ncurses: Don't create library aliases in an unsafe mannerxry111/ncurses-disallow-abi-mismatch

TL;DR DO NOT REVERT THIS COMMIT BECAUSE IT MAKES A BLFS PACKAGE FTBFS!

The ABI of libncurses and libncursesw (et al) are different so it's
unsafe to use libncursesw as a drop-in of libncurses.  If an application
is built with -D_XOPEN_SOURCES={a number >= 500} or
-D_XOPEN_SOURCES_EXTENDED, it should use libncursesw; otherwise it
should use libncurses.  Otherwise there will be an ABI mismatch and it
may cause segfault etc.

An exception: the terminfo (terminal capability database) support in
libncursesw and libncurses are the same.  Thus the distros providing
both libncursesw and libncurses configure Ncurses --with-termlib so the
terminfo support will be a standalone libtinfo library, instead of being
duplicated in two ncurses libraries.  Create a symlink so the packages
only using terminfo support from ncurses can find the libncursesw
library and use it.

If a BLFS package using libncurses FTBFS after this change, we need to
define -D_XOPEN_SOURCES=600 (as pkg-config --cflags ncursesw outputs),
before hacking it to use libncursesw instead.

3 files changed, 52 insertions, 13 deletions

diff --git a/chapter01/changelog.xml b/chapter01/changelog.xml
index 15bd9a519..a45affaf1 100644
--- a/chapter01/changelog.xml
+++ b/chapter01/changelog.xml
@@ -41,6 +41,21 @@
     -->
 
     <listitem>
+      <para>2024-01-18</para>
+      <itemizedlist>
+        <listitem>
+          <para>[xry111] - No longer create the ncurses "compatibility"
+          linker scripts which may potentially cause an ABI mismatch.  Fixes
+          <ulink url="&lfs-ticket-root;5415">#5415</ulink>.  Note that if
+          a package fails to build after this change, the package likely
+          had been suffering from the subtle ABI mismatch in the past.  So
+          such build failures should be analyzed case by case, not papered
+          over with the "compatibility" linker scripts.</para>
+        </listitem>
+      </itemizedlist>
+    </listitem>
+
+    <listitem>
       <para>2024-01-09</para>
       <itemizedlist>
         <listitem>
diff --git a/chapter06/ncurses.xml b/chapter06/ncurses.xml
index 8d7c8b1fe..1d4afdda8 100644
--- a/chapter06/ncurses.xml
+++ b/chapter06/ncurses.xml
@@ -156,7 +156,7 @@ popd</userinput></screen>
     <para>Install the package:</para>
 
 <screen><userinput remap="install">make DESTDIR=$LFS TIC_PATH=$(pwd)/build/progs/tic install
-echo "INPUT(-lncursesw)" > $LFS/usr/lib/libncurses.so</userinput></screen>
+ln -sv libncursesw.so $LFS/usr/lib/libtinfo.so</userinput></screen>
 <!--
     <para>Remove an unneeded static library not handled by
     <command>configure</command>:</para>
@@ -176,12 +176,24 @@ echo "INPUT(-lncursesw)" > $LFS/usr/lib/libncurses.so</userinput></screen>
       </varlistentry>
 
       <varlistentry>
-        <term><command>echo "INPUT(-lncursesw)" > $LFS/usr/lib/libncurses.so</command></term>
+        <term><command>ln -sv libncursesw.so $LFS/usr/lib/libtinfo.so</command></term>
         <listitem>
-          <para>The <filename>libncurses.so</filename> library is needed by
-          a few packages we will build soon. We create this small linker
-          script, as this is what is done in <xref
-          linkend="chapter-building-system"/>.</para>
+          <para>On the distros providing both the wide-character
+          <systemitem class='library'>libncursesw</systemitem>
+          and the traditional 8-bit
+          <systemitem class='library'>libncurses</systemitem> libraries,
+          the terminal capability database (terminfo) support
+          functionalities of Ncurses are separated into a library named
+          <systemitem class='library'>libtinfo</systemitem> so they
+          are not duplicated in these two Ncurses libraries.  Thus some
+          packages will refer to
+          <systemitem class='library'>libtinfo</systemitem> for the
+          terminfo support.  On LFS we don't build the 8-bit
+          <systemitem class='library'>libncurses</systemitem> library,
+          so we've configured Ncurses to include the terminfo support
+          in <systemitem class='library'>libncursesw</systemitem>.  Create
+          a symlink for the packages expecting the terminfo support from
+          <systemitem class='library'>libtinfo</systemitem>.</para>
         </listitem>
       </varlistentry>
 
diff --git a/chapter08/ncurses.xml b/chapter08/ncurses.xml
index b51099001..e8d286b6d 100644
--- a/chapter08/ncurses.xml
+++ b/chapter08/ncurses.xml
@@ -105,7 +105,9 @@
           These wide-character libraries are usable in both multibyte and
           traditional 8-bit locales, while normal libraries work properly
           only in 8-bit locales. Wide-character and normal libraries are
-          source-compatible, but not binary-compatible.</para>
+          source-compatible, but not binary-compatible: an application must
+          be recompiled with the proper preprocessor definitions before
+          being linked against the wide-character libraries.</para>
         </listitem>
       </varlistentry>
 
@@ -138,15 +140,25 @@ install -vm755 dest/usr/lib/libncursesw.so.&ncurses-version; /usr/lib
 rm -v  dest/usr/lib/libncursesw.so.&ncurses-version;
 cp -av dest/* /</userinput></screen>
 
-    <para>Many applications still expect the linker to be able to find
-    non-wide-character Ncurses libraries. Trick such applications into linking with
-    wide-character libraries by means of symlinks and linker scripts:</para>
+    <para>For applications looking up 8-bit Ncurses libraries via
+    <command>pkg-config</command>, create several symlinks so
+    <command>pkg-config</command> will output the information of the
+    wide-character Ncurses libraries instead.  This is safe because
+    <command>pkg-config</command> also provides the <envar>CFLAGS</envar>,
+    including the preprocessor definitions needed to ensure the application
+    code compiled with the same ABI as the wide-character libraries:</para>
+
+    <!-- For apps directly using -lncurses w/o querying pkg-config, we
+         must tell them to use -D_XOPEN_SOURCE=600 and -lncursesw explicitly
+         to avoid an ABI mismatch.  We shall handle them case by case.  -->
 
 <screen><userinput remap="install">for lib in ncurses form panel menu ; do
-    rm -vf                    /usr/lib/lib${lib}.so
-    echo "INPUT(-l${lib}w)" &gt; /usr/lib/lib${lib}.so
     ln -sfv ${lib}w.pc        /usr/lib/pkgconfig/${lib}.pc
 done</userinput></screen>
+<!--
+
+    commented out because using libncursesw.so for libcurses.so is unsafe,
+    and there shouldn't be "old" apps searching for "libcursesw".
 
     <para>Finally, make sure that old applications that look for
     <filename class="libraryfile">-lcurses</filename> at build time are still
@@ -155,7 +167,7 @@ done</userinput></screen>
 <screen><userinput remap="install">rm -vf                     /usr/lib/libcursesw.so
 echo "INPUT(-lncursesw)" &gt; /usr/lib/libcursesw.so
 ln -sfv libncurses.so      /usr/lib/libcurses.so</userinput></screen>
-
+-->
     <para>If desired, install the Ncurses documentation:</para>
 
 <screen><userinput remap="install">cp -v -R doc -T /usr/share/doc/ncurses-&ncurses-version;</userinput></screen>