Re: __attribute__((constructor)), shared object files and C++...

[Muthukumar Ratty <muthu at iqmail dot net>]

Hi Daniel,

I have one more question about this for the C example

I did ...

	ld -shared -soname libtest.so.1 -o libtest.so.1.0 -lc libtest.o

and looked into the generated ELF file for this case and found that it
lacks .init and .fini sections which has the constructors and destructors.
So I tried the following

    gcc -shared -Wl,-soname -Wl,libtest.so.1 -o libtest.so.1.0 -lc libtest.o

and I see the .init and .fini sections and the executable calls the
constructors and destructors correctly.

So ld doesnt recognize __attribute__ key word? Any idea how to make it
work? (looking at the ld manual, i got the idea that it may be possible using
__CTORS_LIST__ etc. in the linker script? Is that right?

Thanks,
Muthu




On Wed, 7 May 2003, Daniel Jacobowitz wrote:

> Scott, the problem's pretty easy: always, always link with the
> appropriate driver.  Don't use ld -shared or gcc to link C++ code.  Use
> g++.  If you want a soname, add -Wl,-soname,libtest.so.1.
>
> Whatever howto you were working from is wrong, and should be corrected.
>
> On Wed, May 07, 2003 at 10:16:05AM -0700, Muthukumar Ratty wrote:
> >
> >
> > Hi, Posting this in gcc list for experts.
> > thanks,
> > Muthu.
> >
> >
> > ---------- Forwarded message ----------
> > Date: Tue, 6 May 2003 16:25:53 -0700
> > From: "Pearson, Scott" <scott.pearson@intel.com>
> > To: "'gcc-help@gcc.gnu.org'" <gcc-help@gcc.gnu.org>
> > Subject: __attribute__((constructor)), shared object files and C++...
> >
> >
> > Hi
> >
> > I have encountered a pair of related problems producing a shared object (SO)
> > file which exposes a C++ class.
> >
> > First, consider the following non-C++ example. Here's the source for the SO
> > file (libtest.c):
> >
> >  <<libtest.c>>
> > And here's the source for the test program (test.c):
> >
> >  <<test.c>>
> > If I build the SO file and test program using a command sequence supporting
> > versioning (as is shown in the Shared Object File HOW-TO), such as:
> >
> > 		gcc -fPIC -c libtest.c
> > 		ld -shared -soname libtest.so.1 -o libtest.so.1.0 -lc
> > libtest.o
> > 		ldconfig -v -n .
> > 		ln -sf libtest.so.1 libtest.so
> > 		gcc -o test test.c -L. -ltest
> >
> >  Then I will see (only) the following output:
> >
> > 	In main()
> > 	In Test()
> >
> > As you can see, the constructor and destructor I included in the SO file are
> > not executed.
> >
> > If, however, I build the application without SO versioning, using the
> > more-basic set of commands:
> >
> > 	gcc -fPIC -c libtest.c
> > 	gcc -shared -o libtest.so libtest.o
> > 	gcc -o test test.c -L. -ltest
> >
> > Then I will see the following output:
> >
> > 	In InitSO()
> > In main()
> > 	In Test()
> > 	In ExitSO()
> >
> > As you can see, the constructor and destructor that I included in the SO
> > file are, in this case, properly executed.
> >
> >
> > That's problem #1; now, let's look at the C++ case. Here's the SO file
> > source (libctest.cpp):
> >
> >  <<libctest.cpp>>
> > And here's the include file (libctest.h; which defines the class):
> >
> >  <<libctest.h>>
> > And, finally, the test program (ctest.cpp):
> >
> >  <<ctest.cpp>>
> > I build the SO file and test program using the following commands, similar
> > to the (working) non-C++ example above:
> >
> > 	gcc -fPIC -c libctest.cpp
> > 	gcc -shared -o libctest.so libctest.o
> > 	gcc -o ctest -L. -lctest -lstdc++ ctest.cpp
> >
> > The output I get is:
> >
> > 	In cTest::cTest()
> > 	In main()
> > 	In cTest::Test()
> > 	In cTest::~cTest()
> >
> > As you can see, the (module-level) constructor and destructor in the SO file
> > are NOT executed.
> >
> > Does anyone have any insights into what's going wrong here?
> >
> > TIA,
> > Scott
> >
> > N. Scott Pearson
> > Staff S/W Architect, Intel Desktop Boards Operation
> > Desktop Platform Solutions Division, Intel Corporation
> > Desk    503-696-7818       Cell      503-702-6412
> > Fax      503-696-1015       Email    scott.pearson@intel.com
> > <mailto:scott.pearson@intel.com>
> >
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