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diff --git a/content/posts/2007-10-15-llvm-is-a-baby-killer.html b/content/posts/2007-10-15-llvm-is-a-baby-killer.html new file mode 100644 index 0000000..0bd1623 --- /dev/null +++ b/content/posts/2007-10-15-llvm-is-a-baby-killer.html @@ -0,0 +1,57 @@ +--- +date: "2007-10-15T05:38:29Z" +title: LLVM is a Baby Killer +--- + +<img src='http://pablotron.org/gallery/misc/baby_kill-small.png' + width='200' height='199' align='right'/> +<p> +I've spent some time sifting through the documentation for <a href="http://llvm.org/">LLVM</a>, and +I'm both impressed and horrified. I'm not sure I've ever seen so much +documentation about something that looks really cool that I'm not +interested in. I've been reading the <a href="http://en.wikipedia.org/wiki/Compilers:_Principles%2C_Techniques%2C_and_Tools">dragon book</a> and <a href='http://www.amazon.com/Advanced-Compiler-Design-Implementation-Muchnick/dp/1558603204'>Advanced Compiler Design and Implementation</a>, and I <em>wanted</em> to use LLVM to generate a simple +runtime <acronym title='Just in Time (compiler)'>JIT</acronym> compiler, but I can't seem to find the necessary +documentation. </p> + +<p>I see plenty of documentation on the IR, the various command-line tools, +and just about everything else LLVM-related except for a straightforward +tutorial that explains how to </p> + +<ol> +<li>blast either opcodes or IR at the LLVM <acronym title='Application Programming Interface'>API</acronym>, and </li> +<li>have LLVM either emit an ELF/blob/whatever or execute the result. </li> +</ol> + +<p>I did manage to find a couple of examples that give me half of what I +want. The source code ships with a sample <a href="http://en.wikipedia.org/wiki/Brainfuck">Brainfuck</a> compiler which +reads an input bf file and emits LLVM IR. There are a couple more +examples that show how to construct a basic JIT, then create some +functions that do frustratingly simple things like calculate Fibonacci +numbers or add two integers together, but nothing that's too much more +detailed than that.</p> + +<p>Oh, did I mention that the online API documentation is broken?</p> + +<p>A bit of googling turned up libjit, which is almost exactly what I want. +It's got a simple C API (instead of the nightmarishly bloated C++ +monstrosity that is the LLVM API), a simple build and link system, and +<a href="http://maybe.dotgnu.info:8000/~krokas/books/libJIT/libjit_toc.html">simple, straightforward and complete documentation</a>. In +short, it's everything that I want. </p> + +<p>It's also GPL-licensed, which makes it almost completely unusable. I +found <a href="http://lists.cs.uiuc.edu/pipermail/llvmdev/2006-April/005581.html">this 2006 email exchange</a> comparing libgit and LLVM. The +author, who apparently works on libgcj, mentions all of my problems with +LLVM (sans the anti-C++ bias). </p> + +<p>My other crazy idea was to generate C as an IR and blast it at +<a href="http://fabrice.bellard.free.fr/tcc/">libtcc</a>, but with my limited fiddling I couldn't get to do anything +other than segfault on me. Incidentally, the documentation for libtcc +is a single file and it's still better than what's available for LLVM.</p> + +<p>So here's my question: Is there a decent book or tutorial that walks +through the LLVM API? I've Googled to the end of the earth and back, +I've seen the <a href="http://llvm.org/docs/Stacker.html">Stacker</a> documentation, and I've read through +<em>everything</em> in the LLVM documentation section, and none of it was +what I'm looking for. I'm open to suggestions...</p> + + |