117 lines
4.6 KiB
Markdown
117 lines
4.6 KiB
Markdown
LLVM MinGW
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==========
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This is a recipe for reproducibly building a
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[LLVM](https://llvm.org)/[Clang](https://clang.llvm.org/)/[LLD](https://lld.llvm.org/)
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based mingw-w64 toolchain.
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Benefits of a LLVM based MinGW toolchain are:
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- Support for targeting ARM/ARM64 (while GCC obviously does support
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these architectures, it doesn't support Windows on ARM)
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- A single toolchain targeting all four architectures (i686, x86_64,
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armv7 and arm64) instead of separate compiler binaries for each
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architecture
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- Support for generating debug info in PDB format
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- Support for Address Sanitizer and Undefined Behaviour Sanitizer
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Clang on its own can also be used as compiler in the normal GNU binutils
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based environments though, so the main difference lies in replacing
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binutils with LLVM based tools.
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The toolchain can be reproducibly built into a Docker image, or be
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built and installed in the host environment (currently only tested
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on Linux and macOS).
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To build and install all components, just do:
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./build-all.sh <target-dir>
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To reduce the size of the installation, removing some files that
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aren't necessary after building, run:
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./strip-llvm.sh <target-dir>
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To build a Docker image with the toolchain, run:
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docker build .
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Individual components of the toolchain can be (re)built by running
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the standalone shellscripts listed within `build-all.sh`. However, if
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the source already is checked out, no effort is made to check out a
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different version (if the build scripts have been updated to prefer
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a different version) - and likewise, if configure flags in the build-\*.sh
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scripts have changed, you might need to wipe the build directory under
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each project for the new configure options to be taken into use.
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Prebuilt docker linux images containing llvm-mingw are available from
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[Docker Hub](https://hub.docker.com/r/mstorsjo/llvm-mingw/), and
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prebuilt toolchains (both for use as cross compiler from linux, and
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for use on windows) are available for download on GitHub. The toolchains
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for windows come in 4 versions, one for each of the 4 supported
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architectures, but each one of them can target all 4 architectures.
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Status
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------
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The toolchain currently does support both C and C++, including support
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for exception handling.
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It is in practice new and hasn't been tested with quite as many projects
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as the regular GCC/binutils based toolchains yet. You might run into issues
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building non-trivial projects.
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Known issues
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------------
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LLD, the LLVM linker, is what causes most of the major differences to the
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normal GCC/binutils based MinGW.
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- The windres replacement, llvm-rc, isn't very mature and doesn't support
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everything that GNU windres does.
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- The toolchain defaults to using the Universal CRT (which is only available
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out of the box since Windows 10, but can be installed on Vista or newer)
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and defaults to targeting Vista. These defaults can be changed in
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`build-mingw-w64.sh` though.
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- The toolchain uses Windows native TLS support, which doesn't work properly
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until Windows Vista. This has no effect on code not using thread local
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variables.
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- The runtime libraries libunwind, libcxxabi and libcxx also assume that the
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target is Vista or newer.
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- Address Sanitizer doesn't produce working backtraces for i686. Address
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Sanitizer requires using a PDB file for symbolizing the error location and
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backtraces.
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- The sanitizers are only supported on x86.
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Additionally, one may run into other minor differences between GCC and clang.
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PDB support
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-----------
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LLVM does [support](http://blog.llvm.org/2017/08/llvm-on-windows-now-supports-pdb-debug.html)
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generating debug info in the PDB format. Since GNU binutils based mingw
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environments don't support this, there's no predecent for what command
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line parameters to use for this, and llvm-mingw produces debug info in
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DWARF format by default.
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To produce debug info in PDB format, you currently need to do the following
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changes:
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- Add `-gcodeview` to the compilation commands (e.g. in
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`wrappers/clang-target-wrapper.sh`), together with using `-g` as usual to
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enable debug info in general.
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- Add `-Wl,-pdb=` to linking commands. This creates a PDB file at the same
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location as the output EXE/DLL, but with a PDB extension. (By passing
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`-Wl,-pdb=module.pdb` or `-Wl,-pdb,module.pdb` one can explicitly specify
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the name of the output PDB file.)
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Even though LLVM supports this, there are a few caveats with using it when
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building in MinGW mode:
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- Microsoft debuggers might have assumptions about the C++ ABI used, which
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doesn't hold up with the Itanium ABI used in MinGW.
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- This is unimplemented for the armv7 target, and while implemented for aarch64,
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it doesn't seem to work properly there yet.
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