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

[Dmitri Gribenko]

Hi William,

On Tue, Dec 8, 2015 at 8:00 PM, William Dillon via swift-dev <
swift-dev at swift.org> wrote:

> 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 and here’s my Github fork if you want
> to play along at home: 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’.
>

'long' and 'long int' are the same type.

Try preprocessing the following program with 'clang -E' and check how the
type is defined:

#include <unistd.h>
#include <sys/types.h>


> 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.
>
>
Use #if:

#if defined(__linux__) && defined(__arm__)
...
#else
...
#endif

To find the specific macro names to check for, dump the predefines buffer
and find an appropriate one (although I think __linux__ and __arm__ are
correct):

echo "" | clang -x c++ -std=c++11 - -dM -E

Dmitri

-- 
main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
(j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/
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