i386ex question

[ian at airs.com (Ian Lance Taylor)]

   Date: Wed, 30 Sep 1998 13:51:00 -0500 (CDT)
   From: <joel at OARcorp.com>

   On 29 Sep 1998 ian at airs.com wrote:

   > I'm not completely up on i386 details, but my impression is that the
   > instruction you really want here is
   >     data32 addr32 lgdt gdtptr - start16
   > 
   > An autoconf test to see whether this works is
   > 
   > AC_TRY_COMPILE(,[asm(".code16; data32 addr32 lgdt 0; .code32");],
   >   AC_DEFINE(NEW_GAS))

   What does this need to be wrapped in to insure that it is only used on
   i386-rtems* targets?

Something along these lines would probably do the job.  However, I
don't know the best way to communicate the result of the test to the
code in question.

In this patch I called AC_DEFINE; that will only work if an
appropriate entry is added to c/build-tools/src/config.h.in, and if
the assembler code includes that file.

Another, probably better, approach would be to call AC_SUBST, and then
to have the appropriate Makefile pass the information when it
assembles the file.  I don't really grok the RTEMS Makefile setup.

Ian

Index: configure.in
===================================================================
RCS file: /zembu/cvsfiles/devo/rtems/configure.in,v
retrieving revision 1.1.1.3
diff -u -r1.1.1.3 configure.in
--- configure.in	1998/09/29 22:16:50	1.1.1.3
+++ configure.in	1998/09/30 19:08:37
@@ -227,6 +227,24 @@
 
 RTEMS_CANONICALIZE_TOOLS
 
+dnl check for i386 gas supporting 16 bit mode
+if test "${target_cpu}" = "i386"; then
+  AC_CACHE_CHECK([for 16 bit mode assembler support],
+    rtems_cv_prog_gas_code16,
+    [cat > conftest.s << EOF
+	.code16
+	data32 addr32 lgdt 0
+EOF
+    if AC_TRY_COMMAND($AS_FOR_TARGET -o conftest.o conftest.s); then
+      rtems_cv_prog_gas_code16=yes
+    else
+      rtems_cv_prog_gas_code16=no
+    fi])
+  if test "$rtems_cv_prog_gas_code16" = "yes"; then
+    AC_DEFINE(RTEMS_PROG_GAS_CODE16)
+  fi
+fi
+
 dnl check host cc
 AC_PROG_CC