Re: Question about CFLAGS

[Bob Friesenhahn]

On Wed, 16 Apr 2008, Sérgio Durigan Júnior wrote:
> > In general a configure script should never modify CFLAGS.  But flags
> > like -m64 that select a completely different ABI should better be put in
> > CC, not CFLAGS.

I will second the above statement.

> Does that mean that CFLAGS is a variable only for the user? Well, let's
> say that, for some strong reason, the configure is actually modifying
> it. What would be the correct behaviour in this case? FYI, I'm talking
> specifically about Python's build system, which uses 3 internal
> variables ($BASECFLAGS, $OPT and $EXTRA_CFLAGS), but strangely ignores
> the value of CFLAGS provided by the user. It's causing some troubles,
> and we're trying to fix it. More information can be found at
> http://bugs.python.org/issue1628484 .

That would seem to be a bug in Python's configure script.  When it 
comes to the variables listed at the tail of configure's --help 
output:

Some influential environment variables:
  CC          C compiler command
  CFLAGS      C compiler flags
  LDFLAGS     linker flags, e.g. -L<lib dir> if you have libraries in a
              nonstandard directory <lib dir>
  LIBS        libraries to pass to the linker, e.g. -l<library>
  CPPFLAGS    C/C++/Objective C preprocessor flags, e.g. -I<include dir> if
              you have headers in a nonstandard directory <include dir>
  CPP         C preprocessor
  CXX         C++ compiler command
  CXXFLAGS    C++ compiler flags
  CXXCPP      C++ preprocessor
  F77         Fortran 77 compiler command
  FFLAGS      Fortran 77 compiler flags
  FC          Fortran compiler command
  FCFLAGS     Fortran compiler flags

user provided options should always be treated with respect and should 
be honored in such a way that the user provided options will have most 
useful effect.  For example, if you add -I options to CPPFLAGS, then 
the user-provided portion should be prepended so that the user can use 
CPPFLAGS to override a default inclusion.  For CFLAGS, the user 
provided part should likely be appended so that the user can override 
the defaults.

If a package is using Automake, then it is useful to take advantage of 
AM_ prefixed variables in order to taint user-provided input as little 
as possible.

Regardless, I seem to have built a 64-bit version of Python in an 
environment which defaults to 32-bits by defining 'CC' rather than 
'CFLAGS'.

Bob
======================================
Bob Friesenhahn
address@hidden, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/