Martin Storsjö
af4e0b0021
libwinstorecompat now provides a reimplementation of EnumProcessModules, making libunwind compatible with WinRT.
108 lines
4.1 KiB
Markdown
108 lines
4.1 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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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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This is similar to https://github.com/martell/mingw-w64-clang, with
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the exact same goal but with a slightly different mechanism for
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building it, allowing a full from-scratch build of all components
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in one command.
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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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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 quite new and immature and haven't been proven with a
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large number of projects yet though. You will probably 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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- LLD doesn't support using import libraries created by GNU tools.
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- LLD doesn't automatically fix up use of data symbols from DLLs without
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the dllimport attributes.
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- The C++ libraries ([libcxxabi](http://libcxxabi.llvm.org/), [libcxx](http://libcxx.llvm.org/)) can only be linked statically
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at the moment.
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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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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,module.pdb` to linking commands.
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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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- Call stack unwinding on x86_64 requires the binaries to be built with SEH.
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This toolchain currently uses DWARF for exception unwinding instead of SEH,
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since libcxxabi doesn't support unwinding using SEH. Thus currently, on
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x86_64, one can only inspect the actual crashed function, not callers further
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up. On i686, things seem to work fine though.
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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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