[bug #36186] gnustep-make fails to detect that clang supports native objective-c exceptions with --enable-objc-nonfragile-abi

[Chris Armstrong]

URL:
  <http://savannah.gnu.org/bugs/?36186>

                 Summary: gnustep-make fails to detect that clang supports
native objective-c exceptions with --enable-objc-nonfragile-abi
                 Project: GNUstep
            Submitted by: carmstrong
            Submitted on: Sun 15 Apr 2012 06:41:54 AM GMT
                Category: Makefiles
                Severity: 3 - Normal
              Item Group: Bug
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any

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Details:

I'm using clang to compile gnustep. However, gnustep-make is failing to detect
that clang supports native objective-c exceptions (this is causing me a world
of pain in other libraries) when the non-fragile abi flag is enabled. It works
correctly when the non-fragile abi flag is not specified.

I've discovered this is because of a failure in the conftest used to detect
native objective-c exceptions. When it attempts to compile it, it fails with
the following error (config.log attached for reference):

CC=clang 
./configure
==>
configure:5752: checking whether the compiler supports native ObjC exceptions
configure:5780: clang -c  -fexceptions -fobjc-exceptions  conftest.c >&5
clang: warning: argument unused during compilation: '-fobjc-exceptions'
conftest.c:11:1: error: expected identifier or '('
@interface Test { id isa; } @end
^
1 error generated.
configure:5780: $? = 1
<===

It must have something to do with the redefinition of CFLAGS in the
non-fragile if/fi block, as the "-x objective-c" flag is not getting to the
compiler for this conftest.

I suspect its related to the following code in configure.ac:
=====
AC_MSG_CHECKING(whether we should use the nonfragile ABI)
if test x"$USE_NONFRAGILE_ABI" = x"yes"; then
  # What we want to do: set USE_NONFRAGILE_ABI to yes if we can compile
  # something with -fobjc-nonfragile-abi.
  CFLAGS_nonfragile="$CFLAGS"
  CFLAGS="$CFLAGS -fobjc-nonfragile-abi"
  AC_COMPILE_IFELSE([[
/* Note that we never execute this code so it does not really matter
   what it is.  We are testing that the compiler accepts the
   '-fobjc-nonfragile-abi' flag.  */
int   
main()
{   
#ifndef __has_feature
#define __has_feature(x) 0
#endif
return __has_feature(objc_nonfragile_abi) ? 0 : 1;
}
]], USE_NONFRAGILE_ABI=yes, USE_NONFRAGILE_ABI=no)
  AC_MSG_RESULT($USE_NONFRAGILE_ABI)
  CFLAGS="$CFLAGS_no_nonfragile"

  if test x$USE_NONFRAGILE_ABI = xno; then
    AC_MSG_NOTICE([The nonfragile ABI was requested, but the compiler])
    AC_MSG_NOTICE([doesn't support it.])
    AC_MSG_ERROR([compiler doesn't support nonfragile ABI])
  fi
else
  AC_MSG_RESULT(not requested by user)
fi

AC_SUBST(USE_NONFRAGILE_ABI)
======

Notice how we define CFLAGS_nonfragile, but we then set:
CFLAGS=$CFLAGS_no_nonfragile

I think this is causing the problem. I was able to fix it by changing that
line to read:
CFLAGS="$CFLAGS_nonfragile"

I don't know why there is a reference to a CFLAGS_no_nonfragile; the configure
script aborts if the non-fragile ABI is requested but not supported.

Can anyone else shed light on this? 



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File Attachments:


-------------------------------------------------------
Date: Sun 15 Apr 2012 06:41:54 AM GMT  Name: config.log  Size: 25kB   By:
carmstrong
config.log generated from &quot;export CC=clang; ./configure
--enable-objc-nonfragile-abi&quot;
<http://savannah.gnu.org/bugs/download.php?file_id=25649>

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