Avoid build multiarch if compiler warns about mismatched alias

GCC 8 emits an warning for alias for functions with incompatible types
and it is used extensivelly for ifunc resolvers implementations in C
(for instance on weak_alias with the internal symbol name to the
external one or with the libc_hidden_def to set ifunc for internal
usage).

This breaks the build when the ifunc resolver is not defined using
gcc attribute extensions (HAVE_GCC_IFUNC being 0).  Although for
all currently architectures that have multiarch support this compiler
options is enabled for default, there is still the option where the
user might try build glibc with a compiler without support for such
extension.  In this case this patch just disable the multiarch folder
in sysdeps selections.

GCC 7 and before still builds IFUNCs regardless of compiler support
(although for the lack of attribute support debug information would
be optimal).

Checked with a build on multiarch support architectures (aarch64,
arm, sparc, s390, powerpc, x86_64, i386) with multiarch enable
and disable and with GCC 7 and GCC 8.

	* configure.ac (libc_cv_gcc_incompatbile_alias): New define:
	indicates whether compiler emits an warning for alias for
	functions with incompatible types.

diff --git a/ChangeLog b/ChangeLog
index 66a500b78cce9acf0318f4a6c7597440101b9042..aa7e9a96c58e788704ab876e0086b0b052f9570b 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,9 @@
 2017-10-20  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
+       * configure.ac (libc_cv_gcc_incompatbile_alias): New define:
+       indicates whether compiler emits an warning for alias for
+       functions with incompatible types.
+
        [BZ #22273]
        * sysdeps/unix/sysv/linux/spawni.c (__spawnix): Handle the case where
        the auxiliary process is terminated by a signal before calling _exit

diff --git a/configure b/configure
index c2c9c72d5a913430ce3bffe0324f32370c69be11..6010977c58e31187f126152b85402a7db94bc8a2 100755 (executable)
--- a/configure
+++ b/configure
@@ -3996,6 +3996,32 @@ fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_indirect_function" >&5
 $as_echo "$libc_cv_gcc_indirect_function" >&6; }
 
+# Check if gcc warns about alias for function with incompatible types.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking if compiler warns about alias for function with incompatible types" >&5
+$as_echo_n "checking if compiler warns about alias for function with incompatible types... " >&6; }
+if ${libc_cv_gcc_incompatible_alias+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat > conftest.c <<EOF
+int __redirect_foo (const void *s, int c);
+
+__typeof (__redirect_foo) *foo_impl (void) __asm__ ("foo");
+__typeof (__redirect_foo) *foo_impl (void)
+{
+  return 0;
+}
+
+extern __typeof (__redirect_foo) foo_alias __attribute__ ((alias ("foo")));
+EOF
+libc_cv_gcc_incompatible_alias=yes
+if ${CC-cc} -Werror -c conftest.c -o conftest.o 1>&5 2>&5 ; then
+  libc_cv_gcc_incompatible_alias=no
+fi
+rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_gcc_incompatible_alias" >&5
+$as_echo "$libc_cv_gcc_incompatible_alias" >&6; }
+
 if test x"$libc_cv_ld_gnu_indirect_function" != xyes; then
   if test x"$multi_arch" = xyes; then
     as_fn_error $? "--enable-multi-arch support requires assembler and linker support" "$LINENO" 5
@@ -4003,12 +4029,25 @@ if test x"$libc_cv_ld_gnu_indirect_function" != xyes; then
     multi_arch=no
   fi
 fi
-if test x"$libc_cv_gcc_indirect_function" != xyes &&
-   test x"$multi_arch" = xyes; then
-  { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: --enable-multi-arch support recommends a gcc with gnu-indirect-function support.
+if test x"$libc_cv_gcc_indirect_function" != xyes; then
+  # GCC 8+ emits a warning for alias with incompatible types and it might
+  # fail to build ifunc resolvers aliases to either weak or internal
+  # symbols.  Disables multiarch build in this case.
+  if test x"$libc_cv_gcc_incompatible_alias" == xyes; then
+    { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: gcc emits a warning for alias between functions of incompatible types" >&5
+$as_echo "$as_me: WARNING: gcc emits a warning for alias between functions of incompatible types" >&2;}
+    if test x"$multi_arch" = xyes; then
+      as_fn_error $? "--enable-multi-arch support requires a gcc with gnu-indirect-function support" "$LINENO" 5
+    fi
+    { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: Multi-arch is disabled." >&5
+$as_echo "$as_me: WARNING: Multi-arch is disabled." >&2;}
+    multi_arch=no
+  elif test x"$multi_arch" = xyes; then
+    { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: --enable-multi-arch support recommends a gcc with gnu-indirect-function support.
 Please use a gcc which supports it by default or configure gcc with --enable-gnu-indirect-function" >&5
 $as_echo "$as_me: WARNING: --enable-multi-arch support recommends a gcc with gnu-indirect-function support.
 Please use a gcc which supports it by default or configure gcc with --enable-gnu-indirect-function" >&2;}
+  fi
 fi
 multi_arch_d=
 if test x"$multi_arch" != xno; then

