By the following very short garden path:1. How silly to write such a thing in C from scratch. Such a project will invariably invent half of Lisp in order to have the right kind of infrastructure for doing this and that.2. Let&#x27;s look for some of it up and down the tree. Oh look, there is a bitset and hashmap, see? I don&#x27;t see test cases for these anywhere; is it original work from this project or battle-tested code taken from elsewhere?3. Open hashmap.c ...GPL violation found in half a minute.

I&#x27;m not them, but it does straight up say in hashmap.c that the code was copied from <a href="https:&#x2F;&#x2F;github.com&#x2F;git&#x2F;git&#x2F;blob&#x2F;master&#x2F;hashmap.c">https:&#x2F;&#x2F;github.com&#x2F;git&#x2F;git&#x2F;blob&#x2F;master&#x2F;hashmap.c</a>, which is under the GPL license.

I&#x27;m curious, how did you notice this?Do you have a scanner that checks these sorts of things or is it something that you are passionate about?

You&#x27;ve used GPL2 code taken from git (hashmap.c) in your Apache 2.0 project.<a href="https:&#x2F;&#x2F;opensource.stackexchange.com&#x2F;questions&#x2F;10737&#x2F;inclusion-of-gpl-2-0-code-into-my-apache-2-0-program" rel="nofollow">https:&#x2F;&#x2F;opensource.stackexchange.com&#x2F;questions&#x2F;10737&#x2F;inclusi...</a>

In multi-threaded mode, each thread will create a separate memory pool. If in single-threaded mode, a global memory pool is used. You can refer to <a href="https:&#x2F;&#x2F;github.com&#x2F;neocanable&#x2F;garlic&#x2F;blob&#x2F;72357ddbcffdb756416dd2fc1481f8c22be1c2c5&#x2F;src&#x2F;libs&#x2F;memory&#x2F;mem_pool.c">https:&#x2F;&#x2F;github.com&#x2F;neocanable&#x2F;garlic&#x2F;blob&#x2F;72357ddbcffdb75641...</a>. The x_alloc and x_alloc_in in it indicate where the memory is allocated. When each task ends, the memory allocated in the memory pool is released, and the cycle repeats.

That might be true, but leaking is neither the critical nor the most hard to find memory management issue, and good luck trying to adapt or even run valgrind with a codebase that mindlessly allocates and leaks everywhere.

Many command line tools do not need memory management at all, at least to first approximation. Free nothing and let the os cleanup on process exit. Most libraries can either use an arena internally and copy any values that get returned to the user to the heap at boundaries or require the user to externally create and destroy the arena. This can be made ergonomic with one macro that injects an arena argument into function defs and another that replaces malloc by bumping the local arena data pointer that the prior macro injected.

Thank god Lisp is older than C, don&#x27;t have to deal with such nonsense :-)

That’s impossible. Just be more careful and everything should work, the author’s C was just a bit rusty!

Yes, perhaps it could have a marketing slogan like &quot;Write once, crash everywhere!&quot;

I think he is using memory pools, so this is ok.

If only there were a couple of OSes implementated during the 1960&#x27;s with such programming languages....

Interesting. Someone should come up with a language that prevents these sorts of mistakes!

In the same file:<pre><code> static bool is_java_identifier_start(char c)
 {
 return (isalpha(c) || c == &#x27;_&#x27; || c == &#x27;$&#x27;);
 }
</code></pre>
Undefined behavior in isalpha if c happens to be negative (and not equal to EOF), like some UTF-8 byte.I think some &lt;ctype.h&gt; implementations are hardened against this issue, but not all.

&gt; I am always curious how different C programs decide how to manage memory.At a basic level, you can create memory on the stack or on the heap. Obviously I will focus on the heap as that is dynamically allocating memory of a certain size.The C programming language does not force you how to handle memory. You are pretty much on your own. For some C programmers (and likely more inexperienced ones) they will malloc individual variables like they are creating a &#x27;new&#x27; instance in a typical OOP language like Java. This can be a telltale sign of a programmer working with C that comes from an OOP background. As they learn and improve on their C skills they realise they should create a chunk of memory of a certain type, but could still be malloc(ing) and free(ing) all over the code, making it difficult to understand what is being used and where -- especially if you are looking at code you did not write.You can also have programs that do not bother free(ing) memory. For example, a simple shell program that just does simple input-&gt;process-&gt;output and terminates. For these types of programs, just let the OS deal with freeing the memory.Good C code (in my opinion) uses malloc and free in only a handful of functions. There are higher level functions for proper Allocators. One example is an Arena Allocator. Then if you want a function which may require dynamic memory, you can tell it which allocator to use. It gives you control, generally speaking. You can create a simple string library or builder with an allocator.Of course an Allocator does not have to use memory on the heap. It can still use on the stack as well.There are various other patterns to use in the world of memory, especially in C.

