Building DLLs

[mikejohnstn]

Thanks for all your work helping to bring Swift to Windows.

Do you plan to support building a DLL instead of an executable? This would help a lot for those of us interested in using Swift to write cross-platform libraries.

[tinysun212]

Thanks for your suggestion.

That's very good feature to support building libraries to share.
I didn't have the building-libraries-plan yet.
Instead, I have the plan porting the Foundation module and the Dispatch module to MinGW-w64 Swift.
I'll take the building-libraries-plan after those portings since Foundation module is very important for cross-platform coding.

[mikejohnstn]

Agreed, porting Foundation and Dispatch will be great as well. Thanks for your efforts.

[gmondada]

Hi,
Thanks a lot for your amazing work.
Actually, do you know what is missing to generate a DLL containing swift code? The linker seems to know what a DLL is. You can generate one with:
swiftc hello.swift -o hello.dll -Xlinker -dll -Xlinker --export-all-symbols

Checking the DLL content with Microsoft dumpbin gives this:

$ /cygdrive/c/Program\ Files\ \(x86\)/Microsoft\ Visual\ Studio\ 14.0/VC/bin/dumpbin.exe /DEPENDENTS /EXPORTS hello.dll
Microsoft (R) COFF/PE Dumper Version 14.00.24213.1
Copyright (C) Microsoft Corporation.  All rights reserved.


Dump of file hello.dll

File Type: DLL

  Section contains the following exports for hello.dll

    00000000 characteristics
    5955224C time date stamp Thu Jun 29 16:52:44 2017
        0.00 version
           1 ordinal base
           6 number of functions
           6 number of names

    ordinal hint RVA      name

          1    0 00004036 __swift_reflection_version
          2    1 000016F0 get_number
          3    2 000015E0 hello
          4    3 000015B0 main
          5    4 000016E0 swift_rt_swift_release
          6    5 000016D0 swift_rt_swift_retain

  Image has the following dependencies:

    KERNEL32.dll
    msvcrt.dll
    libswiftSwiftOnoneSupport.dll
    libswiftCore.dll

  Summary

        1000 .CRT
        1000 .bss
        1000 .data
        3000 .debug_abbrev
        1000 .debug_aranges
        1000 .debug_frame
       49000 .debug_info
        3000 .debug_line
        3000 .debug_loc
        1000 .debug_ranges
        1000 .debug_str
        1000 .edata
        1000 .idata
        1000 .pdata
        1000 .rdata
        1000 .reloc
        1000 .swift1_autolink_entries
        1000 .swift_modhash
        2000 .text
        1000 .tls
        1000 .xdata

We see get_number and hello symbols corresponding to two functions I wrote in swift:

@_silgen_name("hello") public func hello() {
    print("hello world")
}
@_silgen_name("get_number") public func getNumber() -> Int32 {
    return 1234
}

However, linking the DLL to a program (msvcrt.dll based) makes that program crashing. Loading it with LoadLibrary() returns ERROR_DLL_INIT_FAILED.
I also tried to generate an EXE file which exports all symbols, with:
swiftc hello.swift -o hello.exe -Xlinker --export-all-symbols
and I was able to load the EXE file with LoadLibrary(), get the address of get_number() thanks to GetProcAddress() and call get_number() which returned 1234. Doing the same to call hello() results in a crash.
So, I think we miss the code that should initialise the swift environment or whatever needed to swift to run properly. Do you know how this should work?
I will probably try to call the DLL from a swift program. Maybe in this way the DLL runs in an environment that the main program has already set up. I think this is what happen with libswiftCore.dll which is a DLL written in swift, isn't it?

[WorikQCI]

Many years later: Can I compile my Swift code on Windows as a dynamic library (DLL)?

I wish to call it from programme written in a different language