[lfs] 02/07: mips64el: hack pass 2 libstdc++.so to use libgcc_s.so

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git pushed a commit to branch xry111/mips64el
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commit 4f878a8639db32da251a50fc3f0b33db89593c5d
Author: Xi Ruoyao <[email protected]>
AuthorDate: Mon Feb 2 18:06:12 2026 +0800

    mips64el: hack pass 2 libstdc++.so to use libgcc_s.so
    
    I'm still not so sure about why this is only needed for MIPS.  For the
    record: if an application links to both libgcc_s.so and a "LFS GCC
    pass2" libstdc++.so (using libgcc_eh.a instead of libgcc_s.so), there
    will be two copies of some data structures used for unwinding, one in
    libgcc_s.so and another in libstdc++.so (linked from libgcc_eh.a).  On
    MIPS it seems only the copy in libgcc_s.so is initialized (at program
    startup), thus when the C++ exception handling code in libstdc++.so
    starts to unwind, it will crash immediately.  Somehow this issue does
    not show up on all other architectures where I've tried LFS.
---
 chapter06/gcc-pass2.xml | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/chapter06/gcc-pass2.xml b/chapter06/gcc-pass2.xml
index 6ef3d7c8b..6c16cbca7 100644
--- a/chapter06/gcc-pass2.xml
+++ b/chapter06/gcc-pass2.xml
@@ -157,6 +157,34 @@ cd       build</userinput></screen>
 
 <screen><userinput remap="make">make</userinput></screen>
 
+    <!-- The GCC manual actually states if the application needs to throw
+         and catch exceptions across different shared libraries, libgcc_s
+         must be used.  Thus it seems on all architectures we should link
+         libstdc++ against libgcc_s.  But on all other architectures I've
+         tested, the exception handling seems fine even with the static
+         libgcc and libgcc_eh libraries (as long as they are from GCC pass 2
+         instead of pass 1, see LDFLAGS_FOR_TARGET).  Maybe this is actually
+         some sort of bug in the MIPS toolchain or an inhernet limitation
+         of the MIPS ABI (a spaghetti with some aspects traceable to SGI
+         IRIX).  -->
+    <para>The <command>libtool</command> copy for building the C++ runtime
+    library was configured with GCC pass 1 as the compiler.  GCC pass 1
+    lacks the shared GCC runtime library
+    (<filename class='libraryfile'>libgcc_s.so</filename>), so the
+    <command>libtool</command> copy has linked the C++ runtime library
+    against the static libraries
+    <filename class='libraryfile'>libgcc.a</filename> and
+    <filename class='libraryfile'>libgcc_eh.a</filename> instead.  The
+    result is insufficiant for the correct exception handling on MIPS,
+    causing glibc tests to fail.  To allow testing glibc, edit the
+    <command>libtool</command> copy and rebuild the C++ runtime library with
+    <filename class='libraryfile'>libgcc_s.so</filename> instead of the
+    static libraries:</para>
+
+<screen><userinput>sed '/postdeps=/s/-lgcc/&amp;_s/g' -i $LFS_TGT/libstdc++-v3/libtool
+rm $LFS_TGT/libstdc++-v3/src/libstdc++.la
+make -C $LFS_TGT/libstdc++-v3 src/libstdc++.la</userinput></screen>
+
     <para>Install the package:</para>
 
 <screen><userinput remap="install">make DESTDIR=$LFS install</userinput></screen>

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