[RFC] want to #undef HAVE_SBRK and HAVE_POLL on Interix

[Joel Brobecker <brobecker@gnat.com>]

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Hello,

This is something I did sometime ago, and wanted to discuss with you
before proposing a change more formally. 

Here goes: On Interix, the sbrk() function exists, but is not
sufficiently implemented to be used in GDB. Because it exists,
AC_CHECK_FUNCS (sbrk) finds it, and therefore configure adds the
associated "#define HAVE_SBRK" in config.h.

If you look at xm-interix.h in the files I recently submitted, you will
see that there is a "#undef HAVE_SBRK" to counter the result of
AC_CHECK_FUNCS. I would like to get rid of this #undef. To do that, the
only way I found is to either:
  1. let configure test for sbrk() on Interix, but then override the
     test result afterward by undefining (in the configure sense)
     HAVE_SBRK. Something like:

     AC_CHECK_FUNCS (....)     # this line is unchanged
     case "${host}" in
       *-*-interix* )
         undefine (HAVE_BRK)
         ;;
       * )
         ;;
     esac
     
  2. do not do the AC_CHECK_FUNCS test for sbrk() on Interix. This way,
     HAVE_SBRK will never be defined, and we don't need the undef in
     xm-interix.h anymore.

I did not find a way in the documentation to undefine a variable that
was previously defined. So I could not implement 1. I also thought that
a user might find it confusing to see the output of configure show

     Checking for sbrk... yes

and then no see HAVE_SBRK defined in config.h...
     
So I implemented 2. A patch is attached (it is only the configure.in
part, the rest will follow if the approach to the problem is approved).
I also did the same for the poll() function, which should not be used
on Interix as well.

Is it the best approach to the problem? Would such a patch be accepted
for inclusion?

Thanks,
-- 
Joel

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Index: configure.in
===================================================================
RCS file: /cvs/src/src/gdb/configure.in,v
retrieving revision 1.91
diff -c -3 -p -r1.91 configure.in
*** configure.in	20 Sep 2002 00:24:01 -0000	1.91
--- configure.in	21 Oct 2002 05:52:28 -0000
*************** AC_HEADER_STAT
*** 134,141 ****
  AC_C_CONST
  AC_C_INLINE
  
! AC_CHECK_FUNCS(bcopy btowc bzero canonicalize_file_name isascii poll \
! 	realpath sbrk setpgid setpgrp sigaction sigprocmask sigsetmask )
  AC_FUNC_ALLOCA
  AC_FUNC_VFORK
  dnl AC_FUNC_SETPGRP does not work when cross compiling
--- 134,161 ----
  AC_C_CONST
  AC_C_INLINE
  
! AC_CHECK_FUNCS(bcopy btowc bzero canonicalize_file_name isascii \
! 	realpath setpgid setpgrp sigaction sigprocmask sigsetmask )
! 
! # Certain systems implement broken or incomplete versions of some
! # functions, which cause AC_CHECK_FUNCS to define the associated HAVE_*
! # macro.  But we actually do not want to this macro to be defined on
! # these systems where we know it is broken. So we simply skip the test
! # for these functions and pretend that it does not exist.
! case "${host}" in
!   *-*-interix*) 
!     # On Interix, there is only a minimal sbrk(). This function does not
!     # provide the functionality that is needed in the case of GDB (there
!     # is no relationship at all with environ). 
! 
!     # The poll() function is only partially implemented so far...
!     ;;
!   *)
!     AC_CHECK_FUNCS(sbrk)
!     AC_CHECK_FUNCS(poll)
!     ;;
! esac
! 
  AC_FUNC_ALLOCA
  AC_FUNC_VFORK
  dnl AC_FUNC_SETPGRP does not work when cross compiling