This is because there are no encodings to access those parts in any instruction.Īssuming it is not possible, what are the reasons behind this?Īs noted by in the comments below, it is simply defined so in the manuals. You'll have to use indirect instruction sequences if you're interested in doing that. It is impossible to access the higher parts of the EAX and RAX registers, or of any other 32 and 64-bit registers, directly. Is it possible to access the higher part of the 32-bit and 64-bit registers? If so, which ones? Note: I am talking about direct access to these bytes, I am not asking for a sequence of instructions that could retrieve them. Assuming it is not possible, what are the reasons behind this?.Is it possible to access the higher part of the 32-bit and 64-bit registers? If so, which ones?.But I couldn't find any reference for the rax and eax higher parts. One can easily access the higher and lower part of ax by referencing to ah and al respectively. Here's an example regarding the rax 64-bit register and its subsequent divisions: 6 3 1 I was wondering whether there was any way to access the higher part of the registers. With the evolution of CPU architecture, register size was extended, from 8, to 16, 32, and eventually 64-bit. I don't know whether this is a silly question, but I couldn't find any answer.
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