Strings! The bane of C programming, and a big reason I prefer C++. :D

I am always curious how different C programs decide how to manage memory.In this case there are is a custom string library. Functions returned owned heap-allocated strings.However, I think there&#x27;s a problem where static strings are used interchangably with heap-allocated strings, such as in the function `string class_simple_name(string full)` ( <a href="https:&#x2F;&#x2F;github.com&#x2F;neocanable&#x2F;garlic&#x2F;blob&#x2F;72357ddbcffdb756416dd2fc1481f8c22be1c2c5&#x2F;src&#x2F;decompiler&#x2F;klass.c#L202">https:&#x2F;&#x2F;github.com&#x2F;neocanable&#x2F;garlic&#x2F;blob&#x2F;72357ddbcffdb75641...</a> )Sometimes it returns a static string like `g_str_int` and sometimes a newly heap-allocated string, such as returned by `class_type_array_name(g_str_int, depth)`.Callers have no way to properly release the memory allocated by this function.

cool, TIL!&gt; Examples of Vineflower&#x27;s output, compared to other decompilers, can be found on the wiki.[wiki is empty]:-&#x2F;

<a href="https:&#x2F;&#x2F;github.com&#x2F;Vineflower&#x2F;vineflower">https:&#x2F;&#x2F;github.com&#x2F;Vineflower&#x2F;vineflower</a>

I don&#x27;t think it&#x27;s available in a standalone repo but it IS available as a standalone library, IntelliJ&#x27;s FernFlower decompiler is the gold standard <a href="https:&#x2F;&#x2F;github.com&#x2F;JetBrains&#x2F;intellij-community&#x2F;blob&#x2F;master&#x2F;plugins&#x2F;java-decompiler&#x2F;engine&#x2F;src&#x2F;org&#x2F;jetbrains&#x2F;java&#x2F;decompiler&#x2F;main&#x2F;Fernflower.java">https:&#x2F;&#x2F;github.com&#x2F;JetBrains&#x2F;intellij-community&#x2F;blob&#x2F;master&#x2F;...</a> <a href="https:&#x2F;&#x2F;www.jetbrains.com&#x2F;intellij-repository&#x2F;releases" rel="nofollow">https:&#x2F;&#x2F;www.jetbrains.com&#x2F;intellij-repository&#x2F;releases</a>I guess there&#x27;s some history there that I&#x27;m not familiar with because JBoss also has a FernFlower decompiler library <a href="https:&#x2F;&#x2F;mvnrepository.com&#x2F;artifact&#x2F;org.jboss.windup.decompiler&#x2F;decompiler-fernflower" rel="nofollow">https:&#x2F;&#x2F;mvnrepository.com&#x2F;artifact&#x2F;org.jboss.windup.decompil...</a>

Jikes also gave massively better error messages than the official Java compiler, from what I remember, and it certainly ran a lot faster on the Amiga (<a href="https:&#x2F;&#x2F;aminet.net&#x2F;package&#x2F;dev&#x2F;lang&#x2F;jikes" rel="nofollow">https:&#x2F;&#x2F;aminet.net&#x2F;package&#x2F;dev&#x2F;lang&#x2F;jikes</a>) than trying to run javac via Kaffe (<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Kaffe" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Kaffe</a>) did.

Certainly not everything on Jikes, given that it was one of the first bootstraped Java toolchains.<a href="https:&#x2F;&#x2F;www.jikesrvm.org&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.jikesrvm.org&#x2F;</a>

The &quot;jikes&quot; compiler from IBM &lt;<a href="https:&#x2F;&#x2F;github.com&#x2F;daveshields&#x2F;jikespg">https:&#x2F;&#x2F;github.com&#x2F;daveshields&#x2F;jikespg</a>&gt; was written in C++ and was for the longest time screaming fast. It also had its own parser generator lpg which was fun to play with, if you&#x27;re into those things &lt;<a href="https:&#x2F;&#x2F;github.com&#x2F;daveshields&#x2F;jikespg">https:&#x2F;&#x2F;github.com&#x2F;daveshields&#x2F;jikespg</a>&gt;It seems someone liked it and made a &quot;v2&quot; along with LSP support <a href="https:&#x2F;&#x2F;github.com&#x2F;A-LPG&#x2F;LPG2#lpg2">https:&#x2F;&#x2F;github.com&#x2F;A-LPG&#x2F;LPG2#lpg2</a>

&gt; 10 times faster than that of JavaI was hoping that these days&#x27; Java would be &quot;almost&quot; as fast C&#x2F;C++. Oh well.

This has been my life experience with things written in C&#x2F;C++, so speed doesn&#x27;t matter. Or, I guess from an alternative perspective, it ran very fast, but exited very fast, too :-D<pre><code> $ .&#x2F;objdir&#x2F;garlic $the_jar_file -o out-dir -t $(nproc)
 Progress : 85 (1024)Segmentation fault: 11</code></pre>

I am writing the part of decompiling dex and apk. The current speed is about 10 times faster than that of Java, and it takes up less resources than Java. And the compiled binary is smaller, only about 300k. Thank you for your attention.

The readme shows support for dumping dex files. Edit: missed that it has a comment that stays &quot;unsupport for now&quot; but at least it looks like something planned

It is processes inner classes recursively. First read all entry from jar, and analyze the relationships between classes. Then do some decompile job.

