CODEWITHSUNDEEP
cassembly
Doug Asker
Doug Asker

Reputation: 41

Need help using gdb with my C program

I am learning assembly language. I am using gdb to learn about how to get information from the C code that is written. I am trying to see the rip register at the beginning of each line and see how many bytes of machine code are in each of the C statements in this program? Can anyone show me the commands in gdb to find these?

#include <stdio.h>

int main(void) {
    register int wye;
    int *ptr;
    int ex;

    ptr = &ex;
    ex = 305441741;
    wye = -1;
    printf("Enter an integer: ");
    scanf("%i", ptr);
    wye += *ptr;
    printf("The result is %i\n", wye);

    return 0;
}

Upvotes: 4

Views: 168

Answers (1)

Chris Dodd
Chris Dodd

Reputation: 126110

Short example of stuff you can do to see some things about your program. $ is the shell prompt and gdb> is the gdb prompt, so don't type those:

$ gdb myprogram
    ... info about gdb and myprogram
gdb> disas main
    ... disassembly of the main function
gdb> break main
    ... sets a breakpoint in main; you see a message about this probably calling it breakpoint 1
gdb> run
    ... program starts and stops immediately at the start of main
gdb> i r
    ... lots of info about register contents
gdb> p $rip
    ... current instruction pointer (assuming x86_64)
gdb> s
    ... program runs for one source line.
gdb> p $rip
    ... ip has advanced a bit.

Upvotes: 1

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