glosarium asm
enum option_e {
STOP = 'q',
CONTINUE = 'c',
NEW = 'n',
EDIT = 'e',
DELETE = 'd'
}
int main(){
char optionbuf[4];
while(optionbuf[0] != STOP){
scanf("%4s, optionbuf);
switch (optionbuf[0]){
case NEW:
handleNew();
break;
case EDIT:
handleEdit();
break;
case DELETE:
handleDelete();
break;
case STOP:
handlestop();
break;
case CONTINUE:
handleContinue();
break;
default;
break;
}
how it goes
122f: call 1090 <__isoc99)scanf@plt>
1234: movzx eax, BYTE PTR [rbp-0xc] : moving zero extended of BYTE PTR to eax
1238: movsx eax, al: moving sign extended of last significant byte that came from eax
123b: sub eax, 0x63: subtract 0x63 (case from our value which is "c") with eax from BYTE PTR that processed by moving sign extended and moving zero extended we did before
123e: cmp eax, 0xe: compared 0xe with eax that we've been processed above (dunno what are 0xe really is)
1241: ja 12a2 <main+0xa6>: jump above to 12a2 stack entries, if comparison (value under of 0xe) doesn't meet
1259: lea rdx, [rip+0xe00] : load-ea with specific address is 0xe00 from 1241 into rdx
explanation of user input as negative index value:
(little endian)0xfffff242 => 4294963778: is a big chunk
0xffffffff(max size 32bit represent) - 0xfffff242 => 3517 is 123b: sub eax, 0x63 command substraction kind above
hex(3517+1) => 0xdbe: result is negative hex-dbe
rdx of 1259 then result 2054
# 2054 <_IO_stdin_used+0x54>
1260: add rax, rdx: add rdx from jump table to rax(2054)
2054 is rdx then added to rax which would compute (subtract) later on with 0xdbe
hex(0x2054-0xdbe) => 0x1296
