[Bug c++/31774] New: inconsitency between gcc and g++ when linking with --as-needed

["pva at gentoo dot org" <gcc-bugzilla at gcc dot gnu dot org>]

I have problems linking executable with C++ library with --as-needed ld flag
while linking with gcc succeeds. During investigation I found inconsistency in
gcc and g++ calls concerning --as-needed. First I will show you what I do next
I'll summarize what is this bug about:

* What I do:
First I compile/link objects which will be included in library:

libtool --mode=compile i686-pc-linux-gnu-g++ -c -g -O2 -pthread sync.cpp 
 i686-pc-linux-gnu-g++ -c -g -O2 -pthread sync.cpp  -fPIC -DPIC -o .libs/sync.o 
 i686-pc-linux-gnu-g++ -c -g -O2 -pthread sync.cpp -o sync.o >/dev/null 2>&1 

All objects I linked in the same way. Next library is linked itself
(I've edited output to simplify reading so there could be some typos):

libtool --mode=link i686-pc-linux-gnu-g++ -o libgigabase_r.la class.lo
  compiler.lo database.lo replicator.lo hashtab.lo file.lo symtab.lo 
  btree.lo rtree.lo cursor.lo query.lo pagepool.lo wwwapi.lo unisock.lo 
  blob.lo container.lo exception.lo localcli.lo sync.lo -pthread
  -rpath /usr/lib -version-info 2
i686-pc-linux-gnu-g++ -shared 
  -nostdlib /usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../crti.o
  /usr/lib/gcc/i686-pc-linux-gnu/4.1.2/crtbeginS.o
  .libs/class.o .libs/compiler.o .libs/database.o .libs/replicator.o
  .libs/hashtab.o .libs/file.o .libs/symtab.o .libs/btree.o
  .libs/rtree.o .libs/cursor.o .libs/query.o .libs/pagepool.o
  .libs/wwwapi.o .libs/unisock.o .libs/blob.o .libs/container.o
  .libs/exception.o .libs/localcli.o .libs/sync.o 
  -L/usr/lib/gcc/i686-pc-linux-gnu/4.1.2
  -L/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../../i686-pc-linux-gnu/lib
  -L/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../.. -lstdc++ -lm -lc
  -lgcc_s /usr/lib/gcc/i686-pc-linux-gnu/4.1.2/crtendS.o
  /usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../crtn.o  -pthread
  -Wl,-soname -Wl,libgigabase_r.so.2 -o .libs/libgigabase_r.so.2.0.0 
(cd .libs && rm -f libgigabase_r.so.2 && ln -s libgigabase_r.so.2.0.0 
  libgigabase_r.so.2) 
(cd .libs && rm -f libgigabase_r.so && ln -s libgigabase_r.so.2.0.0 
  libgigabase_r.so) 
i686-pc-linux-gnu-ar cru .libs/libgigabase_r.a  class.o compiler.o
  database.o replicator.o hashtab.o file.o symtab.o btree.o rtree.o
  cursor.o query.o pagepool.o wwwapi.o unisock.o blob.o container.o
  exception.o localcli.o sync.o 
i686-pc-linux-gnu-ranlib .libs/libgigabase_r.a 
creating libgigabase_r.la 
(cd .libs && rm -f libgigabase_r.la && ln -s ../libgigabase_r.la 
libgigabase_r.la) 

Now I link two programs (subsql and guess) against libgigabase_r.so.
While subsql builds successfully: 

i686-pc-linux-gnu-g++ -c -g -O2 -pthread  subsql.cpp 
i686-pc-linux-gnu-g++ -c -g -O2 -pthread  server.cpp 
libtool --mode=link i686-pc-linux-gnu-g++ -Wl,--as-needed -pthread  -o 
subsql subsql.o server.o libgigabase_r.la 
i686-pc-linux-gnu-g++ -Wl,--as-needed -pthread -o .libs/subsql 
subsql.o server.o  ./.libs/libgigabase_r.so 
creating subsql 

guess programm do not:

i686-pc-linux-gnu-g++ -c -g -O2 -pthread  guess.cpp 
libtool --mode=link i686-pc-linux-gnu-g++ -Wl,--as-needed -pthread  -o 
guess guess.o libgigabase_r.la 
i686-pc-linux-gnu-g++ -Wl,--as-needed -pthread -o .libs/guess 
guess.o  ./.libs/libgigabase_r.so 
./.libs/libgigabase_r.so: undefined reference to `pthread_key_create' 
./.libs/libgigabase_r.so: undefined reference to `pthread_getspecific' 
./.libs/libgigabase_r.so: undefined reference to `pthread_create' 
./.libs/libgigabase_r.so: undefined reference to `pthread_key_delete' 
./.libs/libgigabase_r.so: undefined reference to `pthread_detach' 
./.libs/libgigabase_r.so: undefined reference to `pthread_setspecific' 
./.libs/libgigabase_r.so: undefined reference to `pthread_join' 
collect2: ld returned 1 exit status 
make: *** [guess] Error 1

* What is this bug about:

As you noticed libtool links library with -nostdlib and this dependency on
libpthread is missed in .libs/libgigabase_r.so. On pthreads mailing list I was
assured that it's Ok to avoid this dependency and even sometimes this is
useful.

Why the first linkage succeeds while second not.  I've looked at object files
which are used to build final executables and found the differences between
them. The object sever.o (which is used to build subsql) has pthread_*
functions in elf Symbol table (part of output of readelf -W -a):

00002899  00006602 R_386_PC32             00000000   pthread_create 

and in .symtab: 

   102: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND pthread_create 

while the only object file guess.o (which is used to build guess) do not have
any references to pthread_*().

