[Bug c++/26755] New: [4.1 regression?] may fail to generate code for base destructor defined inline

["debian-gcc at lists dot debian dot org" <gcc-bugzilla at gcc dot gnu dot org>]

[ no small test case yet, forwarded from http://bugs.debian.org/356435 ]

Where a base class has a destructor defined inline, g++ may generate
code for a derived class's destructor that calls an non-inline version
of the base class destructor, but without generating code for the
latter.  This is normally masked by the fact that g++ 4.1 now
generates the base-class destructor (aka the non-in-charge destructor)
along with the whole-object destructor (aka the in-charge
destructor), but becomes a problem when linking with code generated by
g++ 4.0.

An example for this is bug #356245 (xbsql failing to build):

> Automatic build of xbsql_0.11-5 on bigsur by sbuild/mips 1.80
...
> /bin/sh ../libtool --mode=link g++  -UNO_READLINE -I/usr/local/include -g  -g -o xql  xql.o -lxbase -lreadline -lncurses ./libxbsql.la 
> g++ -UNO_READLINE -I/usr/local/include -g -g -o .libs/xql xql.o  -lreadline -lncurses ./.libs/libxbsql.so /usr/lib/libxbase.so
> ./.libs/libxbsql.so: undefined reference to `xbNdx::~xbNdx()'
> collect2: ld returned 1 exit status
> make[2]: *** [xql] Error 1

Ben Hutchings:

I was scratching my head over this one for a long time, because
libxbase.so definitely does include an out-of-line copy of the
destructor (required for the vtable).  Eventually I remembered that the
destructor can be called in several different ways and that the G++ ABI
provides separate entry points, each with its own symbol, for those
different cases.  These aren't distinguished when demangling, so we must
turn that off to see that:

libxbase built with g++ 4.0 has:
0001e940 W _ZN5xbNdxD0Ev  // deleting destructor
0001eb30 W _ZN5xbNdxD1Ev  // complete object destructor

libxbsql built with g++ 4.0 has:
00015676 W _ZN5xbNdxD1Ev  // complete object destructor
00012aec W _ZN5xbNdxD2Ev  // base object destructor

libxbase (built with g++ 4.1) has:
0001f850 W _ZN5xbNdxD0Ev  // deleting destructor
0001f8e0 W _ZN5xbNdxD1Ev  // complete object destructor
0001f960 W _ZN5xbNdxD2Ev  // base object destructor

libxbsql (built with g++ 4.1) has:
         U _ZN5xbNdxD1Ev  // complete object destructor
         U _ZN5xbNdxD2Ev  // base object destructor

It appears that g++ 4.1 generates out-of-line code for all inline
destructors along with other members of the class and relies on that
avoid generating duplicates elsewhere.  But g++ 4.1 is supposed to be
binary-compatible with g++ 4.0 and this behaviour isn't, so this is a
bug in g++.

Ben.


-- 
           Summary: [4.1 regression?] may fail to generate code for base
                    destructor defined inline
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: debian-gcc at lists dot debian dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26755