[glibc/gabriel/powerpc-ieee128-printscan] powerpc64le: Require a compiler with -mno-gnu-attribute

[Gabriel F.T.Gomes <gftg@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=b843c8d832cdb2a1000b45e853c17211de67b4e7

commit b843c8d832cdb2a1000b45e853c17211de67b4e7
Author: Gabriel F. T. Gomes <gabrielftg@linux.ibm.com>
Date:   Fri Oct 11 15:20:05 2019 -0300

    powerpc64le: Require a compiler with -mno-gnu-attribute
    
    On powerpc64le, a few files are built on IEEE long double mode
    (-mabi=ieeelongdouble), whereas most are built on IBM long double mode
    (-mabi=ibmlongdouble, the default for -mlong-double-128). Since binutils
    2.31, linking object files with different long double modes causes
    errors similar to:
    
      ld: libc_pic.a(s_isinfl.os) uses IBM long double,
          libc_pic.a(ieee128-qefgcvt.os) uses IEEE long double.
      collect2: error: ld returned 1 exit status
      make[2]: *** [../Makerules:649: libc_pic.os] Error 1
    
    The warnings are fair and correct, but in order for glibc to have
    support for both long double modes on powerpc64le, they have to be
    ignored.  This can be accomplished with the use of -mno-gnu-attribute
    option when building the few files that require IEEE long double mode.
    
    However, -mno-gnu-attribute is not available in GCC 6, the minimum
    version required to build glibc, so this patch adds a test for this
    feature in powerpc64le builds, and fails early if it's not available.
    
    Tested, on powerpc64le, that the build fails early with GCC 6 and that
    it succeeds with GCC 7 or greater.

Diff:
---
 sysdeps/powerpc/powerpc64/le/configure    | 29 +++++++++++++++++++++++++++++
 sysdeps/powerpc/powerpc64/le/configure.ac | 15 +++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/sysdeps/powerpc/powerpc64/le/configure b/sysdeps/powerpc/powerpc64/le/configure
index bca80ce..c8e01af 100644
--- a/sysdeps/powerpc/powerpc64/le/configure
+++ b/sysdeps/powerpc/powerpc64/le/configure
@@ -32,4 +32,33 @@ if test "$libc_cv_target_power8_ok" != "yes"; then :
 fi
 CFLAGS="$OLD_CFLAGS"
 
+# Local configure fragment for sysdeps/powerpc/powerpc64le.
+
+OLD_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -mno-gnu-attribute"
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking if the compiler supports -mno-gnu-attribute" >&5
+$as_echo_n "checking if the compiler supports -mno-gnu-attribute... " >&6; }
+if ${libc_cv_no_gnu_attr_ok+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  libc_cv_no_gnu_attr_ok=yes
+else
+  libc_cv_no_gnu_attr_ok=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_no_gnu_attr_ok" >&5
+$as_echo "$libc_cv_no_gnu_attr_ok" >&6; }
+if test "$libc_cv_no_gnu_attr_ok" != "yes"; then :
+  critic_missing="$critic_missing A compiler with -mno-gnu-attribute is required on powerpc64le."
+fi
+CFLAGS="$OLD_CFLAGS"
+
 test -n "$critic_missing" && as_fn_error $? "*** $critic_missing" "$LINENO" 5
diff --git a/sysdeps/powerpc/powerpc64/le/configure.ac b/sysdeps/powerpc/powerpc64/le/configure.ac
index 7f2c9fb..fdec696 100644
--- a/sysdeps/powerpc/powerpc64/le/configure.ac
+++ b/sysdeps/powerpc/powerpc64/le/configure.ac
@@ -17,4 +17,19 @@ AS_IF([test "$libc_cv_target_power8_ok" != "yes"],
       [critic_missing="$critic_missing POWER8 or newer is required on powerpc64le."])
 CFLAGS="$OLD_CFLAGS"
 
+# Local configure fragment for sysdeps/powerpc/powerpc64le.
+
+dnl Require support for -mno-gnu-attribute
+OLD_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -mno-gnu-attribute"
+AC_CACHE_CHECK([if the compiler supports -mno-gnu-attribute],
+	       libc_cv_no_gnu_attr_ok, [
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+]])],
+	       [libc_cv_no_gnu_attr_ok=yes],
+	       [libc_cv_no_gnu_attr_ok=no])])
+AS_IF([test "$libc_cv_no_gnu_attr_ok" != "yes"],
+      [critic_missing="$critic_missing A compiler with -mno-gnu-attribute is required on powerpc64le."])
+CFLAGS="$OLD_CFLAGS"
+
 test -n "$critic_missing" && AC_MSG_ERROR([*** $critic_missing])