Why can’t I move directly a byte to a 64 bit register?

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  1. What’s the purpose of the LEA instruction?
  2. What considerations go into predicting latency for operations on modern superscalar processors and how can I calculate them by hand?
  3. Why does the x86-64 / AMD64 System V ABI mandate a 16 byte stack alignment?
  4. Why in x86-64 the virtual address are 4 bits shorter than physical (48 bits vs. 52 long)?
  5. Is a sign or zero extension required when adding a 32bit offset to a pointer for the x86-64 ABI?
  6. How do RIP-relative variable references like “[RIP + _a]” in x86-64 GAS Intel-syntax work?
  7. Printing floating point numbers from x86-64 seems to require %rbp to be saved
  8. How to print a single-precision float with printf
  9. MOVZX missing 32 bit register to 64 bit register
  10. Why are signed and unsigned multiplication different instructions on x86(-64)?
  11. What do the E and R prefixes stand for in the names of Intel 32-bit and 64-bit registers?
  12. Why is the address of static variables relative to the Instruction Pointer?
  13. Why is (or isn’t?) SFENCE + LFENCE equivalent to MFENCE?
  14. Why NASM on Linux changes registers in x86_64 assembly
  15. Distinguishing memory from constant in GNU as .intel_syntax
  16. Why does this MOVSS instruction use RIP-relative addressing? [duplicate]
  17. How to push a 64bit int in NASM?
  18. What are the names of the new X86_64 processors registers?
  19. x64 instruction encoding and the ModRM byte
  20. Assembly registers in 64-bit architecture
  21. How to multiply a register by 37 using only 2 consecutive leal instructions in x86?
  22. what does “mov offset(%rip), %rax” do?
  23. What does “rep; nop;” mean in x86 assembly? Is it the same as the “pause” instruction?
  24. When should I use size directives in x86?
  25. Load from a 64-bit address into other register than rax
  26. Why does this code execute more slowly after strength-reducing multiplications to loop-carried additions?
  27. x86 32 bit opcodes that differ in x86-x64 or entirely removed
  28. Can rip be used with another register with RIP-relative addressing?
  29. Create an arg array for execve on the stack
  30. x86 Assembly pushl/popl don’t work with “Error: suffix or operands invalid”

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