[glibc] powerpc64le: blacklist broken GCC compilers (e.g GCC 7.5.0)

[glibc] powerpc64le: blacklist broken GCC compilers (e.g GCC 7.5.0)

[Paul E. Murphy]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=5c7ccc29830fb59d39d67222caca5b4bd6ca2e0f

commit 5c7ccc29830fb59d39d67222caca5b4bd6ca2e0f
Author: Paul E. Murphy <murphyp@linux.vnet.ibm.com>
Date:   Tue Mar 17 08:38:54 2020 -0500

    powerpc64le: blacklist broken GCC compilers (e.g GCC 7.5.0)
    
    GCC 7.5.0 (PR94200) will refuse to compile if both -mabi=% and
    -mlong-double-128 are passed on the command line.  Surprisingly,
    it will work happily if the latter is not.  For the sake of
    maintaining status quo, test for and blacklist such compilers.
    
    Tested with a GCC 8.3.1 and GCC 7.5.0 compiler for ppc64le.
    
    Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.ibm.com>

Diff:
---
 INSTALL                                     |  8 +++++---
 manual/install.texi                         | 10 ++++++++--
 sysdeps/ieee754/ldbl-128ibm-compat/Makefile | 12 ------------
 sysdeps/powerpc/powerpc64/le/configure      | 27 +++++++++++++++++++++++++++
 sysdeps/powerpc/powerpc64/le/configure.ac   | 15 +++++++++++++++
 5 files changed, 55 insertions(+), 17 deletions(-)

diff --git a/INSTALL b/INSTALL
index 4bf4bd0908..b7676d1c9f 100644
--- a/INSTALL
+++ b/INSTALL
@@ -469,9 +469,11 @@ build the GNU C Library:
 
      For PowerPC 64-bits little-endian (powerpc64le), a GCC version with
      support for '-mno-gnu-attribute', '-mabi=ieeelongdouble', and
-     '-mabi=ibmlondouble' is required.  These additional features are
-     required for building the GNU C Library with support for IEEE long
-     double.
+     '-mabi=ibmlondouble' is required.  Likewise, the compiler must also
+     support passing '-mlong-double-128' with the preceding options.  As
+     of release, this implies GCC 7.4 and newer (excepting GCC 7.5.0,
+     see GCC PR94200).  These additional features are 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
diff --git a/manual/install.texi b/manual/install.texi
index e801abd8be..f6d9d92317 100644
--- a/manual/install.texi
+++ b/manual/install.texi
@@ -509,8 +509,14 @@ release time, GCC 9.2.1 is the newest compiler verified to work to build
 
 For PowerPC 64-bits little-endian (powerpc64le), a GCC version with support
 for @option{-mno-gnu-attribute}, @option{-mabi=ieeelongdouble}, and
-@option{-mabi=ibmlondouble} is required.  These additional features are
-required for building the GNU C Library with support for IEEE long double.
+@option{-mabi=ibmlondouble} is required.  Likewise, the compiler must also
+support passing @option{-mlong-double-128} with the preceding options.  As
+of release, this implies GCC 7.4 and newer (excepting GCC 7.5.0, see GCC
+PR94200).  These additional features are required for building the GNU C
+Library with support for IEEE long double.
+
+@c powerpc64le performs an autoconf test to verify the compiler compiles with
+@c commands like "$CC -c foo.c -mabi=ibmlongdouble -mlong-double-128".
 
 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
diff --git a/sysdeps/ieee754/ldbl-128ibm-compat/Makefile b/sysdeps/ieee754/ldbl-128ibm-compat/Makefile
index 0ac52a53bc..7b42746c34 100644
--- a/sysdeps/ieee754/ldbl-128ibm-compat/Makefile
+++ b/sysdeps/ieee754/ldbl-128ibm-compat/Makefile
@@ -249,13 +249,6 @@ ldbl-extra-routines += err \
 CFLAGS-ieee128-qefgcvt.c += -mabi=ieeelongdouble -Wno-psabi -mno-gnu-attribute
 CFLAGS-ieee128-qefgcvt_r.c += -mabi=ieeelongdouble -Wno-psabi -mno-gnu-attribute
 
-# Remove -mlong-double-128 because it does not work correctly with
-# -mabi=ibmlongdoule in some GCC versions, e.g. GCC 7.
-$(foreach o,$(all-object-suffixes),$(objpfx)ieee128-qefgcvt$(o)): \
-  sysdep-CFLAGS := $(filter-out -mlong-double-128, $(sysdep-CFLAGS))
-$(foreach o,$(all-object-suffixes),$(objpfx)ieee128-qefgcvt_r$(o)): \
-  sysdep-CFLAGS := $(filter-out -mlong-double-128, $(sysdep-CFLAGS))
-
 tests-internal += tst-ibm128-warn tst-ieee128-warn
 tests-internal += tst-ibm128-error tst-ieee128-error
 tests-internal += tst-ibm128-efgcvt tst-ieee128-efgcvt
@@ -348,11 +341,6 @@ ldbl-ibm128-files := $(objpfx)test-%-ibm128^ \
 		     $(foreach r,$(ldbl-extra-routines),$(objpfx)$(r)-internal^)
 obj-suf-foreach = $(foreach suf,$(all-object-suffixes),$(subst ^,$(suf),$(1)))
 
