[swift-dev] [SR-40] Port Swift to Arm progress / question

[William Dillon]

Hi all,

I’ve been working on trying to get Swift to compile on ARMv7 (armv7l specifically, not sure if other variants will work as well).  I’ve gotten pretty far, but I ran a cross an issue that has me a little confused.  For convenience, here’s the bug that has some of my messages in the comments: https://bugs.swift.org/browse/SR-40 <https://bugs.swift.org/browse/SR-40> and here’s my Github fork if you want to play along at home: https://github.com/hpux735/swift <https://github.com/hpux735/swift>  By the way, I’m compiling on an Nvidia tegra TK2 development board with 2GB of ram and a 25GB swapfile on an external SSD.  This brings native compile times down to reasonable levels.  I was compiling on the BeagleBone Black formerly, and that was painful (like over a day for LLVM).

So far, cmark and llvm compile just fine (no surprise there), and swift gets pretty far along.  The weird issue, which will certainly expose my weakness in C++ and large build systems, is that the swift_ssize_t doesn’t match ssize_t.  

[6/61] Building CXX object stdlib/public/stubs/CMakeFiles/swiftStdlibStubs-linux-armv7.dir/Stubs.cpp.o
FAILED: /usr/bin/clang++   -DGTEST_HAS_RTTI=0 -D_DEBUG -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -fno-stack-protector -fPIC -fvisibility-inlines-hidden -Wall -W -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wcovered-switch-default -Wnon-virtual-dtor -Werror=date-time -std=c++11 -fcolor-diagnostics -ffunction-sections -fdata-sections -Wdocumentation -Wimplicit-fallthrough -Wunreachable-code -Woverloaded-virtual -O3  -Istdlib/public/stubs -I/home/wdillon/swift/stdlib/public/stubs -I/home/wdillon/swift/include -Iinclude -I/home/wdillon/build/Ninja-ReleaseAssert/llvm-linux-armv7/include -I/home/wdillon/llvm/include -I/home/wdillon/build/Ninja-ReleaseAssert/llvm-linux-armv7/tools/clang/include -I/home/wdillon/llvm/tools/clang/include -I/home/wdillon/cmark/src -I/home/wdillon/build/Ninja-ReleaseAssert/cmark-linux-armv7/src    -UNDEBUG  -fno-exceptions -fno-rtti  -Wglobal-constructors -Wexit-time-destructors -target arm-unknown-linux-gnueabihf -isysroot / -O2 -g0 -UNDEBUG -MMD -MT stdlib/public/stubs/CMakeFiles/swiftStdlibStubs-linux-armv7.dir/LibcShims.cpp.o -MF "stdlib/public/stubs/CMakeFiles/swiftStdlibStubs-linux-armv7.dir/LibcShims.cpp.o.d" -o stdlib/public/stubs/CMakeFiles/swiftStdlibStubs-linux-armv7.dir/LibcShims.cpp.o -c /home/wdillon/swift/stdlib/public/stubs/LibcShims.cpp
/home/wdillon/swift/stdlib/public/stubs/LibcShims.cpp:24:1: error: static_assert failed "__swift_ssize_t is wrong"
static_assert(std::is_same<ssize_t, swift::__swift_ssize_t>::value,
^             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

Now, the sizes match (4 bytes each), but the std::is_same() function says no.  I grep’d the clang codebase for the definition of ssize_t, and it seems like it’s a ‘long’ whereas the swift_ssize_t is a 'long int’.  I looked into the LibcShims a bit, and the expectation is that the definition in the header is not universally correct, and will be checked:

// This declaration is not universally correct.  We verify its correctness for
// the current platform in the runtime code.
typedef long int __swift_ssize_t;

And it is thusly (in LibcShims.cpp):

static_assert(std::is_same<ssize_t, swift::__swift_ssize_t>::value, "__swift_ssize_t is wrong”);

What’s less clear is the mechanism with which I am to change this definition in a way that doesn’t mess-up other platforms.

Any thoughts and ideas are welcome!
Cheers,
- Will
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