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

[Yubin Ruan]

Hi,

Will this be in GCC12?

--
Yubin

On Wed, Apr 20, 2022 at 8:58 PM Jonathan Wakely via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> 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
> >
>