diff --git a/configure.ac b/configure.ac
index 195e81acfd05a719a4597b6cefb1b3af177f9ac4..148f7d1682c4f76b3e51ec435a2ff1a1a168f8c1 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -634,6 +634,26 @@ if ${CC-cc} -c conftest.c -o conftest.o 1>&AS_MESSAGE_LOG_FD \
 fi
 rm -f conftest*])
 
+# Check if gcc warns about alias for function with incompatible types.
+AC_CACHE_CHECK([if compiler warns about alias for function with incompatible types],
+              libc_cv_gcc_incompatible_alias, [dnl
+cat > conftest.c <<EOF
+int __redirect_foo (const void *s, int c);
+
+__typeof (__redirect_foo) *foo_impl (void) __asm__ ("foo");
+__typeof (__redirect_foo) *foo_impl (void)
+{
+  return 0;
+}
+
+extern __typeof (__redirect_foo) foo_alias __attribute__ ((alias ("foo")));
+EOF
+libc_cv_gcc_incompatible_alias=yes
+if ${CC-cc} -Werror -c conftest.c -o conftest.o 1>&AS_MESSAGE_LOG_FD 2>&AS_MESSAGE_LOG_FD ; then
+  libc_cv_gcc_incompatible_alias=no
+fi
+rm -f conftest*])
+
 if test x"$libc_cv_ld_gnu_indirect_function" != xyes; then
   if test x"$multi_arch" = xyes; then
     AC_MSG_ERROR([--enable-multi-arch support requires assembler and linker support])
@@ -641,10 +661,21 @@ if test x"$libc_cv_ld_gnu_indirect_function" != xyes; then
     multi_arch=no
   fi
 fi
-if test x"$libc_cv_gcc_indirect_function" != xyes &&
-   test x"$multi_arch" = xyes; then
-  AC_MSG_WARN([--enable-multi-arch support recommends a gcc with gnu-indirect-function support.
+if test x"$libc_cv_gcc_indirect_function" != xyes; then
+  # GCC 8+ emits a warning for alias with incompatible types and it might
+  # fail to build ifunc resolvers aliases to either weak or internal
+  # symbols.  Disables multiarch build in this case.
+  if test x"$libc_cv_gcc_incompatible_alias" == xyes; then
+    AC_MSG_WARN([gcc emits a warning for alias between functions of incompatible types])
+    if test x"$multi_arch" = xyes; then
+      AC_MSG_ERROR([--enable-multi-arch support requires a gcc with gnu-indirect-function support])
+    fi
+    AC_MSG_WARN([Multi-arch is disabled.])
+    multi_arch=no
+  elif test x"$multi_arch" = xyes; then
+    AC_MSG_WARN([--enable-multi-arch support recommends a gcc with gnu-indirect-function support.
 Please use a gcc which supports it by default or configure gcc with --enable-gnu-indirect-function])
+  fi
 fi
 multi_arch_d=
 if test x"$multi_arch" != xno; then