From: nowhere@nospicedham.never.at   
      
   On 07.08.2021 17:51, R.Wieser wrote:   
   ...   
   > and for some reason I can't get the FXSAVE to work (my assembler shows its   
   > age by not knowing the opcode, and trying to use a "db 0Fh,0AEH, ....."   
   > sequence crashes the program).   
      
   on older CPUs  0F AE xx will raise exception 6 [illegal opcode] if:   
      
   1) bit 5 of xx is 1  (xx 20..3F, 60..7F, A0..BF)   
      newer CPU may show a few valid instructions (see sandpile.org)   
      
   2) mod=3 aka register operand (C0..FF) [memory only!]   
      
   3) may raise EXC_6 if not supported   
       0F AE 90..97 98..9f  mean STMXCSR LDMXCSR [support specific]   
      
   so I'd recommend either   
       0F AE 06 00 xx  FXSAVE [xx00h]  (needs 512 byte DS: buffer !)   
   or shorter   
       0F AE 00        FXSAVE [bx+si]  (ditto)   
   or HLL styled :)   
       0F AE 46 00     FXSAVE [bp+0]   (needs 512 byte on SS: stack)   
   __   
   wolfgang   
      
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