[PATCH v2 29/30] powerpc64le: Require a compiler with -mno-gnu-attribute

["Gabriel F. T. Gomes" <gabriel@inconstante.net.br>]

From: "Gabriel F. T. Gomes" <gabrielftg@linux.ibm.com>

Changes since v1:

  - Added mentions to the build requirement in manual/install.texi,
    INSTALL (regenerated) and NEWS.

-- 8< --
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.
---
 INSTALL                                   |  5 ++++
 NEWS                                      |  2 +-
 manual/install.texi                       |  5 ++++
 sysdeps/powerpc/powerpc64/le/configure    | 29 +++++++++++++++++++++++
 sysdeps/powerpc/powerpc64/le/configure.ac | 15 ++++++++++++
 5 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/INSTALL b/INSTALL
index 392537cc5c..1baa99f304 100644
--- a/INSTALL
+++ b/INSTALL
@@ -467,6 +467,11 @@ build the GNU C Library:
      better code.  As of release time, GCC 9.1.1 is the newest compiler
      verified to work to build the GNU C Library.
 
+     For PowerPC 64-bits little-endian (powerpc64le), a GCC version with
+     support for -mno-gnu-attribute is required.  As of release time,
+     this means GCC 7 or higher.  The compiler option is required for
+     building the GNU C Library with support for IEEE long double.
+
      For multi-arch support it is recommended to use a GCC which has
      been built with support for GNU indirect functions.  This ensures
      that correct debugging information is generated for functions
diff --git a/NEWS b/NEWS
index d7286841c9..7fb3727ab0 100644
--- a/NEWS
+++ b/NEWS
@@ -32,7 +32,7 @@ Deprecated and removed features, and other changes affecting compatibility:
 
 Changes to build and runtime requirements:
 
-  [Add changes to build and runtime requirements here]
+* On powerpc64le, GCC 7 or later is required to build the GNU C Library.
 
 Security related changes:
 
diff --git a/manual/install.texi b/manual/install.texi
index b2d569ac5a..85767ebde3 100644
--- a/manual/install.texi
+++ b/manual/install.texi
@@ -507,6 +507,11 @@ the newest version of the compiler that is known to work for building
 release time, GCC 9.1.1 is the newest compiler verified to work to build
 @theglibc{}.
 
+For PowerPC 64-bits little-endian (powerpc64le), a GCC version with
+support for -mno-gnu-attribute is required.  As of release time, this
+means GCC 7 or higher. The compiler option is required for building the
+GNU C Library with support for IEEE long double.
+
 For multi-arch support it is recommended to use a GCC which has been built with
 support for GNU indirect functions.  This ensures that correct debugging
 information is generated for functions selected by IFUNC resolvers.  This
diff --git a/sysdeps/powerpc/powerpc64/le/configure b/sysdeps/powerpc/powerpc64/le/configure
index bca80cec76..c8e01af4f2 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 7f2c9fbf1f..fdec69603b 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])
-- 
2.21.0