LLVM Cross-Compiler: Difference between revisions
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EDIT: A more up-to-date version with Clang 3.4 is posted [http://exocortex.madfire.net/post/2013/05/23/compiling-llvm-trunk/ here]. |
EDIT: A more up-to-date version with Clang 3.4 is posted [http://exocortex.madfire.net/post/2013/05/23/compiling-llvm-trunk/ here]. |
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EDIT: A mostly working Clang cross-compiler is generated by [ |
EDIT: A mostly working Clang cross-compiler is generated by [https://github.com/berkus/metta/blob/develop/build_toolchain.sh this buildscript]. Dissect it to learn more. |
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TODO: move details to this page. |
TODO: move details to this page. |
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Disables standard library |
Disables standard library |
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==== -nostdinc ==== |
==== -nostdinc ==== |
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Makes sure the standard library |
Makes sure the standard library headers are not included. |
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==== -nostdinc++ ==== |
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Makes sure the standard C++ library headers are not included. This makes sense if you build a custom version of libc++ and want to avoid including system one. |
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== TODO == |
== TODO == |
Revision as of 10:56, 29 May 2013
Difficulty level |
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Advanced |
EDIT: A more up-to-date version with Clang 3.4 is posted here.
EDIT: A mostly working Clang cross-compiler is generated by this buildscript. Dissect it to learn more. TODO: move details to this page.
EDIT: EmbToolkit project recently added support to clang/llvm based cross compiler. TODO: Add note about how it works.
Introduction
About
Generally speaking, a cross-compiler is a compiler that runs on platform A (the host), but generates executables for platform B (the target). These two platforms may (but do not need to) differ in CPU, operating system, and/or executable format.
Clang (and llvm) are host cross compilers. They by default have the capability to cross compile, but also produce host binaries. See Usage
Requirements
- A host system with a working compiler.
- A bash shell or comparable environment. If you are not using a bash shell, you might have to modify some of the command lines below. If you have just installed the basic Cygwin package, you have to run the setup.exe again and install the following packages:
- GCC (even if you have something like MinGW installed)
- make
- binutils (a fairly recent version of binutils, try 2.21 or above if you get assembly compilation errors)
- subversion (if using svn build
- cmake
Building
Subversion Build (Possibly Unstable)
In bash, run
mkdir crossllvm
cd crossllvm
svn co http://llvm.org/svn/llvm-project/llvm/trunk llvm
cd llvm/tools
svn co http://llvm.org/svn/llvm-project/cfe/trunk clang
cd ../..
mkdir build
cd build
cmake ../llvm
make
Now you have got llvm built!
Debian
Open a terminal
sudo apt-get install clang
Note, you might have to disable host functionality. See Useful Flags
Usage
After building you will have a compiler able to output multiple output formats regardless of your current platform.
For example, for cross compiling to ARM, you can use
-march=armv7-a -mfloat-abi=soft -ccc-host-triple arm-elf
Since 3.1, it can be shortened to
-target armv7--eabi -mcpu=cortex-a9
Useful Flags
Some usefull flags for OS development.
-ffreestanding
Indicated that the file should be compiled for a freestanding enviroment (like a kernel), not a hosted (userspace), environment.
-fno-builtin
Disable special handling and optimizations of builtin functions like strlen and malloc.
-nostdlib
Disables standard library
-nostdinc
Makes sure the standard library headers are not included.
-nostdinc++
Makes sure the standard C++ library headers are not included. This makes sense if you build a custom version of libc++ and want to avoid including system one.
TODO
TODO: describe non-svn build from released tarballs.
TODO: integrate libc++ build instructions