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About c : Include-source-code-of-mallocc-in-gdb

Question Detail

How can I include/view the source code of malloc in gdb?

I want to do a step by step execution in gdb, and step into malloc.c source code when any of the malloc functions is called.

Currently what gdb says is:
malloc.c: No such file or directory.

This guy here faced the same problem, but they do not mention a solution, ie how to actually step into the source code of malloc.

I am on Ubuntu server 14.04, and I have already tried to install the following:
libc6-dbg, libc6-dev, and libc6-dbgsym.
I don’t even know if one of these packages might help, but installing the libc-dbgsym gives me the following error:

dpkg: error processing archive /var/cache/apt/archives/libc6-dbgsym_2.19-0ubuntu6.6_amd64.ddeb (--unpack):  trying to overwrite
    '/usr/lib/debug/usr/lib/x86_64-linux-gnu/audit/sotruss-lib.so', which
    is also in package libc6-dbg:amd64 2.19-0ubuntu6.6 dpkg-deb: error:
    subprocess paste was killed by signal (Broken pipe)

Question Answer

The following worked for me. Not sure whether there is a better way.

  1. Install libc6-dbg (which you have already done):
    sudo apt-get install libc6-dbg
  2. Install the eglibc-source package (ubuntu actually uses eglibc): sudo apt-get install eglibc-source.
  3. Unpack the tar file that was installed in /usr/src/glibc: /usr/src/glibc $ sudo tar xvf eglibc-2.19.tar.xz
  4. Crank up gdb and add in the path to the malloc source: (gdb) dir /usr/src/glibc/eglibc-2.19/malloc

(gdb) n

13 char *c = malloc(100);

(gdb) s

__GI___libc_malloc (bytes=100) at malloc.c:2876 2876



Gdb can only show the source codes because the debug-compiled binaries contain references between the binary code and the source files.

malloc() is in the C library. On normal systems, it is not compiled with debug metadata, and its sources are also not installed in the system.

But they are reachable, you only need to install the debug versions of these libraries. For example, on debian an apt-get install glibc-debug or similar will do it. On SuSE, a zipper in libc6-debug (afaik, maybe the exact package names could be a little bit differ).

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