Hello,
is a chance to support fxsave64 and fxrstor64 (Intel® 64 and IA-32 Architectures Software Developer’s Manual Volume 2A: Instruction Set Reference, A-M, Order Number: 253666-033US, December 2009) in one of the next versions?

Thanks!
Helle

Helle,

Doesn't it already? In 64-bit mode fxsave compiles with 67 prefix just fine.

...and MenuetOS (64-bit) has been using it successfully for years.

Prefix 67h ? I see no effect... I use prefix 48h (REX.W) for e.g. "fxsave [rax]" (opcode "48 0f ae 00"). But REX.W + fxsave is fxsave64 (Intel). I use this in a fpu-monitor, with this I get in [rax+8] the large address of the last fpu-instruction. Without REX.W I get only a 32-bit-address (or nonsens) !
Greetings
Helle