Computer
Systems

Spring 2013
course
navigation

Feb 19

OK, it's time to learn x86 Assembly - chapter 3 of Systems textbook.
Discuss assigned reading and problems 3.1 through 3.5 :
Then work through some real assembler code
Questions :
/* swap.c ... based on CMU system's course lecture 4 * * $ gcc -O1 -m32 swap.c -o swap * * $ gdb swap * (gdb) start * (gdb) disass swap * Dump of assembler code for function swap: * 0x08048394 <+0>: push %ebp * 0x08048395 <+1>: mov %esp,%ebp * 0x08048397 <+3>: push %ebx * 0x08048398 <+4>: mov 0x8(%ebp),%edx * 0x0804839b <+7>: mov 0xc(%ebp),%eax * 0x0804839e <+10>: mov (%edx),%ecx * 0x080483a0 <+12>: mov (%eax),%ebx * 0x080483a2 <+14>: mov %ebx,(%edx) * 0x080483a4 <+16>: mov %ecx,(%eax) * 0x080483a6 <+18>: pop %ebx * 0x080483a7 <+19>: pop %ebp * 0x080483a8 <+20>: ret * (gdb) break *(swap +4) * (gdb) continue * (gdb) info stack * #0 0x08048398 in swap () * #1 0x080483cf in doit () * #2 0x080483df in main () * (gdb) info frame * Stack level 0, frame at 0xbffff608: * eip = 0x8048398 in swap; saved eip 0x80483cf * called by frame at 0xbffff628 * Arglist at 0xbffff600, args: * Locals at 0xbffff600, Previous frame's sp is 0xbffff608 * Saved registers: * ebx at 0xbffff5fc, ebp at 0xbffff600, eip at 0xbffff604 * (gdb) print $eip * $1 = (void (*)()) 0x8048398 <swap+4> * (gdb) x/32x $esp * 0xbffff5fc: 0xb7fceff4 0xbffff620 0x080483cf 0xbffff61c * 0xbffff60c: 0xbffff618 0xb7e9ad35 0xb7ff0a70 0x000001c8 * 0xbffff61c: 0x0000007b 0xbffff628 0x080483df 0xbffff6a8 * 0xbffff62c: 0xb7e81e37 0x00000001 0xbffff6d4 0xbffff6dc * 0xbffff63c: 0xf57fe414 0xffffffff 0xb7ffeff4 0x08048215 * 0xbffff64c: 0x00000001 0xbffff690 0xb7fefa51 0xb7fffad0 * 0xbffff65c: 0xb7fe09d0 0x00000001 0xb7fceff4 0x00000000 * 0xbffff66c: 0x00000000 0xbffff6a8 0x58a166bb 0x7776feab * (gdb) x/32d $esp * 0xbffff5fc: -1208160268 -1073744352 134513615 -1073744356 * 0xbffff60c: -1073744360 -1209422539 -1208022416 456 * 0xbffff61c: 123 -1073744344 134513631 -1073744216 * 0xbffff62c: -1209524681 1 -1073744172 -1073744164 * 0xbffff63c: -176167916 -1 -1207963660 134513173 * 0xbffff64c: 1 -1073744240 -1208026543 -1207960880 * 0xbffff65c: -1208088112 1 -1208160268 0 * 0xbffff66c: 0 -1073744216 1486972603 2004287147 * (gdb) quit */ void swap(int *xp, int *yp){ int t0 = *xp; int t1 = *yp; *xp = t1; *yp = t0; } int doit(){ int x = 123; int y = 456; swap(&x, &y); return x + y; } int main(){ int z = doit(); return 0; }
As time allows, continue with material from that chapter :

midterm in about two weeks

Bomblab ...
http://cs.marlboro.edu/ courses/ spring2013/systems/ notes/ Feb_19
last modified Monday February 18 2013 11:58 pm EST

attachments [paper clip]

     name last modified size
[COD]swap.c Feb 18 2013 11:47 pm 2.88kB