Re: different linker parameters from similar Makefiles when building MSVC DLLs in cygwin (with erlang wrappers)

[Peter Rosin]

Den 2011-06-28 13:47 skrev Dave Cottlehuber:
> Hi libtoolers,
> 
> I am building 2 Win32 DLLs to be loaded into the erlang runtime VM as NIFs,
> based on snappy (mixed C & C++) and ejson/yajl (in C), all part of porting
> latest CouchDB trunk to Windows - config is at [8].
> 
> They use a similar Makefile.am [2],[3] and share configure.ac [1], but during
> compile & linking ejson succeeds [7] and snappy doesn't [6], despite the
> Makefiles being almost identical.
> 
> There are 2 errors reported;
> - output filename is specified twice & therefore fails
> 
>         LINK : fatal error LNK1149: output filename matches input
> filename 'C:\cygwin\relax\git_couch\src\snappy\.libs\snappy_nif.dll'
> 
> - libtool adds unwanted flags, instead of -DLL (per working build)
> 
>         LINK : warning LNK4044: unrecognized option '/shared'; ignored
>         LINK : warning LNK4044: unrecognized option '/nostdlib'; ignored
>         LINK : warning LNK4044: unrecognized option
> '/-enable-auto-image-base'; ignored
>         LINK : warning LNK4044: unrecognized option '/Xlinker'; ignored
>         LINK : warning LNK4044: unrecognized option '/-out-implib'; ignored
>         LINK : warning LNK4044: unrecognized option '/Xlinker'; ignored
> 
> Only the final link phases differ materially in the parameters passed. If [7] 
> is
> manually run with these changes, bringing it into line with [6], it works:
> 
>     - remove '-Xlinker --out-implib -Xlinker \$lib'
>     - swap '-shared -nostdlib' ' for '-dll'
> 
> When libtool is hacked up [4], I can get a cleanish link [5] but this clearly
> isn't the Right Thing To Do.
> 
> What do I need to change, to ensure libtool passes the linker the same options
> in both DLLs? What am I missing?
> 
> Finally, given we are using these makefiles/configure.ac on multiple platforms
> have you got any other suggestions to improve things?

Lots of questions. Here's a a couple of my questions...
What is cc.sh? Some kind of wrapper I suppose? Have you checked how the
libtool testsuite fares when run with that wrapper?
How did you configure the different packages?
Have you tried to build with MinGW?

In my experience, attempting to write ad-hoc wrappers that makes MSVC look
like gcc is not what works best. I dearly recommend that you ditch the
cc.sh wrapper and instead use the compile wrapper from automake and trigger
its use with AM_PROG_CC_C_O in your configure.ac. Unfortunately you need
to get copies of a recent version the compile wrapper from the Automake git
repository (master branch, in the lib subdir). Also grab the ar-lib wrapper
script from there. Then configure your packages along these lines:

.../configure CC="cl -nologo" CFLAGS=-MD CXX="cl -nologo" CXXFLAGS=-MD LD=link 
AR=/path/to/ar-lib NM="dumpbin -symbols" STRIP=: RANLIB=:

Cheers,
Peter