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arrayscmemoryinitializationgdb

GDB initialize array with contents

I've not found what I am looking for, so I'll formulate my own question.

Consider the C-program below

char heap[<some-static-size>];

void main() {
  <this-code-reads-and-writes-to-heap>
}

I would like to execute this program in gdb, after first having initialized heap. One posibility is that i put the contents of the array in a file, and somehow feed that to gdb. How could I do this easiest? Once main is done, I would like to read the contents of heap and write it to some other file.

Solution

  • The GDB dump and restore commands can be used here. Set breakpoints at main and exit. Use &heap[0] as the start address.

    $ cat heap.c
char heap[100];

int main() {
    heap[0]++;
}

    $ dd if=/dev/random of=input.bin count=1 ibs=100
1+0 records in
0+1 records out
100 bytes copied, 0.000306025 s, 327 kB/s

    $ gdb -q heap
(gdb) b main
(gdb) commands
>restore input.bin binary &heap[0]
>continue
>end
(gdb) b exit
(gdb) commands
>dump binary memory output.bin &heap[0] &heap[100]
>continue
>end
(gdb) run
Breakpoint 1, main () at heap.c:4
4       heap[0]++;
Restoring binary file input.bin into memory (0x555555558040 to 0x5555555580a4)
Breakpoint 2, __GI__exit (status=0) at ../sysdeps/unix/sysv/linux/_exit.c:140
[Inferior 1 (process 9802) exited normally]
(gdb) q

    $ cmp -l input.bin output.bin
  1  52  53