According to the Intel manual:
***In 64-bit mode, r/m8 can not be encoded to access the following byte registers if a REX prefix is used: AH, BH, CH, DH.
So mov R8B,BH can't assemble. I know that.
%use smartalign
ALIGNMODE generic,16
BITS 64
section .text
mov R8B,BH ; assembly error
mov AH,AL ; no assembly error
mov BH,BPL ; assembly error
nasm -f macho64 xx.s -o xx.o
xx.s:7: error: cannot use high register in rex instruction
xx.s:9: error: cannot use high register in rex instruction
This is in 64-bit mode. mov AH,AL assembles. The third move gets the cannot use high register in rex instruction error.
Is this correct? I don't believe that mov BH,BPL generates a REX prefix. Is this a NASM bug?
Edit: Well, I'm seeing from other sources that BPL requires a REX prefix. I didn't know that or rather it didn't sink in. So I'll have to move my register assignments around.
