Gdb dump memory in specific region, save formatted output into a file

Question

I have a buggy (memory leaked) software. As an evidence, I have 1GB of core.dump file. Heap size is 900MB, so obviously, something allocates, but does not free the memory.

So, I have a memory region to examine like this.

(gdb) x/50000s 0x200000000

However, this is hard to guess only with naked eyes, which object or struct is not freed. My idea to trace is, "Save gdb formatted output into a file, and run a pattern match to see which magic string comes up the most." So, here is my question:

How can I save output of following command into a textfile, so that I can write an analyzer?

(gdb) x/10000000s 0x20000000    <-- I need this output into a file

Answer 1

You could use the "dump" function of gdb, see: https://sourceware.org/gdb/onlinedocs/gdb/Dump_002fRestore-Files.html

For your example:

dump binary memory result.bin 0x200000000 0x20000c350

This will give you a plain binary dump int file result.bin. You can also use the following to dump it in hex format:

dump ihex memory result.bin 0x200000000 0x20000c350

Using the dump command is much clearer than using the gdb logging hack (which even did not work for me somehow).