Quiz Entry - updated: 2026.07.14
What does mov (%rsp), %eax vs mov %rsp, %rax mean?
Parentheses mean "dereference" — (%rsp) reads memory at that address; without them, %rsp is just the register's value (the address itself).
# eax = value stored at address rsp points to (reads memory)
mov (%rsp), %eax
# rax = the address itself (rsp's value, no memory read)
mov %rsp, %rax
| Instruction | Meaning | Analogy in C |
|---|---|---|
mov (%rsp), %eax |
Read memory at rsp | eax = *rsp |
mov %rsp, %rax |
Copy the pointer itself | rax = rsp |
mov 8(%rsp), %eax |
Read memory at rsp+8 | eax = *(rsp + 8) |
lea 8(%rsp), %rax |
Compute address rsp+8 | rax = rsp + 8 (no read) |
This is the most fundamental distinction in assembly: parentheses = memory access, no parentheses = register-to-register.
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