Comment by throwaway2037

11 hours ago

I would like the see the source code for libmymalloc.so, however, I don't see anything in the blog post. Nor do I see anything in his GitHub profile: https://github.com/jsikstro

Also, I cannot find his email address anywhere (to ask him to share it on GitHub).

Am I missing something?

6 comments

throwaway2037

joelsiks 11 hours ago

The exact implementation of mymalloc isn't relevant to the post. I have an old allocator published at https://github.com/joelsiks/jsmalloc that I did as part of my Master's thesis, which uses a similar debug-logging mechanism that is described in the post.

nly 11 hours ago

dlsym() with the RTLD_NEXT flag basically:

https://catonmat.net/simple-ld-preload-tutorial-part-two

There's actually a better way to hook GNUs malloc:

https://www.man7.org/linux/man-pages/man3/malloc_hook.3.html

This is better because you can disable the hook inside the callback, and therefore use malloc within your malloc hook (no recursion)

But you can't use this mechanism before main()

Joker_vD 10 hours ago

    The use of these hook functions is not safe in multithreaded
    programs, and they are now deprecated.  From glibc 2.24 onwards,
    the __malloc_initialize_hook variable has been removed from the
    API, and from glibc 2.34 onwards, all the hook variables have been
    removed from the API.  Programmers should instead preempt calls to
    the relevant functions by defining and exporting malloc(), free(),
    realloc(), and calloc().

nly 8 hours ago

Yeah. Shame though because it gave you the option to control exactly when you hooked and didn't hook, which let stop and start debugging allocations based on arbitrary triggers.
The global variable approach was very useful and pretty low overhead.

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