gcc breakage?? : undefined reference to `__morestack'

Jakub Jelinek jakub at redhat.com
Sun May 15 09:03:51 UTC 2011

On Sat, May 14, 2011 at 07:08:08PM -0400, sean darcy wrote:
> F15 updated.
> gcc-4.6.0-7.fc15.x86_64
> gcc-c++-4.6.0-7.fc15.x86_64
> libgcc-4.6.0-7.fc15.x86_64
> Building kdenlive and mlt (which have built before Thursday) I'm getting
> g++ -shared -Wl,-soname,libmlt++.so.3 -o libmlt++.so.0.7.3 MltConsumer.o 
> MltDeque.o MltEvent.o MltFactory.o MltField.o MltFilter.o 
> MltFilteredConsumer.o MltFilteredProducer.o MltFrame.o MltGeometry.o 
> MltMultitrack.o MltParser.o MltPlaylist.o MltProducer.o MltProfile.o 
> MltProperties.o MltPushConsumer.o MltRepository.o MltService.o 
> MltTokeniser.o MltTractor.o MltTransition.o -Wl,--no-undefined 
> -Wl,--as-needed -L../framework -lmlt
> MltConsumer.o: In function `Mlt::Consumer::get_consumer()':
> MltConsumer.cpp:(.text+0x17): undefined reference to `__morestack'
> ............
> Isn't __morestack an internal gcc reference? It doesn't appear in the 
> mlt source code.

It appears in code that is compiled with -fsplit-stack and is defined in libgcc.a.
Wonder why this library uses it, anyway, if you are linking with g++ instead of
gcc, you probably need to link explicitly against -lgcc, because __morestack is
libgcc.a only symbol, not defined in libgcc_s.so.1.

This isn't something that has changed in gcc for several months, so the only
possible change is on the side of your package or on other libraries it
links against.


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