALLOCATE STACK SPACE FOR FPU STATE IMAGE
PUSH EBP
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MOV EBP, ESP
SUB ESP, 108 ; ALLOCATES 108 BYTES (32-bit PROTECTED MODE SIZE)
; SAVE STATE, LOAD NEW CONTROL WORD, RESTORE INTERRUPT ENABLE FLAG (IF)
FNSAVE[EBP-108]
FLDCW LOCAL_CONTROL
PUSH [EBP + OFFSET_TO_EFLAGS] ; COPY OLD EFLAGS TO STACK TOP
POPFD; RESTORE IF TO VALUE BEFORE FPU EXCEPTION
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;
; APPLICATION-DEPENDENT EXCEPTION HANDLING CODE GOES HERE. AN
UNMASKED EXCEPTION
; GENERATED HERE WILL CAUSE THE EXCEPTION HANDLER TO BE REENTERED.
; IF LOCAL STORAGE IS NEEDED, IT MUST BE ALLOCATED ON THE STACK.
;
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; CLEAR EXCEPTION FLAGS IN STATUS WORD (WHICH IS IN MEMORY)
; RESTORE MODIFIED STATE IMAGE
MOV BYTE PTR [EBP-104], 0H
FRSTOR[EBP-108]
; DE-ALLOCATE STACK SPACE, RESTORE REGISTERS
MOV ESP, EBP
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POP EBP
;
; RETURN TO POINT OF INTERRUPTION
IRETD
REENTRANT ENDP