Why I think this bug is in g++. I found that substitution of g++ to gcc during
last linkage fixes compilation problem. While it seems to be wrong to link C++
program with gcc I've compared verbose output of gcc calls and found that
difference in the output. g++ as well as gcc call collect2 but with a bit
different options. g++ call of collect2 misses this part completely (which
follows after other objects):

--no-as-needed -lpthread -lc -lgcc --as-needed

Just for record both calls here:
============================================================
[pva in ~/gigabase/gigabase]
 $=> i686-pc-linux-gnu-g++ -Wl,--as-needed -pthread -o .libs/guess guess.o 
./.libs/libgigabase_r.so -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-4.1.2/work/gcc-4.1.2/configure
--prefix=/usr --bindir=/usr/i686-pc-linux-gnu/gcc-bin/4.1.2
--includedir=/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/include
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.2
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.2/man
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.2/info
--with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/include/g++-v4
--host=i686-pc-linux-gnu --build=i686-pc-linux-gnu --disable-altivec
--enable-nls --without-included-gettext --with-system-zlib --disable-checking
--disable-werror --enable-secureplt --disable-libunwind-exceptions
--disable-multilib --disable-libmudflap --disable-libssp --disable-libgcj
--enable-languages=c,c++ --enable-shared --enable-threads=posix
--enable-__cxa_atexit --enable-clocale=gnu
Thread model: posix
gcc version 4.1.2 (Gentoo 4.1.2)
 /usr/libexec/gcc/i686-pc-linux-gnu/4.1.2/collect2 --eh-frame-hdr -m elf_i386
-dynamic-linker /lib/ld-linux.so.2 -o .libs/guess
/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../crt1.o
/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../crti.o
/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/crtbegin.o
-L/usr/lib/gcc/i686-pc-linux-gnu/4.1.2 -L/usr/lib/gcc/i686-pc-linux-gnu/4.1.2
-L/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../../i686-pc-linux-gnu/lib
-L/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../.. --as-needed guess.o
./.libs/libgigabase_r.so -lstdc++ -lm -lgcc_s -lgcc -lpthread -lc -lgcc_s -lgcc
/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/crtend.o
/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../crtn.o
./.libs/libgigabase_r.so: undefined reference to `pthread_key_create'
./.libs/libgigabase_r.so: undefined reference to `pthread_getspecific'
./.libs/libgigabase_r.so: undefined reference to `pthread_create'
./.libs/libgigabase_r.so: undefined reference to `pthread_key_delete'
./.libs/libgigabase_r.so: undefined reference to `pthread_detach'
./.libs/libgigabase_r.so: undefined reference to `pthread_setspecific'
./.libs/libgigabase_r.so: undefined reference to `pthread_join'
collect2: ld returned 1 exit status
[pva in ~/gigabase/gigabase]
 $=> i686-pc-linux-gnu-gcc -Wl,--as-needed -pthread -o .libs/guess guess.o 
./.libs/libgigabase_r.so -v
Using built-in specs.
Target: i686-pc-linux-gnu
Configured with: /var/tmp/portage/sys-devel/gcc-4.1.2/work/gcc-4.1.2/configure
--prefix=/usr --bindir=/usr/i686-pc-linux-gnu/gcc-bin/4.1.2
--includedir=/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/include
--datadir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.2
--mandir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.2/man
--infodir=/usr/share/gcc-data/i686-pc-linux-gnu/4.1.2/info
--with-gxx-include-dir=/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/include/g++-v4
--host=i686-pc-linux-gnu --build=i686-pc-linux-gnu --disable-altivec
--enable-nls --without-included-gettext --with-system-zlib --disable-checking
--disable-werror --enable-secureplt --disable-libunwind-exceptions
--disable-multilib --disable-libmudflap --disable-libssp --disable-libgcj
--enable-languages=c,c++ --enable-shared --enable-threads=posix
--enable-__cxa_atexit --enable-clocale=gnu
Thread model: posix
gcc version 4.1.2 (Gentoo 4.1.2)
 /usr/libexec/gcc/i686-pc-linux-gnu/4.1.2/collect2 --eh-frame-hdr -m elf_i386
-dynamic-linker /lib/ld-linux.so.2 -o .libs/guess
/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../crt1.o
/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../crti.o
/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/crtbegin.o
-L/usr/lib/gcc/i686-pc-linux-gnu/4.1.2 -L/usr/lib/gcc/i686-pc-linux-gnu/4.1.2
-L/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../../i686-pc-linux-gnu/lib
-L/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../.. --as-needed guess.o
./.libs/libgigabase_r.so -lgcc --as-needed -lgcc_s --no-as-needed -lpthread -lc
-lgcc --as-needed -lgcc_s --no-as-needed
/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/crtend.o
/usr/lib/gcc/i686-pc-linux-gnu/4.1.2/../../../crtn.o
[pva in ~/gigabase/gigabase]
 $=>
============================================================

That is the inconsistency between gcc and g++.

[1]
http://groups.google.com/group/comp.programming.threads/browse_thread/thread/5243754283a02465/5d73e8a1425663fe#5d73e8a1425663fe

Thank you very much for your time,
Peter.


-- 
           Summary: inconsitency between gcc and g++ when linking with --as-
                    needed
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: pva at gentoo dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31774