Re: Segmentation fault of shared libraries

[Arthur Gold <agold at bga dot com>]

Song:

One thing to try (and it may not work either; I've had my share of fun
with shared object doing ugly things behind my back):

Run a program that links to the library under gdb, and before you
actually run any code, do a 'break _init', _init being the first thing
(after static initialization) that happens in an .so (i.e. before the
'main' of the real program).

Otherwise, look for anything you're initializing statically within the
library.

HTH,
--ag


wsonguci@my-deja.com wrote:
> 
> In article <864sfd9mdi.fsf@hwiw01.hyperwave.com>,
>   Joerg Faschingbauer <jfasch@hyperwave.com> wrote:
> > wsonguci@my-deja.com writes:
> >
> > > Hi, folks
> > >
> > > I used gcc/g++ 2.8.1 to build a shared library under solaris 7 x86
> like:
> > > g++ -g -D_REENTRANT -fpic -shared -o libmylib.so file1.o file2.o
> > >
> > > Then I used a main.cpp to test the shared library like
> > > g++ -g -o main main.cpp -lmylib
> > >
> > > But when I run 'main', I got 'Segmentation fault (core dumped)'.
> > > It happens even before main() function gets executed. I guess
> > > it happens when the run-time system tries to load the shared
> > > library libmylib.so. ( I tried to use dlopen
> ("libmylib.so",RTLD_LAZY),
> > > the same problem happened when dlopen was called )
> > >
> > > Could anyone help me how to figure this out? Are there any
> > > special compiler or linker switches to build the shared library?
> >
> > Have you tried gdb?
> >
> > When a C++ shared library is loaded (either by the dynamic loader or
> > explicitly), constructors of global objects get called. It's not
> > always trivial to ensure that this happens correctly (i.e., in the
> > right order) because a global object of class A might depend a global
> > object of class B being already initialized. C++ makes no guarantees
> > about in which order the ctors in file1.o and file2.o are
> > called. (Though it guarantees that the ctors in, say, file1.o itself
> > are called in order of declaration.)
> >
> > Joerg
> >
> 
> Hi, Joerg
> 
> Thanks for the suggestion.
> 
> I tried 'gdb main core'. After 'Reading symbols from ....',
> Gdb shows '#0 0x0 in ?? ()'
> 
> Actually the segmentation fault happens before any statements
> in the main() function of the main.cpp, because it happened even
> I put 'return 0' as the first statement in the main() function.
> 
> -Song
> 
> Sent via Deja.com http://www.deja.com/
> Before you buy.

-- 
Artie Gold, Austin, TX
mailto:agold@bga.com or mailto:agold@cs.utexas.edu
--
"If you come to a fork in the road, take it." L. P. Berra