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?
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
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