Intel 64 and IA-32 Architectures Software Developers Manual Volume 1, Basic Architecture

Vol. 1 D-21
GUIDELINES FOR WRITING X87 FPU EXCEPTION HANDLERS
POPFD ;RESTORE IF TO VALUE BEFORE x87 FPU EXCEPTION
;
;APPLICATION-DEPENDENT EXCEPTION HANDLING CODE GOES HERE
;
;CLEAR EXCEPTION FLAGS IN STATUS WORD (WHICH IS IN MEMORY)
;RESTORE MODIFIED ENVIRONMENT IMAGE
MOV BYTE PTR [EBP-24], 0H
FLDENV [EBP-28]
;DE-ALLOCATE STACK SPACE, RESTORE REGISTERS
MOV ESP, EBP
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POP EBP
;
;RETURN TO INTERRUPTED CALCULATION
IRETD
SAVE_ENVIRONMENT ENDP
Example D-5. Reentrant Exception Handler
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LOCAL_CONTROL DW ?; ASSUME INITIALIZED
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REENTRANTPROC
;
;SAVE REGISTERS, ALLOCATE STACK SPACE FOR x87 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 x87 FPU EXCEPTION
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