Re: [PATCH] libstdc++: Use LTLIBICONV when linking libstdc++.so [PR93602]

[Jonathan Wakely <jwakely@redhat.com>]

Pushed to trunk now.

On Wed, 13 Apr 2022 at 15:24, Jonathan Wakely via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Tested x86_64-linux, without libiconv installed, with libiconv installed,
> with libiconv installed but using an in-tree libiconv, with libiconv.a
> installed and using --with-libiconv-type=static, and with libiconv.so
> installed and using --without-libiconv-prefix (which still fails).
>
> I'm not entirely happy about the fact that libtool's LTLIBICONV adds an
> rpath to libstdc++.so, but that can be avoided (as documented by this
> patch) and I don't really see a better solution. Another option would be
> to use -l:libiconv.a if configure defines LTLIBICONV to non-empty and
> the linker supports it, which would *force* the use of a static lib. But
> that seems unnecessarily hostile; not all users will dislike the rpath
> solution. The proposed patch makes it Just Work™ for users who (for
> whatever reason) have installed libiconv, while also allowing them to do
> something more sensible if they care enough to do so.
>
> Thoughts?
>
> -- >8 --
>
> This fixes missing libiconv symbols when libstdc++ is built on a system
> that has libiconv installed. If the libiconv headers are found then
> libstdc++ depends on libiconv_open etc instead of libc's iconv_open. But
> without this fix libstdc++ is not linked to the libiconv library that
> provides the definitions of those symbols.
>
> As discussed in PR 93602 this changed means that libstdc++.so.6 might
> have an rpath pointing to the location of the libiconv.so library. If
> that is not desired, then GCC must be configured to link to a static
> libiconv.a instead, using either --with-libiconv-type=static or an
> in-tree build of libiconv.
>
> libstdc++-v3/ChangeLog:
>
>         PR libstdc++/93602
>         * doc/xml/manual/prerequisites.xml: Document libiconv
>         workarounds.
>         * doc/html/manual/setup.html: Regenerate.
>         * src/Makefile.am (CXXLINK): Add $(LTLIBICONV).
>         * src/Makefile.in: Regenerate.
> ---
> diff --git a/libstdc++-v3/doc/xml/manual/prerequisites.xml b/libstdc++-v3/doc/xml/manual/prerequisites.xml
> index 22e90a7e79d..8799487c821 100644
> --- a/libstdc++-v3/doc/xml/manual/prerequisites.xml
> +++ b/libstdc++-v3/doc/xml/manual/prerequisites.xml
> @@ -48,6 +48,56 @@
>        <varlistentry>
>         <term>linux</term>
>
> +       <listitem>
> +       <para>
> +         The 'gnu' locale model makes use of <function>iconv</function>
> +         for character set conversions. The relevant functions are provided
> +         by Glibc and so are always available, however they can also be
> +         provided by the separate GNU libiconv library. If GNU libiconv is
> +         found when GCC is built (e.g., because its headers are installed
> +         in <filename class="directory">/usr/local/include</filename>)
> +         then the <filename>libstdc++.so.6</filename> library will have a
> +         run-time dependency on <filename>libiconv.so.2</filename>.
> +         If you do not want that run-time dependency then you should do
> +         one of the following:
> +       </para>
> +       <itemizedlist>
> +         <listitem>
> +           <para>
> +             Uninstall the libiconv headers before building GCC.
> +             Glibc already provides <function>iconv</function> so you should
> +             not need libiconv anyway.
> +           </para>
> +         </listitem>
> +         <listitem>
> +           <para>
> +           <link linkend="https://www.gnu.org/software/libiconv/#downloading">
> +           Download</link> the libiconv sources and extract them into the
> +           top level of the GCC source tree, e.g.,
> +           </para>
> +<programlisting>
> +wget https://ftp.gnu.org/pub/gnu/libiconv/libiconv-1.16.tar.gz
> +tar xf libiconv-1.16.tar.gz
> +ln -s libiconv-1.16 libiconv
> +</programlisting>
> +           <para>
> +             This will build libiconv as part of building GCC and link to
> +             it statically, so there is no <filename>libiconv.so.2</filename>
> +             dependency.
> +           </para>
> +         </listitem>
> +         <listitem>
> +           <para>
> +             Configure GCC with <option>--with-libiconv-type=static</option>.
> +             This requires the static <filename>libiconv.a</filename> library,
> +             which is not installed by default. You might need to reinstall
> +             libiconv using the <option>--enable-static</option> configure
> +             option to get the static library.
> +           </para>
> +         </listitem>
> +       </itemizedlist>
> +       </listitem>
> +
>         <listitem>
>         <para>
>           If GCC 3.1.0 or later on is being used on GNU/Linux, an attempt
> diff --git a/libstdc++-v3/src/Makefile.am b/libstdc++-v3/src/Makefile.am
> index 18f57632c3d..9c3f4aca655 100644
> --- a/libstdc++-v3/src/Makefile.am
> +++ b/libstdc++-v3/src/Makefile.am
> @@ -278,7 +278,9 @@ CXXLINK = \
>         $(AM_LIBTOOLFLAGS) $(LIBTOOLFLAGS) \
>         --mode=link $(CXX) \
>         $(VTV_CXXLINKFLAGS) \
> -       $(OPT_LDFLAGS) $(SECTION_LDFLAGS) $(AM_CXXFLAGS) $(LTLDFLAGS) -o $@
> +       $(OPT_LDFLAGS) $(SECTION_LDFLAGS) $(AM_CXXFLAGS) \
> +       $(LTLDFLAGS) $(LTLIBICONV) \
> +       -o $@
>
>  # Symbol versioning for shared libraries.
>  if ENABLE_SYMVERS
>