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build-mingw-w64.sh: Document my findings
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Andrew Eikum
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commit
3454fff8d3
@ -2,10 +2,127 @@
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set -e
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# The Story So Far
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#
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# We need two cross-compilers to build Proton. These each have to run in the
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# Steam runtimes, each of which only supports 32- or 64-bit programs. Our build
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# VM is a 64-bit Linux machine. So our platform configurations are:
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#
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# 64-bit cross-compiler:
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# Build (where the compiler is built): 64-bit linux (our VM)
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# Host (where the compiler is run): 64-bit linux (64-bit Steam runtime)
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# Target (what the compiler outputs): 64-bit win32 (PE files to be run)
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#
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# 32-bit cross-compiler:
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# Build (where the compiler is built): 64-bit linux (our VM)
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# Host (where the compiler is run): 32-bit linux (32-bit Steam runtime)
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# Target (what the compiler outputs): 32-bit win32 (PE files to be run)
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#
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# The former is a pretty standard cross-compiler setup.
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#
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# gcc calls the latter, where all of the platforms are different, a "Canadian"
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# build. See "The GNU configure and build system" by Ian Lance Taylor, section
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# "Canadian Cross", available here:
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# https://www.airs.com/ian/configure/configure_6.html
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#
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# This turned out to be quite difficult, possibly due to the added complexity of
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# mingw-w64. I'm documenting the problems I had and how I solved/worked around
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# them here, to hopefully save myself or someone else some heartburn in the
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# future. If you are a compiler expert and find yourself shaking your head at
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# this poor fool, I welcome your assistance improving this.
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#
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# Canadian builds require the build machine to already have a cross-compiler for
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# the Target platform available on the Build machine. Without this, the gcc build
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# will fail with:
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#
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# i686-w64-mingw32-gcc -dumpspecs > tmp-specs
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# /bin/bash: i686-w64-mingw32-gcc: command not found
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#
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# We are building both C and C++ lang support, so we need both gcc and g++
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# cross-compilers available. With the Build->Target cross-compilers installed,
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# we can now build gcc, and use that to build mingw-w64. After that, we need to
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# build gcc's libraries, like libgcc and libstdc++v3, against those mingw-w64
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# libraries. However, the libatomic and/or libgomp builds will fail with:
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#
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# checking for suffix of object files...
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# configure: error: in `/home/vagrant/mingw/build-i686-w64-mingw32/gcc/i686-w64-mingw32/libatomic':
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# configure: error: C compiler cannot create executables
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# See `config.log' for more details
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#
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# checking for suffix of object files...
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# configure: error: in `/home/vagrant/mingw/build-i686-w64-mingw32/gcc/i686-w64-mingw32/libgomp':
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# configure: error: C compiler cannot create executables
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# See `config.log' for more details
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#
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# Digging into config.log shows it can't find libgcc:
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#
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# configure:3722: checking whether the C compiler works
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# configure:3744: i686-w64-mingw32-gcc -L/home/vagrant/mingw/output/i686-w64-mingw32/lib -L/home/vagrant/mingw/output/mingw/lib -isystem /home/vagrant/mingw/output/i686-w64-mingw32/include -isystem /home/vagrant/mingw/output/mingw/include -g -O2 conftest.c >&5
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# /home/vagrant/mingw/output/lib/gcc/i686-w64-mingw32/9.2.0/../../../../i686-w64-mingw32/bin/ld: cannot find -lgcc
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# /home/vagrant/mingw/output/lib/gcc/i686-w64-mingw32/9.2.0/../../../../i686-w64-mingw32/bin/ld: cannot find -lgcc_eh
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# /home/vagrant/mingw/output/lib/gcc/i686-w64-mingw32/9.2.0/../../../../i686-w64-mingw32/bin/ld: cannot find -lgcc
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# /home/vagrant/mingw/output/lib/gcc/i686-w64-mingw32/9.2.0/../../../../i686-w64-mingw32/bin/ld: cannot find -lgcc_eh
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# collect2: error: ld returned 1 exit status
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#
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# I don't know what causes this (maybe Canadian builds don't like being split up
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# like this?). However, installing libgcc explicitly first will work around it.
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# After installing libgcc explicitly, we can then build the rest of gcc's
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# libraries. That was all the easy (ha!) stuff. At this point, you will have a
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# cross-compiler that will build Proton.