-# Remove -mlong-double-128 because it does not work correctly with
-# -mabi=ibmlongdoule in some GCC versions, e.g. GCC 7.
-$(call obj-suf-foreach,$(ldbl-ibm128-files)): \
-  sysdep-CFLAGS := $(filter-out -mlong-double-128, $(sysdep-CFLAGS))
-
 # Explicitly add -mabi=ibm-long-double to required files.
 $(call obj-suf-foreach,$(ldbl-ibm128-files)): \
   sysdep-CFLAGS += -mabi=ibmlongdouble
diff --git a/sysdeps/powerpc/powerpc64/le/configure b/sysdeps/powerpc/powerpc64/le/configure
index bd7b8e77d0..98a4889945 100644
--- a/sysdeps/powerpc/powerpc64/le/configure
+++ b/sysdeps/powerpc/powerpc64/le/configure
@@ -90,6 +90,33 @@ if test "$libc_cv_compiler_powerpc64le_ice" != "yes"; then :
   critic_missing="$critic_missing __builtin_signbit is broken.  GCC 7.4 or newer is required to resolve (PR83862)."
 fi
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking if $CC compiles with -mabi=ieeelongdouble and -mlong-double-128" >&5
+$as_echo_n "checking if $CC compiles with -mabi=ieeelongdouble and -mlong-double-128... " >&6; }
+if ${libc_cv_compiler_powerpc64le_ldbl128_mabi+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  save_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -mabi=ieeelongdouble -mlong-double-128"
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+long double x;
+
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+  libc_cv_compiler_powerpc64le_ldbl128_mabi=yes
+else
+  libc_cv_compiler_powerpc64le_ldbl128_mabi=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+CFLAGS="$save_CFLAGS"
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_compiler_powerpc64le_ldbl128_mabi" >&5
+$as_echo "$libc_cv_compiler_powerpc64le_ldbl128_mabi" >&6; }
+if test "$libc_cv_compiler_powerpc64le_ldbl128_mabi" == "no"; then :
+  critic_missing="$critic_missing The compiler must support -mabi=ieeelongdouble and -mlongdouble simultaneously."
+fi
+
 for ac_prog in $OBJCOPY
 do
   # Extract the first word of "$ac_prog", so it can be a program name with args.
diff --git a/sysdeps/powerpc/powerpc64/le/configure.ac b/sysdeps/powerpc/powerpc64/le/configure.ac
index 405933e710..769c06709e 100644
--- a/sysdeps/powerpc/powerpc64/le/configure.ac
+++ b/sysdeps/powerpc/powerpc64/le/configure.ac
@@ -51,6 +51,21 @@ CFLAGS="$save_CFLAGS"])
 AS_IF([test "$libc_cv_compiler_powerpc64le_ice" != "yes"],
       [critic_missing="$critic_missing __builtin_signbit is broken.  GCC 7.4 or newer is required to resolve (PR83862)."])
 
+dnl Some old compiler versions give out error messages when combining
+dnl -mabi=% and -mlong-double-128.  i.e GCC 7.5.0 (PR94200)
+AC_CACHE_CHECK([if $CC compiles with -mabi=ieeelongdouble and -mlong-double-128],
+	       libc_cv_compiler_powerpc64le_ldbl128_mabi, [dnl
+save_CFLAGS="$CFLAGS"
+CFLAGS="$CFLAGS -mabi=ieeelongdouble -mlong-double-128"
+AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+long double x;
+]])],
+		  [libc_cv_compiler_powerpc64le_ldbl128_mabi=yes],
+		  [libc_cv_compiler_powerpc64le_ldbl128_mabi=no])
+CFLAGS="$save_CFLAGS"])
+AS_IF([test "$libc_cv_compiler_powerpc64le_ldbl128_mabi" == "no"],
+      [critic_missing="$critic_missing The compiler must support -mabi=ieeelongdouble and -mlongdouble simultaneously."])
+
 dnl objcopy (binutils) 2.26 or newer required to support the --update-section
 dnl feature for fixing up .gnu.attribute section with IEEE ldbl.
 AC_CHECK_PROG_VER(OBJCOPY, $OBJCOPY, --version,