Very cool project! Love the idea of a Java decompiler written in C — the speed must be great.Any plan to support `.dex` in the future? Also curious how you handle inner classes inside JARs.

Is there a good GUI for this a la jadx-gui that isn&#x27;t an entire IDE?

Things may have changed, but my impression as of several years ago was that JD-GUI was far, far behind the state of the art (Fernflower, aka the built-in IntelliJ decompiler) in terms of correctness, re-sugaring, support for modern Java features, and so on. Fernflower is open source as part of IntelliJ: <a href="https:&#x2F;&#x2F;github.com&#x2F;fesh0r&#x2F;fernflower">https:&#x2F;&#x2F;github.com&#x2F;fesh0r&#x2F;fernflower</a>

Nice job! I don&#x27;t know whether you know <a href="https:&#x2F;&#x2F;github.com&#x2F;java-decompiler&#x2F;jd-gui">https:&#x2F;&#x2F;github.com&#x2F;java-decompiler&#x2F;jd-gui</a> or not, but in case you haven&#x27;t seen it before, maybe you could use it as a reference, since it&#x27;s written in Java, for extra fun with your adventure?

How does the output compare to <a href="https:&#x2F;&#x2F;www.decompiler.com&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.decompiler.com&#x2F;</a> in terms of correctness?

I think that sort of ratio is the sweet spot for learning. I&#x27;ve been writing an 8086 simulator in C++ and using an LLM for answering specific technical questions I come up with has drastically sped up my progress without it actually doing the work for me.

Wow, impressive. A project of the scale and depth.

90% by hand, 10% AI. I do this for fun and to learn about jvm.

To some people the process leading to a finished project is the most interesting thing about posts like these.

Irrelevant to me. People would never ask whether someone has created something looking at SO or not. If the thing works as advertised, good for them!

A great question to ask. We&#x27;re in the middle of learning where AI can and can&#x27;t be effective. Knowing where and how it&#x27;s being used is quite useful.

By hand or with AI? Fascinating. So much work! What was your motivation for this?

Of course it can be done! It wouldn&#x27;t be as general purpose as the Java decompiler in C because the C decompiler would have to know about the CPU architecture of the executable code (just as the Java decompiler has to know about JVM opcodes).

<a href="https:&#x2F;&#x2F;github.com&#x2F;NationalSecurityAgency&#x2F;ghidra&#x2F;blob&#x2F;Ghidra_11.3.2_build&#x2F;Ghidra&#x2F;Processors&#x2F;x86&#x2F;src&#x2F;main&#x2F;java&#x2F;ghidra&#x2F;app&#x2F;plugin&#x2F;core&#x2F;analysis&#x2F;X86Analyzer.java">https:&#x2F;&#x2F;github.com&#x2F;NationalSecurityAgency&#x2F;ghidra&#x2F;blob&#x2F;Ghidra...</a> (Apache 2)

Can you also write a C decompiler in pure Java language?

I moved from C++ to C and I am more productive. I also think this &quot;no seat belts&quot; meme is exaggerated, as there are plenty of tools and strategies to make C fairly safe to use. (it is true though that many people do not put the seat belts on).

I can&#x27;t recall anything in that sense regarding Modula-2 and Object Pascal, other than not bringing UNIX to the party.

In my experience, although many of the other programming languages do improve some things compared with C, they also make many things worse and avoid some of the benefits of C programming.

I cannot help but wonder why I would learn a whole new language before even beginning to start a new project when I already know C. Though, generally speaking, I tend to use C++ for new projects -- usually depending on what libraries I&#x27;m using, if the lib is in C I use C and if the lib is in C++ I use C++. The current thing I&#x27;m working on is intended as a Python extension module and Python is written in C so...And, yes, I know it&#x27;s trivial to interface the Python C-API with C++ and quite often better as the &#x27;object model&#x27; is very similar but the underlying concept I wanted to explore (guaranteed tailcalls) isn&#x27;t possible in C++ from what I can tell.

Yes, yes I&#x27;m sure. I like using C sometimes.

This is the best question for me. Writing these codes in C language is the best way to learn the file structure of jvm&#x2F;dalvik&#x2F;pe. This process makes me like C language more. For me, I think it is simple and pure, which is enough.

Or riding a motorcycle.But stupid real-world analogies are stupid.

ejector seats in C car?goto eject;
...more code we are going to ignore, it could be important but nah, ignore it, what could be happen?...eject:
 up_through_the_roof();:D

i only write in C. if id build a car it wouldnt have seatbelts. boring, put in ejector seats! not safe? no problem for C :).

Rust has the same low-level memory model as C without the footguns.

We need people who can (and do) write in C, assembly, and all these low-level languages. Otherwise, software will just get slower and slower.

When debugging complex projects, the C language is more flexible and convenient to view data in memory.

It&#x27;s thanks to people like you that rust is not more widely used, you actively make people avoid the rust cummunity because they will think everybody i like you!

I cannot help but wonder why starting a new project in C in 2025. It’s like driving a car with no seat belts. You sure you want to do that?

Show HN: I wrote a Java decompiler in pure C language