What does Movzbl mean?
What does Movzbl mean?
move a byte with zero
● so movzbl means: move a byte with zero extension into 32-bit (“l”) register; last byte of. register is that byte, all others are zero. ● (zero extension means to put zeroes into the remaining unused bytes of the register)
What is %RBX used for?
Registers
| Register | Purpose | Saved across calls |
|---|---|---|
| %rbx | callee-saved | Yes |
| %rcx | used to pass 4th argument to functions | No |
| %rdx | used to pass 3rd argument to functions | No |
| %rsp | stack pointer | Yes |
What is CLTQ instruction?
The cltq instruction is a specialized movs that operates on %rax . This no-operand instruction does sign-extension in-place on %rax ; source bitwidth is l, destination bitwidth is q. cltq # operates on %rax, sign-extend 4-byte src to 8-byte dst, shorthand for movslq êx,%rax.
What do parentheses mean in assembly?
The parentheses indicate the move instruction should consider the value in rbp to be a memory address, that it should move the value 42 to the memory address referenced by rbp (or actually to the memory address four bytes before the value of rbp ) and not into rbp itself.
What is Repz RETQ?
So, repz is a prefix that repeats the following instruction until some register is 0. Also, it only works on string instructions; otherwise the behavior is undefined.
What is rip Assembly?
The instruction pointer register (%rip) points to the next instruction to execute; it cannot be directly accessed by the programmer, but is heavily used as the base for position-independent code addressing.
What does CLTQ do in assembly?
cltq promotes an int to an int64. shl 3, %rax makes an offset to a 64-bit pointer (multiplies whatever is in rax by 8). what the code is doing is looping through a list of pointers to environment variables. when it finds a value of zero, that’s the end, and it drops out of the loop.
What does JMPQ do in assembly?
it generates an instruction to load 32-bits (the size of register eax) from memory at address of msg .
What does Movl do in assembly?
movl (%ebx, %esi, 4), %eax. Multiply the contents of number register %esi by 4 and add the result to the contents of number register %ebx to produce a memory reference. Move the contents of this memory location into number register %eax.
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