Registers
FIXME.
- the first half of this lecture should be an ever expanding view of the registers
- this should include examples of where r’s and smaller’s are used
- the second half is how to use division
- needs to include shifts and xor
Add Function (Arithmetic)
add.c
int add(int x, int y) {
return x + y;
}
\(\leftrightarrow\)
clang -S add.c
add:
mov %edi, %eax
add %esi, %eax
retq
Arithmetic Instructions
x86-64
add src, dst
sub src, dst
imul src, dst
\(\leftrightarrow\)
C Pseudocode
dst += src
dst -= src
dst *= src
src is register/immediate/memory
dst is register/memory
Division
Division-Related Instructions
x86-64
idivq denom
cqto
\(\leftrightarrow\)
C Pseudocode
%rax = (%rdx:%rax) / denom
%rdx = (%rdx:%rax) mod denom
%rdx:%rax = (int128_t)%rax
denom is a register
idiv simultaneously finds the remainder and the quotient
a:b means “concatenate the bits of a and b to get a single number”
FIXME. write problem about the following code:
mov $10, %rax
idiv %rax
which gives Floating point exception (core dumped) when run.
FIXME. talk about xor for some reason TBD (needed for next notes)