[Gc] Dependency tracking for configuration macros

Petter Urkedal urkedal at nbi.dk
Wed May 20 13:29:58 PDT 2009

On 2009-05-20, Ivan Maidanski wrote:
> Petter Urkedal <urkedal at nbi.dk> wrote:
> > The attached patch adds AC_CONFIG_HEADER to configure.ac, so that the
> > command-line "-D"-options are replace by the conditional inclusion of a
> > generated config.h header.  The major part of the patch is the addition
> > of documentation to configuration macros.
> Opinion:
> 1. instead of inclusion of "gc_config_macros.h" from misc .c files (like backgraph.c one), I'd rather include "gc.h" - see my patch in https://permalink.gmane.org/gmane.comp.programming.garbage-collection.boehmgc/2575 (mostly taken from GCC/boehm-gc).

Yes, I don't mind that.  If that patch is to be committed, I could wait
and rebase my changes.  (Hans?)

> 2. Inclusion of a "private/..." file from a public header ("gc_config_macros.h") is not a good idea (even if it is ifdef'ed), I think.

I principal I agree, but the problem is that "gc.h" includes
"gc_version.h", and the latter file must be included after the Autoconf
macros, if they are to be included.  This is the reason I felt it
necessary to add GC_PRIVATE_CONFIG_H as a supplement to the standard
CONFIG_H definition.  I consider the ifdef-guard safe since
GC_PRIVATE_CONFIG_H is in the "namespace" of the collector, but granted,
it looks a bit ugly to an end-user who reads the include file.

On a related note, it might also be of interest to make configuration
macros available from public headers.  In my own code I usually
transform the config.h by adding a project-specific prefix to all macros
which do not already start with said prefix.

> > I tested the patch on various configurations on Linux x86_64 and i386 by
> > diff-ing the disassembly of the object files before and after applying
> > the patch.
> > 
> > -----%<-----
> > Dependency tracking for configuration macros.
> > 
> > configure.ac, acinclude.m4:
> >         * Invoke AC_CONFIG_HEADER.
> >         * Added documentation of configuration macros.
> >         * Commented out the unused macros STACKBASE and DATASTART_IS_ETEXT.
> STACKBASE should be also removed in misc.c file.

Yes, I was puzzled by that lone #undef...

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