Re: AM_CFLAGS not included in translation unit compilation

[Mike Mattie]

On 12/12/05, Ralf Wildenhues <address@hidden> wrote:
> Hi Mike,
>
> * Mike Mattie wrote on Sat, Dec 10, 2005 at 07:24:35PM CET:
> > On 12/8/05, Ralf Wildenhues <address@hidden> wrote:
> > > * Mike Mattie wrote on Fri, Dec 09, 2005 at 12:59:33AM CET:
> > > >
> > > > In a recent project I noticed that the individual compilation units do
> > > > not include AM_CFLAGS in the invocation of the compiler, however
> > > > when the program is constructed in the linking phase the AM_CFLAGS
> > > > variable is used. Is there a rational for this ? I would like
> > > > to place debugging (-g) in AM_CFLAGS and instead I am placing it in 
> > > > prog_CFLAGS.
> > >
> > > Does reading this chapter of the documentation answer your question?
> > > http://sources.redhat.com/automake/automake.html#Flag-Variables-Ordering
> >
> > actually it makes me think even more that my automake (1.9.6) has a
> > regression against the behavior of previous releases and the
> > documentation.
>
> Depends.  I would call it a bugfix rather than a regression.
> But let's be precise here.  Here's a cooked-down version of your issue:
>
> touch foo.c bar.c
> cat >configure.ac <<EOF
> AC_INIT
> AM_INIT_AUTOMAKE([foo], [0.1])
> AC_PROG_CC
> AM_PROG_CC_C_O
> AC_CONFIG_FILES([Makefile])
> AC_OUTPUT
> EOF
> cat >Makefile.am <<EOF
> AM_CFLAGS = -amcflags
> bin_PROGRAMS = foo bar
> foo_CFLAGS = -foocflags
> EOF
> aclocal
> automake -a --foreign
> autoconf
> grep -C2 CFLAGS Makefile.in
>
> For different Automake versions, the following happens:
> 1.4:  no use of foo_CFLAGS at all.
>
> 1.5:  foo_CFLAGS are used for compiling foo.c, but not for linking
>       AM_CFLAGS used for compiling bar.c, and for linking both.
>
> Ditto for everything up to 1.9.6 (I believe).
>
> 1.9a: AM_CFLAGS used for compiling and linking bar,
>       foo_CFLAGS used for compiling and linking foo.
>
> Never are foo_CFLAGS and AM_CFLAGS used *both* on the same command line.
> This corresponds to the fact that with many compilers, compilation flags
> are not easily overridable, and the primary intended use of foo_CFLAGS
> was to give the developer a way to override AM_CFLAGS (I think).
>
> > AM_CFLAGS is clearly missing. however AM_CFLAGS is referanced when
> > server.o is linked from sever-server.o
>
> I don't think server.o would ever be used to create sever-server.o.
> Automake never issues incremental linking rules itself.  Maybe you
> meant
>   server is linked from sever-server.o
> ?
>
> > I think this is clearly wrong. I have a older autotools project from
> > 2003 where I clearly relied on compiler flags for translation units
> > being referenced from AM_CFLAGS across the entire
> > project.
>
> Well, I don't see any automake version where it would have worked this
> way, in that AM_CFLAGS would have been used during compilation.  Except
> for when foo_CFLAGS wasn't supported at all.
>
> > If I wished to include flags at the link phase only I would choose
> > _LDFLAGS after reading the documentation.
>
> Yes.  AM_CFLAGS and AM_LDFLAGS clearly do have different use though.
>
> > I think the above demonstrates that it is not a ordering issue, rather
> > that a variable that should be included in a compilation is missing
> > altogether.
>
> Do you still think this?
>
> > What I need to know is will the upstream maintainers call this one as a bug 
> > ?
>
> Can't answer that, but I still don't see the way it regresses.  Sorry.
>
> Cheers,
> Ralf
>

I am following now, foo_CFLAGS blows away AM_CFLAGS . thanks for the
help in understanding this. I will simply reference AM_CFLAGS in
foo_CFLAGS when I want to
combine the two.

thanks again for helping me understand this.