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To: "cygwin@cygwin.com" <cygwin@cygwin.com>
Subject: stack grow direction wrongly detected
Message-ID: <6eded5d3-93f3-7c98-5055-ee5ac2566bc8@gmail.com>
Date: Fri, 5 Mar 2021 13:18:38 +0100
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From: Marco Atzeri via Cygwin <cygwin@cygwin.com>
Reply-To: Marco Atzeri <marco.atzeri@gmail.com>
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Sender: "Cygwin" <cygwin-bounces@cygwin.com>

Hi Guys,
noted trying to rebuild guile 1.8.8.

The following piece of code in the past
was setting SCM_I_GSC_STACK_GROWS_UP=0
and now produces SCM_I_GSC_STACK_GROWS_UP=1

I assume some change in the gcc compiler is causing the issue.
I presume most of the programs and libraries do not care,
but some special one like guile crashes during build for this issue,
so be aware.

Regards
Marco


#--------------------------------------------------------------------
#
# Which way does the stack grow?
#
# Following code comes from Autoconf 2.61's internal _AC_LIBOBJ_ALLOCA
# macro (/usr/share/autoconf/autoconf/functions.m4).  Gnulib has
# very similar code, so in future we could look at using that.
#
# An important detail is that the code involves find_stack_direction
# calling _itself_ - which means that find_stack_direction (or at
# least the second find_stack_direction() call) cannot be inlined.
# If the code could be inlined, that might cause the test to give
# an incorrect answer.
#--------------------------------------------------------------------

SCM_I_GSC_STACK_GROWS_UP=0
AC_RUN_IFELSE([AC_LANG_SOURCE(
[AC_INCLUDES_DEFAULT
int
find_stack_direction ()
{
   static char *addr = 0;
   auto char dummy;
   if (addr == 0)
     {
       addr = &dummy;
       return find_stack_direction ();
     }
   else
     return (&dummy > addr) ? 1 : -1;
}

int
main ()
{
   return find_stack_direction () < 0;
}])],
                [SCM_I_GSC_STACK_GROWS_UP=1],
                [],
                [AC_MSG_WARN(Guessing that stack grows down -- see 
scmconfig.h)])

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