i386: Fail at configure time for i386 builds.

This change does two things:

* Treats a target i386-* as if it were i686.
* Fails configure if the user is generating code
  for i386.

We no longer support i386 code-generation because the i386
lacks the atomic operations we need in glibc.

You can still configure for i386-*, but you get i686 code.

You can't build with --march=i386, --mtune=i386 or a compiler
that defaults to i386 code-generation.

I've added two i386 entries in the master todo list to discuss
merging and renaming:
http://sourceware.org/glibc/wiki/Development_Todo/Master#i386

The failure modes are fail-safe here. You compile for i386,
get i686, and try to run on i386 and it fails. The configure
log has a warning saying we elided to i686. There is no situation
that I can see where we run into any serious problems.

The patch makes the current state better in that we get less
confused users and we build successfully in more default
configurations.

The next enhancement would be to add --march=i?86
as suggested in #c20 of BZ#10062 for any i?86-* builds, which
would solve the problem of a 32-bit compiler that defaults to
i386 code-gen and glibc configured for i686-* target. Which
previously failed at build time, and now will fail at configure
time (requires adding --march=i686).

Updated NEWS with BZ #10060 and #10062.

No regressions.

---

2013-04-06  Carlos O'Donell  <carlos@redhat.com>

	[BZ #10060, #10062]
	* aclocal.m4 (LIBC_COMPILER_BUILTIN_INLINED): New macro.
	* sysdeps/i386/configure.in: Use LIBC_COMPILER_BUILTIN_INLINED and
	fail configure if __sync_val_compare_and_swap is not inlined.
	* sysdeps/i386/configure: Regenerate.
	* configure.in: Build for i686 when configured for i386.
	* configure: Regenerate.
	* README: Remove i386 reference.

2 files changed, 58 insertions, 0 deletions

diff --git a/sysdeps/i386/configure b/sysdeps/i386/configure
index d81b613a..a1a0fe7 100644
--- a/sysdeps/i386/configure
+++ b/sysdeps/i386/configure
@@ -32,6 +32,45 @@ $as_echo "$ac_res" >&6; }
 # This file is generated from configure.in by Autoconf.  DO NOT EDIT!
  # Local configure fragment for sysdeps/i386.
 
+# The GNU C Library can't be built for i386.  There are several reasons for
+# this restriction.  The primary reason is that i386 lacks the atomic
+# operations required to support the current NPTL implementation.  While it is
+# possible that such atomic operations could be emulated in the kernel to date
+# no such work has been done to enable this.  Even with NPTL disabled you still
+# have no atomic.h implementation.  Given the declining use of i386 we disable
+# support for building with `-march=i386' or `-mcpu=i386.' We don't explicitly
+# check for i386, instead we make sure the compiler has support for inlining
+# the builtin __sync_val_compare_and_swap. If it does then we should have no
+# problem building for i386.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for compiler support of inlined builtin function __sync_val_compare_and_swap" >&5
+$as_echo_n "checking for compiler support of inlined builtin function __sync_val_compare_and_swap... " >&6; }
+libc_compiler_builtin_inlined=no
+cat > conftest.c <<EOF
+int _start (void) { int a, b, c; __sync_val_compare_and_swap (&a, b, c); return 0; }
+EOF
+if ! { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS
+		     -O0 -nostdlib -nostartfiles
+		     -S conftest.c -o - | fgrep "__sync_val_compare_and_swap"
+		     1>&5'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }
+then
+  libc_compiler_builtin_inlined=yes
+fi
+rm -f conftest*
+if test $libc_compiler_builtin_inlined = yes; then
+  libc_cv_unsupported_i386=no
+else
+  as_fn_error $? "
+*** Building with -march=i386/-mcpu=i386 is not supported.
+*** Please use host i786, i686, i586, or i486." "$LINENO" 5
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_compiler_builtin_inlined" >&5
+$as_echo "$libc_compiler_builtin_inlined" >&6; }
+
 
 ac_fn_c_check_header_compile "$LINENO" "cpuid.h" "ac_cv_header_cpuid_h" "/* No default includes.  */
 "
diff --git a/sysdeps/i386/configure.in b/sysdeps/i386/configure.in
index 9967a16..56a7c1f 100644
--- a/sysdeps/i386/configure.in
+++ b/sysdeps/i386/configure.in
@@ -1,6 +1,25 @@
 GLIBC_PROVIDES dnl See aclocal.m4 in the top level source directory.
 # Local configure fragment for sysdeps/i386.
 
+# The GNU C Library can't be built for i386.  There are several reasons for
+# this restriction.  The primary reason is that i386 lacks the atomic
+# operations required to support the current NPTL implementation.  While it is
+# possible that such atomic operations could be emulated in the kernel to date
+# no such work has been done to enable this.  Even with NPTL disabled you still
+# have no atomic.h implementation.  Given the declining use of i386 we disable
+# support for building with `-march=i386' or `-mcpu=i386.' We don't explicitly
+# check for i386, instead we make sure the compiler has support for inlining
+# the builtin __sync_val_compare_and_swap. If it does then we should have no
+# problem building for i386.
+LIBC_COMPILER_BUILTIN_INLINED(
+  [__sync_val_compare_and_swap],
+  [int a, b, c; __sync_val_compare_and_swap (&a, b, c);],
+  [-O0],
+  [libc_cv_unsupported_i386=no],
+  [AC_MSG_ERROR([
+*** Building with -march=i386/-mcpu=i386 is not supported.
+*** Please use host i786, i686, i586, or i486.])])
+
 AC_CHECK_HEADER([cpuid.h], ,
   [AC_MSG_ERROR([gcc must provide the <cpuid.h> header])],
   [/* No default includes.  */])