Debugging C with Cosmopolitan Libc

&gt; Cosmopolitan Libc allows you to log every function call over the program’s execution – just pass --ftrace at the end of your program, like this:<p>&gt; .&#x2F;hex16.com .&#x2F;missing.txt --ftrace<p>That seems like magic. It seems you have to build with a special flag that tells GCC to put a nop at the start of each function. Then, before main runs, Cosmopolitan sees the --ftrace on the command line, and modifies the code in memory to replace those nops with calls to something that does the logging. See <a href="https:&#x2F;&#x2F;justine.lol&#x2F;ftrace&#x2F;" rel="nofollow">https:&#x2F;&#x2F;justine.lol&#x2F;ftrace&#x2F;</a>.

I&#x27;m fascinated specifically with how Justine must have collected the knowledge to write Cosmopolitan. I know some guys who play around with PEs and virtual memory manually, but I always wonder what sort of interests lead you to discovering this sort of thing.<p>I suspect the combination of interests is a little out there. For instance, with game cheat developers, you tend to first at least have some interest in C++, then understanding memory scanning, then signature scanning, trampolining, and all of a sudden you have the skillset ingredients for authoring some rudimentary cheats. Advanced skills come with driver development, which you then pick up to figure out how to evade anti-cheat technology, etc.<p>But very few developers I know say, oh yeah, I was just interested directly in this sort of thing from the get-go and decided to pick up all of the specific skills to go straight to cheat development.<p>Usually, it&#x27;s the guys who already have game development experience.<p>What in the world did Justine see before Cosmopolitan? Maybe debugging tech? An interest in creating her own libc and understanding syscalls? Just fascinating.

What&#x27;s the advantage over calling gdb yourself?

If anyone&#x27;s interested in how this actually works, take a look at this (originally linked) article: <a href="https:&#x2F;&#x2F;justine.lol&#x2F;ape.html" rel="nofollow">https:&#x2F;&#x2F;justine.lol&#x2F;ape.html</a><p>This reminds me a little bit about how &quot;Wine&quot; works, but because the support doesn&#x27;t involve &quot;everything an OS has to provide&quot; the footprint is smaller.

so where does the machine code for the TUI live? does it get compiled into your binary? how big is it?

I&#x27;ve read that you can use Cosmopolitan to write C++ as well.<p>Can you use similar features with C++ development?

Perhaps I am missing something but what does this have to with Cosmopolitan?

I wonder if it would be possible to have a kind of logging function which would work similarly as the --ftrace? That would reduce significantly the no-trace cpu cost.