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* [PATCH] libstdc++: Use LTLIBICONV when linking libstdc++.so [PR93602]
@ 2022-04-13 14:23 Jonathan Wakely
  2022-04-20 12:56 ` Jonathan Wakely
  0 siblings, 1 reply; 4+ messages in thread
From: Jonathan Wakely @ 2022-04-13 14:23 UTC (permalink / raw)
  To: libstdc++, gcc-patches

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


^ permalink raw reply	[flat|nested] 4+ messages in thread
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-- links below jump to the message on this page --
2022-04-13 14:23 [PATCH] libstdc++: Use LTLIBICONV when linking libstdc++.so [PR93602] Jonathan Wakely
2022-04-20 12:56 ` Jonathan Wakely
2022-04-21 10:13   ` Yubin Ruan
2022-04-21 10:15     ` Jonathan Wakely

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