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#
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# However, there's a sneaky problem. For some reason the libstdc++v3 build system
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# requires libstdc++ to be available to detect C-lang functions(?!?). It will
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# still build without those C functions, but it may have far worse performance
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# (see Proton github issue #3198). You can detect this situation by examining the
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# config.log output for libstdc++v3 after your build completes:
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#
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# configure:16811: checking for gettimeofday
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# configure:16827: checking sys/time.h usability
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# configure:16827: i686-w64-mingw32-c++ -L/home/vagrant/mingw/output/i686-w64-mingw32/lib -L/home/vagrant/mingw/output/mingw/lib -isystem /home/vagrant/mingw/output/i686-w64-mingw32/include -isystem /home/vagrant/mingw/output/mingw/include -c -g -O2 -fno-exceptions conftest.cpp >&5
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# configure:16827: $? = 0
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# configure:16827: result: yes
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# configure:16827: checking sys/time.h presence
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# configure:16827: i686-w64-mingw32-c++ -L/home/vagrant/mingw/output/i686-w64-mingw32/lib -L/home/vagrant/mingw/output/mingw/lib -isystem /home/vagrant/mingw/output/i686-w64-mingw32/include -isystem /home/vagrant/mingw/output/mingw/include -E conftest.cpp
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# configure:16827: $? = 0
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# configure:16827: result: yes
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# configure:16827: checking for sys/time.h
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# configure:16827: result: yes
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# configure:16840: checking for gettimeofday
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# configure:16875: i686-w64-mingw32-c++ -L/home/vagrant/mingw/output/i686-w64-mingw32/lib -L/home/vagrant/mingw/output/mingw/lib -isystem /home/vagrant/mingw/output/i686-w64-mingw32/include -isystem /home/vagrant/mingw/output/mingw/include -o conftest.exe -g -O2 -fno-exceptions conftest.cpp >&5
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# /home/vagrant/mingw/output/lib/gcc/i686-w64-mingw32/9.2.0/../../../../i686-w64-mingw32/bin/ld: cannot find -lstdc++
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# collect2: error: ld returned 1 exit status
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#
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# But that error doesn't kill configure, and it happily continues with this in
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# config.h:
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#
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# /* #undef _GLIBCXX_USE_GETTIMEOFDAY */
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#
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# This triggers the bad codepath in libstdc++v3 that caused the performance
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# problem mentioned above, and is clearly wrong anyway, as gettimeofday is
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# definitely available. Yes, this was a huge pain to puzzle out. I "solved" this
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# by letting the libstdc++v3 build continue, then re-running the build after
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# installing it, so now it will find libstdc++ and so correctly detect the C-lang
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# function that has nothing at all to do with libstdc++. Argh.
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#
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# After all that, we finally have a functioning set of cross-compilers. Most of
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# the configuration parameters used here are taken from the Arch Linux mingw-w64
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# PKGBUILDs, as those were written by someone with more knowledge than me, and
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# have had a lot of testing. We make one tweak to the gcc configuration, which is
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# to disable SJLJ exceptions and enable DWARF2 debug symbols. The former
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# apparently helps with performance on 32-bit, and the latter puts debug symbols
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# in a format that more Linux tooling can read.
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#
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# Side note, the Arch Linux PKGBUILDs work very differently from how this script
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# works. While working on this, I tried to adapt the PKGBUILDs' process here
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# (e.g. build a bootstrap C-lang compiler, use that to build mingw-w64, then
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# rebuild gcc against the mingw-w64 CRT with C++-lang support), but I ran into a
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# ton of problems, possibly caused by the Canadian-ness of the build, and
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# eventually ran out of ideas for working around them.
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if [ -z "$1" ]; then
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echo "Makes a local build of mingw-w64 in this directory and installs it to the given path."
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echo ""
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echo "Note: Requires a system mingw-w64 to be present already, for us to bootstrap with."
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echo "Note: Requires a system mingw-w64 compiler to be present already on your build machine, for us to bootstrap with."
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echo ""
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echo "usage:"
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echo -e "\t$0 <installation path e.g. \$HOME/.local>"
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@ -175,7 +292,7 @@ function build_arch {
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pushd gcc/
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#next step requires libgcc in default library location, but
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#"canadian" build doesn't handle that, so install it explicitly
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#"canadian" build doesn't handle that(?), so install it explicitly
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PATH=$NEWPATH make configure-target-libgcc
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PATH=$NEWPATH make -C $WIN32_TARGET_ARCH/libgcc $JOBS
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PATH=$NEWPATH make -C $WIN32_TARGET_ARCH/libgcc $JOBS install
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