Bug#116823: Debian's g++-3.0 forgets to generate some code.
On Wed, 24 Oct 2001, Daniel Jacobowitz wrote:
[...]
> > Could you please provide a pointer or two to code samples or things that
> > might be helpful implementing it the Right Way, since I intend to try and
> > fix it? (Dunno if I'm old enough for this, though.)
> >
> > Thanks a lot for all the input, anyways.
>
> The basic trick is to create a section containing pointers to all
> functions you want called. The code to do it is in crtstuff.c in the
> GCC source, but it's a bit on the nasty side. Then you put a symbol
> __FOO_BEGIN__ in an object file _at the beginning of your link command_
> in that same section, and __FOO_END__ in an object file at the end.
Gasp. I am still trying hard to understand what's going on in
crtstuff.c...
> I don't understand at all why CLN is jumping through these hoops. It
> looks like it could just create global objects, and piggyback on GCC's
> constructor mechanism. What on earth is it trying to accomplish?
To get the calling order right. CLN consists of >800 source-code modules
and uses a bridge pattern to abstract the actual implementation away from
the interface.
The code I submitted was expanded from a macro called CL_PROVIDE(foo).
This is put as a marker into the source file where the static object we
want to have initialized is sitting in. Then, CL_REQUIRE(foo) is put into
the header file where that object is declared extern.
This comment is lifted from file ${prefix}/include/cln/modules.h:
// The order of initialization of different compilation units is not
// specified in C++. AIX 4 has a linker which apparently does order
// the modules according to dependencies, so that low-level modules
// will be initialized earlier than the high-level modules which depend
// on them. I have a patch for GNU ld that does the same thing.
//
// But for now, I take a half-automatic approach to the correct module
// ordering problem: PROVIDE/REQUIRE, as in Common Lisp.
//
// CL_PROVIDE(module) must be the first code-generating entity in a module.
// Inline function definitions can precede it, but global variable/function/
// class definitions may not precede it.
// Afterwards, any number of CL_REQUIRE(othermodule) is allowed.
// At the end of the module, there must be a corresponding
// CL_PROVIDE_END(module). (Sorry for this, it's really needed.)
//
// These macros work only with g++, and only in optimizing mode. But who
// wants to use CLN with other C++ compilers anyway...
Regards
-richy.
--
.''`. Richard B. Kreckel
: :' : <kreckel@debian.org>
`. `' <kreckel@ginac.de>
`- <http://www.ginac.de/~kreckel/>
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