Date: Mon, 7 Jan 2013 09:36:38 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-arch@freebsd.org Cc: freebsd-toolchain@freebsd.org, Nathan Whitehorn <nwhitehorn@freebsd.org> Subject: Re: LLVM Image Activator Message-ID: <201301070936.39052.jhb@freebsd.org> In-Reply-To: <50E9BC2D.7000302@freebsd.org> References: <50E9BC2D.7000302@freebsd.org>
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On Sunday, January 06, 2013 01:02:21 PM Nathan Whitehorn wrote: > Having LLVM/clang in the base system lets us do some interesting things > that we couldn't do with GCC. One is that LLVM ships with a JIT for LLVM > IR as well as components of a toolchain for it (this is what Google's > pNACL uses) and that you can end up producing binary files that are in > IR instead of native code. The IR isn't really cross-platform, but does > let you do CPU-specific optimizations when executed by the JIT, etc. > > The attached patch causes the LLVM JIT (lli) to be built by default > (adding ~20 seconds to buildworld on my five-year-old laptop) and adds a > kernel image activator that invokes it when passed LLVM bitcode files. > It's not completely finished (see the XXX comment in the middle), but it > does work, as follows: > > $ clang -emit-llvm -c -o hw.ll hw.c > $ file hw.ll > hw.ll: LLVM bitcode > $ lli hw.ll > Hello world! > $ chmod a+x hw.ll > $ ./hw.ll > Hello world! > $ > > Is there any interest in having features like this? It seems like this > could provides some interesting possibilities for us and nice > integration from having imported clang into base. > -Nathan This sounds neat indeed. Does the IR format provide any sort of notation for encoding the path to the interpreter (similar to ELF)? If not, you might want to at least make the path to 'lli' be configurable via a tunable and/or sysctl (e.g. if using a newer version of clang in /usr/local). -- John Baldwin
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