> On 2025-05-22 12:37, Arthur Schwarz via Cygwin wrote:
> > I can't figure this one out.
> >
> > > clear;g++ -flinker-output=dyn -o slip.dll *.o
> >
> > generates:
> >
> >
/usr/lib/gcc/x86_64-pc-cygwin/12/../../../../x86_64-pc-cygwin/bin/ld:
/usr/lib/
> > gcc/x86_64-pc-cygwin/12/../../../../lib/libcygwin.a(libcmain.o): in
function
> > `main':
> > /usr/src/debug/cygwin-3.6.1-1/winsup/cygwin/lib/libcmain.c:37:
> > (.text.startup+0x79): undefined reference to `WinMain'
> > collect2: error: ld returned 1 exit status
> >
> > But I am developing a dll, not a windows application. The gcc.pdf
manual says:
> >
> > -flinker-output=type
> > This option controls code generation of the link-time optimizer. By
> > default the
> > linker output is automatically determined by the linker plugin. For
> > debugging
> > the compiler and if incremental linking with a non-LTO object file
> > is desired,
> > it may be useful to control the type manually.
> >
> > If type is ‘dyn’, code generation produces a shared library. In
this
> > case ‘-fpic’
> > or ‘-fPIC’ is preserved, but not enabled automatically. This allows
> > to build
> > shared libraries without position-independent code on architectures
> > where this
> > is possible, i.e. on x86.
> >
> > My code is not executable and nowhere links to or uses any Windows
code. It does
> > not have a WinMain method and there is no link to libcmain.o in the
object
> > folder (*.o does not have libcmain.o).
> >
> > How do I get rid of this link error?
> On 2025-05-22 19:19:46 Brian Inglis via Cygwin wrote:
>
> Tell the linker (ld/gcc/g++) not the LTO code generator!
> If your "code" is not executable (data?) then LTO is irrelevant.
>
> Please note:
>
> $ info gcc flinker-output | tail -8
> ---------- Footnotes ----------
>
> (1) On some systems, ‘gcc -shared’ needs to build supplementary stub
> code for constructors to work.
> On multi-libbed systems, ‘gcc -shared’ must select the correct
support libraries
> to link against.
> *Failing to supply the correct flags may lead to subtle defects.*
> Supplying them in cases where they are not necessary is innocuous.
>
> A couple of examples from cygport scripts:
>
> $ grep -iA3 'CC.*-shared' **/*.cygport
> expect.cygport: cygmake SHLIB_LD='$(CC) -shared -Wl,--out-implib,$@.a'
> --
> libvpx.cygport: $CC -shared -fpic -o cygvpx-$ABI.dll \
> libvpx.cygport- -Wl,--out-implib,libvpx.dll.a \
> libvpx.cygport- -Wl,--whole-archive,libvpx.a,--no-whole-archive \
> libvpx.cygport- -Wl,--version-script,$EXPORT_FILE
>
> Your program will need to link with the implib.
>
> --
> Take care. Thanks, Brian Inglis Calgary, Alberta, Canada
>
> La perfection est atteinte Perfection is achieved
> non pas lorsqu'il n'y a plus rien à ajouter not when there is no
more to add
> mais lorsqu'il n'y a plus rien à retrancher but when there is no
more to cut
> -- Antoine de Saint-Exupéry
Thanks!
> g++ -shared -flinker-output=dyn -o slip.dll *.o
ran with not errors.
Is there any documentation available on cygwin specific issues? This
seems like
a question that I should be able to answer on my own. One residual
question that
a cygwin specific manual may answer is why libcmain.a was included at all.
art
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