CS 208 reference sheet

bits-reference.png

Assembly Instructions

mov a, b Copy from a to b.
movs a, b Copy from a to be with sign extension. Needs two width specifiers.
movz a, b Copy from a to be with zero extension. Needs two width specifiers.
lea a, b Compute address and store in b. Note: the scaling parameter of memory operands can only be 1, 2, 4, or 8.
push src Push src onto the stack and decrement stack pointer.
pop dst Pop from the stack into dst and increment stack pointer.
call <func> Push return address onto stack and jump to a procedure.
ret Pop return address and jump there.
add a, b Add a to b and store in b (and set condition codes).
sub a, b Subtract a from b (compute b - a) and store in b (and set condition codes).
imul a, b Multiply a and b and store in b (and set condition codes).
neg a Compute -a according to 2's complement and store in a (and set condition codes).
and a, b Bitwise AND of a and b, store in b (and set condition codes).
or a, b Bitwise OR of a and b, store in b (and set condition codes).
xor a, b Bitwise XOR of a and b, store in b (and set condition codes).
sar a, b Shift value of b right (arithmetic) by a bits, store in b (and set condition codes).
shr a, b Shift value of b right (logical) by a bits, store in b (and set condition codes).
shl a, b Shift value of b left by a bits, store in b (and set condition codes).
sal a, b Shift value of b left by a bits, store in b (and set condition codes).
cmp a, b Compare b with a (compute b - a), set condition codes based on result (result is not stored).
test a, b Bitwise AND of a and b, set condition codes based on result (result is not stored).
jmp <label> Unconditional jump to address.
jCOND <label> Considtion jump based on condition codes .
setCOND a Set byte a to 0 or 1 based on condition codes.

 

Operands

Form Value Name
$NUM Literal value of NUM Immediate
%REG Value stored in REG Register
NUM Value stored at address NUM Absolute
(%REG) Value stored at address in REG Indirect
NUM(%REG) Value stored at address REG + NUM Base + displacement
(%REG_B, %REG_I) Value stored at address REG_B + REG_I Indexed
NUM(%REG_B, %REG_I) Value stored at address REG_B + REG_I + NUM Indexed
(, %REG, S) Value stored at address REG * S Scaled indexed
NUM(, %REG, S) Value stored at address REG * S + NUM Scaled indexed
(%REG_B, REG_I, S) Value stored at address REG_B + REG_I * S Scaled indexed
NUM(%REG_B, REG_I, S) Value stored at address REG_B + REG_I * S + NUM Scaled indexed

Conditionals

Instruction     (op) s, d test a, b cmp a, b
je sete "Equal" d (op) s == 0 b & a == 0 b == a
jne setne "Not equal" d (op) s != 0 b & a != 0 b != a
js sets "Sign" (negative) d (op) s < 0 b & a < 0 b - a < 0
jns setns (non-negative) d (op) s >= 0 b & a >= 0 b - a >= 0
jg setg "Greater" d (op) s > 0 b & a > 0 b > a
jge setge "Greater or equal" d (op) s >= 0 b & a >= 0 b >= a
jl setl "Less" d (op) s < 0 b & a < 0 b < a
jle setle "Less or equal" d (op) s <= 0 b & a <= 0 b <= a
ja seta "Above" (unsigned >) d (op) s > 0U b & a > 0U b - a > 0U
jb setb "Below" (unsigned <) d (op) s < 0U b & a < 0U b - a < 0U

Registers and Sizes

Name Convention Lowest 4 bytes Lowest 2 bytes Lowest byte
%rax Return value %eax %ax %al
%rbx   %ebx %bx %bl
%rcx Argument #4 %ecx %cx %cl
%rdx Argument #3 %edx %dx %dl
%rsi Argument #2 %esi %si %sil
%rdi Argument #1 %edi %di %dil
%rsp Stack pointer %esp %sp %spl
%rbp   %ebp %bp %bpl
%r8 Argument #5 %r8d %r8w %r8b
%r9 Argument #6 %r9d %r9w %r9b
%r10   %r10d %r10w %r10b
%r11   %r11d %r11w %r11b
%r12   %r12d %r12w %r12b
%r13   %r13d %r13w %r13b
%r14   %r14d %r14w %r14b
%r15   %r15d %r15w %r15b
C type x86-64 suffix Size in bytes
char b 1
short w 2
int l 4
long q 8