Re: Using Gnat.Sockets in a Windows DLL

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2016-01-13 21:25, ahlan.marriott@gmail.com wrote:
> On Thursday, 26 November 2015 08:57:02 UTC+1, ah...@marriott.org  wrote:
>> We have windows programs and DLLs that use the Windows WinSock API directly.
>> In order to make this code target independent (at least for Linux & OSX) we thought we should convert the code to use Gnat.Sockets.
>> This is relatively trivial.
>> Or at least it is for programs.
>> When we try to convert our DLLs we run into a linker problem.
>> If all we do is a "with Gnat.Sockets" then using GprBuild produces lots of messages saying that various entry points could not be found.
>> See below.
>> I recognize many of them as being in WS2_32.dll - which GprBuild finds when we build our programs (its in Windows/System32)
>> Except that the names are not quite right so I suspect that this is the root cause of the problem.
>> Has anyone any idea why a build of a DLL should behave differently to a build of a program with respect to name mangling?
>>
>> Best wishes,
>> Ahlan
>> -----------
>>
>> gprbuild -d -PD:\Binary\Ada\tools\cal_dll\Cal_Dll.gpr -XWIN32ADA_BUILD=default -XLIBRARY_TYPE=static
>> gprlib.exe Cal_Dll.lexch
>> gnatbind -n -o b__Cal_Dll.adb -LCal_Dll -a -E D:\Binary\Ada\tools\cal_dll\objects\cal_dll_interface.ali
>> gcc.exe -c -x ada -gnatA -gnatws b__cal_dll.adb -o b__cal_dll.o ...
>> gcc.exe -shared -static-libgcc -o W:\product\windows\Cal_Dll.dll D:\Binary\Ada\tools\cal_dll\objects\cal_dll_interface.o ...
>> C:\gnatpro\7.3.1\lib\gcc\i686-pc-mingw32\4.9.3\/adalib/libgnat.a(g-socket.o):g-socket.adb:(.text+0x1b46): undefined reference to `gethostname@8'
>> C:\gnatpro\7.3.1\lib\gcc\i686-pc-mingw32\4.9.3\/adalib/libgnat.a(g-socket.o):g-socket.adb:(.text+0x1c9c): undefined reference to `getpeername@12'
>> C:\gnatpro\7.3.1\lib\gcc\i686-pc-mingw32\4.9.3\/adalib/libgnat.a(g-socket.o):g-socket.adb:(.text+0x2323): undefined reference to `getsockopt@20'
>> C:\gnatpro\7.3.1\lib\gcc\i686-pc-mingw32\4.9.3\/adalib/libgnat.a(g-socket.o):g-socket.adb:(.text+0x3518): undefined reference to `getsockopt@20'
>> C:\gnatpro\7.3.1\lib\gcc\i686-pc-mingw32\4.9.3\/adalib/libgnat.a(g-socthi.o):g-socthi.adb:(.text+0x1c): undefined reference to `WSASetLastError@4'
>> C:\gnatpro\7.3.1\lib\gcc\i686-pc-mingw32\4.9.3\/adalib/libgnat.a(g-socthi.o):g-socthi.adb:(.text+0x246): undefined reference to `WSASetLastError@4'
>> C:\gnatpro\7.3.1\lib\gcc\i686-pc-mingw32\4.9.3\/adalib/libgnat.a(g-socthi.o):g-socthi.adb:(.text+0x27f): undefined reference to `WSASetLastError@4'
>> C:\gnatpro\7.3.1\lib\gcc\i686-pc-mingw32\4.9.3\/adalib/libgnat.a(socket.o):socket.c:(.text+0x109): undefined reference to `_imp__getservbyname@8'
>> C:\gnatpro\7.3.1\lib\gcc\i686-pc-mingw32\4.9.3\/adalib/libgnat.a(socket.o):socket.c:(.text+0x159): undefined reference to `_imp__getservbyport@8'
>> C:\gnatpro\7.3.1\lib\gcc\i686-pc-mingw32\4.9.3\/adalib/libgnat.a(socket.o):socket.c:(.text+0x2a4): undefined reference to `__WSAFDIsSet@8'
>> C:\gnatpro\7.3.1\lib\gcc\i686-pc-mingw32\4.9.3\/adalib/libgnat.a(socket.o):socket.c:(.text+0x34c): undefined reference to `_imp__ioctlsocket@12'
>> C:\gnatpro\7.3.1\lib\gcc\i686-pc-mingw32\4.9.3\/adalib/libgnat.a(socket.o):socket.c:(.text+0x3b4): undefined reference to `_imp__WSAStringToAddressA@20'
>> collect2.exe: error: ld returned 1 exit status
>> gprlib: c:\gnatpro\7.3.1\bin\gcc execution error
>> gprbuild: could not build library for project cal_dll
>> [2015-11-26 08:36:34] process exited with status 4, 100% (36/36), elapsed time: 01.67s
>
> Dear all,
>
> It seems that this is an known problem.
> At least to AdaCore.
> They document it as KP-22-O331-001
> The problem is fixed in GprBuild v2.2.2 that is part of Gnat Pro 7.3.2
> Otherwise the workaround is not to produce an encapsulated DLL but
> to  produce a standard DLL and link in the static version of the Gnat
> runtime using Library_options.
> A standard DLL will link WS2_32 and linking in the static runtime will produce a standalone DLL.

I built the latest grpbuild from Git sources (not easy under Windows). 
The problem with encapsulated library projects persists.

Presently I believe it is related to the order in which libraries 
wsock32 and ws2_32 appear in the linker's command like. From what I read 
researching the issue, for some mysterious reasons, -lws2_32 -lwsock32 
must appear *before* -shared -static-libgcc. So the linker line must 
look like:

gcc.exe -lws2_32 -lwsock32 -shared -static-libgcc -o W:\product...

There is "Leading_Library_Option" project attribute, but it is no help 
because it does not bring its content right after gcc.exe.

Any ideas how to do it otherwise?

For example, a very crude way would to write an application 
my_gcc_wrapper that calls gcc with -lws2_32 -lwsock32 preceding all 
other switches and replace

package Linker is
    for Driver ("Ada") use "my_gcc_wrapper.exe";
end Linker;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de