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Subject:	Re: environ: fix link error on 64-bit Cygwin
To:	The Cygwin Mailing List <cygwin AT cygwin DOT com>
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From:	Eric Blake <eblake AT redhat DOT com>
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Date:	Wed, 31 Jan 2018 07:52:51 -0600
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From: Eric Blake <eblake AT redhat DOT com>
To: The Cygwin Mailing List <cygwin AT cygwin DOT com>
Message-ID: <0d2666a8-1037-fc9c-a17f-72cc59e9d977 AT redhat DOT com>
Subject: Re: environ: fix link error on 64-bit Cygwin
References: <36131639 DOT liFsmjX0ip AT omega>
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Forwarding from the gnulib list; is this something we should fix in
cygwin proper?

On 01/31/2018 04:42 AM, Bruno Haible wrote:
> On 64-bit Cygwin, a libunistring build fails like this:
>=20
> $ /bin/sh ../libtool  --tag=3DCC --preserve-dup-deps  --mode=3Dlink x86_6=
4-pc-cygwin-gcc  -g -O2  -L/usr/local/cygwin64/lib -Wl,--disable-auto-impor=
t -o test-environ.exe test-environ.o libtests.a ../lib/libunistring.la libt=
ests.a
> libtool: link: x86_64-pc-cygwin-gcc -g -O2 -Wl,--disable-auto-import -o .=
libs/test-environ.exe test-environ.o  -L/usr/local/cygwin64/lib libtests.a =
../lib/.libs/libunistring.dll.a -liconv libtests.a -L/usr/local/cygwin64/lib
> test-environ.o:test-environ.c:(.rdata$.refptr.environ[.refptr.environ]+0x=
0): undefined reference to `environ'
> collect2: error: ld returned 1 exit status
>=20
> This fixes it.
>=20
>=20
> 2018-01-31  Bruno Haible  <bruno AT clisp DOT org>
>=20
> 	environ: Fix link error on 64-bit Cygwin.
> 	* lib/unistd.in.h (environ): On Cygwin, redeclare with the
> 	__declspec(dllimport) attribute.
> 	* doc/posix-functions/environ.texi: Mention the Cygwin problem.
>=20
> diff --git a/doc/posix-functions/environ.texi b/doc/posix-functions/envir=
on.texi
> index 34ac25a..a6c0095 100644
> --- a/doc/posix-functions/environ.texi
> +++ b/doc/posix-functions/environ.texi
> @@ -24,6 +24,9 @@ shared libraries on Mac OS X 10.5.  Here is a workaroun=
d: Instead, one can use
>  #define environ (*_NSGetEnviron())
>  @end smallexample
>  This works at all versions of Mac OS X.
> +@item
> +On Cygwin in 64-bit mode, references to this variable cause a link error=
 when
> +the option @code{-Wl,--disable-auto-import} is in use.
>  @end itemize
>=20=20
>  Portability problems not fixed by Gnulib:
> diff --git a/lib/unistd.in.h b/lib/unistd.in.h
> index 6802e3b..4ef0ffa 100644
> --- a/lib/unistd.in.h
> +++ b/lib/unistd.in.h
> @@ -400,6 +400,13 @@ _GL_WARN_ON_USE (dup3, "dup3 is unportable - "
>=20=20
>=20=20
>  #if @GNULIB_ENVIRON@
> +# if defined __CYGWIN__
> +/* The 'environ' variable is defined in a DLL. Therefore its declaration=
 needs
> +   the '__declspec(dllimport)' attribute, but the system's <unistd.h> la=
cks it.
> +   This leads to a link error on 64-bit Cygwin when the option
> +   -Wl,--disable-auto-import is in use.  */
> +_GL_EXTERN_C __declspec(dllimport) char **environ;
> +# endif
>  # if !@HAVE_DECL_ENVIRON@
>  /* Set of environment variables and values.  An array of strings of the =
form
>     "VARIABLE=3DVALUE", terminated with a NULL.  */
>=20
>=20
>=20

--=20
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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