Instructions (basically identical to 32-bit x86)For gory instruction set details, read the full Intel PDFs: part 1 (A-M) and part 2 (N-Z).
Mnemonic
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Purpose
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Examples
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mov dest,src
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Move data between registers, load immediate data into registers, move data between registers and memory.
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mov rax,4 ; Load constant
into rax
mov rdx,rax ; Copy rax into rdx
mov rdx,[123] ; Copy rdx to memory address 123
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push src
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Insert a value onto the stack. Useful for passing arguments, saving registers, etc.
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push rbp
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pop dest
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Remove topmost value from
the stack. Equivalent to "mov dest, [rsp]; add 8,rsp"
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pop rbp
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call func
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Push the address of the next instruction and start executing func.
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call print_int
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ret
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Pop the return program counter, and jump there. Ends a subroutine.
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ret
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add dest,src
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dest=dest+src
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add rax,rdx ; Add rbx to rax
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mul src
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Multiply rax and src as unsigned integers, and put the result in rax. High 64 bits of product (usually zero) go into rdx.
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mul rdx ; Multiply rax by rdx
; rax=low bits, rdx overflow
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div src
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Divide rax by src, and put the ratio into rax, and the remainder into rdx.
Bizarrely, on input rdx must be zero, or you get a SIGFPE.
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mov rdx,0 ; avoid error
div rcx ; compute rax/rcx
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shr val,bits
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Bitshift a value right by a
constant, or the low 8 bits of rcx ("cl").
Shift count MUST go in rcx, no other register will do!
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add rcx,4
shr rax,cl ; shift by rcx
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| jmp label |
Goto the instruction label:. Skips anything else in the way. |
jmp post_mem
mov [0],rax ; Write to NULL!
post_mem: ; OK here... |
cmp a,b
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Compare two values. Sets
flags that are used by the conditional jumps (below).
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cmp rax,10
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jl label |
Goto label
if previous comparison came out as less-than. Other conditionals
available are: jle (<=), je (==), jge (>=), jg (>), jne (!=),
and many others.
Also available in unsigned comparisons: jb (<), jbe (<=), ja (>), jae (>=).
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jl loop_start ; Jump if rax<10
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Constants, Registers, Memory
"12" means decimal 12;
"0xF0" is hex. "some_function" is the address of the first
instruction of the function.
Memory access (use register as pointer): "[rax]". Same as C "*rax".
Memory access with offset (use register + offset as pointer): "[rax+4]". Same as C "*(rax+4)".
Memory access with scaled index (register + another register * scale):
"[rax+rbx*4]". Same as C "*(rax+rbx*4)".
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Registers
rax, rcx, rdx, rbx, rsp, rbp, rsi, rdi, r8, r9, r10, r11, r12, r13, r14,
and r15.
Registers can be accessed via a variety of names and sizes:
64-bit: rax, r8
32-bit: eax, r8d (plus zero extension)
16-bit: ax, r8w
8-bit: al, r8b
rsp is the stack pointer
The stack frame pointer isn't used very often.
Return value in rax (or eax)
Arguments are in rdi, rsi, rdx, rcx, r8d, r9d, and then on the stack (in
the usual order)
Saved registers are rsp,rbp, rbx, r12, r13, r14, and r15.
All other registers can be trashed.
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