On Sun, Sep 07, 2003 at 02:07:51PM -0400, Daniel Jacobowitz wrote: > Hi autoconf'ers... > > I've been involved in converting a number of projects in the GCC and sources > (binutils, gdb, etc) repositories to autoconf 2.57. By and large, it's > going well, but we've turned up a couple of problems. I'm not familiar with > autoconf development, so these may have more historical baggage than I know > about... > > The first is with AC_CHECK_HEADERS. The manual says: > Previous versions of Autoconf merely checked whether the header was > accepted by the preprocessor. This was changed because the old test was > inappropriate for typical uses. Headers are typically used to compile, > not merely to preprocess, and the old behavior sometimes accepted > headers that clashed at compile-time. > > However, that's not the whole story. The old check also failed if there > were warning messages on stderr when preprocessing. The new one doesn't do > that, by default. Instead it only does so if ac_c_preproc_warn_flag, which > is only set if missing headers are a warning rather than an error. As a > result autoconf now decides malloc.h is available on FreeBSD, even though it > has a #warning in it. > > Test case: > foo.h: > #warning "A.h" > > configure.in: > AC_INIT(foo.h) > AC_CHECK_HEADERS([foo.h]) > AC_OUTPUT > > Old output: > configure:609: checking for foo.h > configure:619: gcc -I/home/drow/autoconf/o/.. -E conftest.c >/dev/null 2>conftest.out > In file included from configure:615: > /home/drow/autoconf/foo.h:1:2: warning: #warning "A.h" > configure: failed program was: > #line 614 "configure" > #include "confdefs.h" > #include <foo.h> > > > configure:2606: checking foo.h usability > configure:2619: gcc -I/home/drow/autoconf/o/.. -c -g -O2 conftest.c >&5 > In file included from configure:2660: /home/drow/autoconf/foo.h:1:2: warning: #warning "A.h" > configure:2622: $? = 0 > configure:2625: test -s conftest.o > configure:2628: $? = 0 > configure:2638: result: yes > configure:2642: checking foo.h presence > configure:2653: gcc -I/home/drow/autoconf/o/.. -E conftest.c > In file included from configure:2662: /home/drow/autoconf/foo.h:1:2: warning: #warning "A.h" > configure:2659: $? = 0 > configure:2678: result: yes > configure:2714: checking for foo.h > configure:2721: result: yes Any comments on this? I can work around it by conditionally putting -Werror into CPPFLAGS, but I don't really like that; I'm not sure what else it might do to configure. Both compiler warnings and errors used to be fatal and now neither of them seem to be. -- Daniel Jacobowitz MontaVista Software Debian GNU/Linux Developer
