[New-bugs-announce] [issue8211] configure: ignore AC_PROG_CC hardcoded CFLAGS

[STINNER Victor]

New submission from STINNER Victor <victor.stinner at haypocalc.com>:

configure.in uses AC_PROG_CC, extract of the autoconf manual:
(http://www.delorie.com/gnu/docs/autoconf/autoconf_64.html)
 
 If using the GNU C compiler, set shell variable GCC to `yes'. If output variable CFLAGS was not already set, set it to `-g -O2' for the GNU C compiler (`-O2' on systems where GCC does not accept `-g'), or `-g' for other compilers.

Python does already set the optimization level in its OPT variable: for gcc, it uses -O3 by default, and not -O option (in this case, gcc disables all optimisations, it's like -O0) if --with-pydebug is used.

Because of AC_PROG_CC, Python is compiled with -O2 even if --with-pydebug is used, which is bad because it's harder to debug an optimized program: most variable are unavailable (gcc prints "<optimized out>").

Another problem is that AC_PROG_CC eats user CFLAGS. It's not possible to specify: ./configure CFLAGS="myflags".

On the autoconf mailing list, I saw a simple "trick": 

   Save CFLAGS before you call AC_PROG_CC, and restore it after, 
   if you don't want "-g -O2".

Attached patch implements that. Results:
 * ./configure: CFLAGS=$(BASECFLAGS) $(OPT) $(EXTRA_CFLAGS)
 * ./configure --with-pdebug CFLAGS="-O0": CFLAGS=$(BASECFLAGS) -O0 $(OPT) $(EXTRA_CFLAGS)

It works :-)

----------
components: Build
files: configure_cflags.patch
keywords: patch
messages: 101578
nosy: haypo
severity: normal
status: open
title: configure: ignore AC_PROG_CC hardcoded CFLAGS
versions: Python 2.6, Python 2.7, Python 3.1, Python 3.2
Added file: http://bugs.python.org/file16628/configure_cflags.patch

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