; opcode c7 is Ev, Iz. c6 is Eb, Ib
    ; Eb: ModR/M to follow, byte
    ; consider 1100 011w : 11 000 reg : imm
    ; also consider 1011 w reg : imm for bytes

32-bit target, 8-bit source
  match =eax?, target
    db 0xB8
    dd source
  else match =edi?, target
    db 0xBF
    dd source

64-bit target, 32-bit source
  match =rax?, target            ; mov rax, 0x1234
    db 0x48, 0xC7, 0xC0
    dd source
;   48                           eAX REX.W prefix
;                                    (DEC is the 32-bit meaning, ignore it)
;                                    eAX -> register identifier,
;                                           width depends on operand
;                                    REX.W -> set 64-bit operand mode
;           c7                    Grp 11^1A - MOV Ev, Iz
;                                    immediate to register
;                                    1A -> bits 5,4,3 of ModR/M are opcode
;                                          extension
;                                    E -> modR/M byte to follow for operand
;                                    v -> word of appropriate size
;                                    I -> immediate data
;                                    z -> 32-bit operand
;              c0                ModR/M byte
;              0b11000000
;                11               mod: always 11
;                  000            op/reg: Mov Ev, Iz
;                     00x         w absent
;                       0         w (ignored)



  match =rdi, target             ; mov rdi, 0x1234
    db 0x48, 0xC7, 0xC7
    dd source
;   7:   48 c7 c7 2a 00 00 00    mov    $0x2a,%rdi
;   48                           eAX REX.W prefix
;                                    (DEC is the 32-bit meaning, ignore it)
;           c7                   Grp 11^1A - MOV Ev, Iz
;                                    immediate to register
;                                    1A -> bits 5,4,3 of ModR/M are opcode
;                                          extension
;                                    Ev -> ModR/M to follow for 32-bit operand
;                                    Iz -> Immediate data, 32-bits
;              c7                ModR/M byte
;              0b11000111
;                11               mod: always 11
;                  000            op/reg: Mov Ev, Iz
;                     11x         w present
;                       1         w true; use EDI



64-bit target, 64-bi source

  match =rdi, target             ; mov rdi, 0x1234
    db 0x48, 0xB8, 0x38
    dq source

  match =rsi, target
    db 0x48, 0xB8, 0x30
    dq source
    ; opcode c7 is Ev, Iz. c6 is Eb, Ib
    ; Eb: ModR/M to follow, byte
    ; consider 1100 011w : 11 000 reg : imm
    ; also consider 1011 w reg : imm for bytes