DMARC-Filter:	OpenDMARC Filter v1.4.2 delorie.com 54MJKsYJ390079
Authentication-Results:	delorie.com; dmarc=pass (p=none dis=none) header.from=cygwin.com
Authentication-Results:	delorie.com; spf=pass smtp.mailfrom=cygwin.com
DKIM-Filter:	OpenDKIM Filter v2.11.0 delorie.com 54MJKsYJ390079
Authentication-Results:	delorie.com;
	dkim=pass (1024-bit key, unprotected) header.d=cygwin.com header.i=@cygwin.com header.a=rsa-sha256 header.s=default header.b=PLBsFDmg
X-Recipient:	archive-cygwin AT delorie DOT com
DKIM-Filter:	OpenDKIM Filter v2.11.0 sourceware.org 510FD385772F
DKIM-Signature:	v=1; a=rsa-sha256; c=relaxed/relaxed; d=cygwin.com;
	s=default; t=1747941653;
	bh=RyRsE8v8f+10lC/ILCVDMuwxPQjHpspF/Rh673PvFag=;
	h=Date:Subject:To:References:In-Reply-To:List-Id:List-Unsubscribe:
	List-Archive:List-Post:List-Help:List-Subscribe:From:Reply-To:Cc:
	From;
	b=PLBsFDmgZNGMpfDCC3rBLxKHpwxv30RniKxPktlqb0ceybX58/5sU4+uakWs9APac
	+5zsQ8AzkbwvktGXPVom+th5rJqXgSpQyqlbmk442R3zjr6iz8Koh98102NVhOhD83
	4TI1mqr5r8LAMjLpmQ4WJ1q6JyAmVYfJDNEAa08c=
X-Original-To:	cygwin AT cygwin DOT com
Delivered-To:	cygwin AT cygwin DOT com
DMARC-Filter:	OpenDMARC Filter v1.4.2 sourceware.org 83FAA3857B9E
ARC-Filter:	OpenARC Filter v1.0.0 sourceware.org 83FAA3857B9E
ARC-Seal:	i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1747941589; cv=none;
	b=svszZ7EqqVSXTntot9k7yLhSBvmfbSbHFAN9irn1QRE4b18FdGxRHEkjANq3lX43NqLhSNKyVSijbwZMlcSyE+sL1RRXO/KR6kTG4RiBHivU7IpK08E8JLSXJrFvOaGSmDv4piUBEcMGM12qgS8n0rYH0gih9o1Y8lcG0PTFW44=
ARC-Message-Signature:	i=1; a=rsa-sha256; d=sourceware.org; s=key;
	t=1747941589; c=relaxed/simple;
	bh=LszgQ3Na6nZq+2cCE0uE8eOM4PzDvLQWSZ1OXkdI9Z4=;
	h=Message-ID:Date:MIME-Version:From:Subject:To:DKIM-Signature;
	b=Urix/1wsxveyRwNr8whRRLKKtJg3EJpw9fhjd8v/DDPZzk252gfbyl1VGldlEhYtK1ZAzWDUirs02S0wP65brZWlcgUpMxMPkSP2kBHe/bP5Pw08bd5I9tLhNL+kFDRgHVvKpGPBtwOHyqLmXaiy6E/PrsOfRdRH3F371s5xHWk=
ARC-Authentication-Results:	i=1; server2.sourceware.org
DKIM-Filter:	OpenDKIM Filter v2.11.0 sourceware.org 83FAA3857B9E
Message-ID:	<24d8214c-476a-4d6b-8fc0-be2c4320d52c@SystematicSW.ab.ca>
Date:	Thu, 22 May 2025 13:19:46 -0600
MIME-Version:	1.0
User-Agent:	Mozilla Thunderbird
Subject:	Re: gcc links to libcmain when generating a dll
To:	cygwin AT cygwin DOT com
References:	<5b9f8d4b-0a5a-4aea-99cb-f2c24a6a127a AT slipbits DOT com>
Organization:	Systematic Software
In-Reply-To:	<5b9f8d4b-0a5a-4aea-99cb-f2c24a6a127a@slipbits.com>
X-Rspamd-Server:	rspamout03
X-Rspamd-Queue-Id:	9ED372000E
X-Stat-Signature:	dgr6ud7g7djaptgidwp9c7c9z785faym
X-Session-Marker:	427269616E2E496E676C69734053797374656D6174696353572E61622E6361
X-Session-ID:	U2FsdGVkX18I4x61s1ThZp5YORgKVeAkDKdAckpfJ94=
X-HE-Tag:	1747941587-269950
X-HE-Meta:	U2FsdGVkX18Y4dqZeUWSP9aKsJCPJUHnFVpMwm9BH3fJmH4TlyKblCUsWIBFrI+spvvtg4JrNm1VZuj4yFZPdg8w9pEw0l+kWZ9zbdju7upp2VY9ubR/kHKfhuDwB99ABeuz8dHI7Yj+r5aLzuEw/JBEDQPf81VJm3O3Htqo9VE96mWCcVlw/S+XvGMIz4yCF4Fus2NKfgl+iHcewyCn+ZtK4Dtfw+kBba7/Wwj+SfHcC3peLntAXr7xx7rf9cLCaM2nVud1zyhzepsPQeNz2cbKZq8e5+fcVHbUfFkKZUAGlOPtJ2aumEVemM6hCOiCkfKLK/4skhTM3xYkCAvh1aM0+5H9ZgYL
X-BeenThere:	cygwin AT cygwin DOT com
X-Mailman-Version:	2.1.30
List-Id:	General Cygwin discussions and problem reports <cygwin.cygwin.com>
List-Unsubscribe:	<https://cygwin.com/mailman/options/cygwin>,
	<mailto:cygwin-request AT cygwin DOT com?subject=unsubscribe>
List-Archive:	<https://cygwin.com/pipermail/cygwin/>
List-Post:	<mailto:cygwin AT cygwin DOT com>
List-Help:	<mailto:cygwin-request AT cygwin DOT com?subject=help>
List-Subscribe:	<https://cygwin.com/mailman/listinfo/cygwin>,
	<mailto:cygwin-request AT cygwin DOT com?subject=subscribe>
From:	Brian Inglis via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	cygwin AT cygwin DOT com
Cc:	Brian Inglis <Brian DOT Inglis AT SystematicSW DOT ab DOT ca>
Errors-To:	cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com
Sender:	"Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>
X-MIME-Autoconverted:	from base64 to 8bit by delorie.com id 54MJKsYJ390079

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

-- 
Problem reports:      https://cygwin.com/problems.html
FAQ:                  https://cygwin.com/faq/
Documentation:        https://cygwin.com/docs.html
Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple

- Raw text -