http://gcc.gnu.org/ml/gcc-patches/2008-10/msg00269.html

On glibc the libc.so carries a copy of the math function copysignl() but
contains unresolved symbols, any attempt to link against libgcc_s
without explicitely specifying -lm fails, resulting in a broken
bootstrap of the compiler.


diff -durN gcc-4.4.5.orig/gcc/config/t-slibgcc-elf-ver gcc-4.4.5/gcc/config/t-slibgcc-elf-ver
--- gcc-4.4.5.orig/gcc/config/t-slibgcc-elf-ver	2010-01-04 16:13:08.000000000 +0100
+++ gcc-4.4.5/gcc/config/t-slibgcc-elf-ver	2010-10-09 23:14:18.000000000 +0200
@@ -9,7 +9,7 @@
 SHLIB_OBJS = @shlib_objs@
 SHLIB_DIR = @multilib_dir@
 SHLIB_SLIBDIR_QUAL = @shlib_slibdir_qual@
-SHLIB_LC = -lc
+SHLIB_LC = @libgcc_libm@ -lc
 SHLIB_MAKE_SOLINK = $(LN_S) $(SHLIB_SONAME) $(SHLIB_DIR)/$(SHLIB_SOLINK)
 SHLIB_INSTALL_SOLINK = $(LN_S) $(SHLIB_SONAME) \
 	$$(DESTDIR)$$(slibdir)$(SHLIB_SLIBDIR_QUAL)/$(SHLIB_SOLINK)
diff -durN gcc-4.4.5.orig/libgcc/configure gcc-4.4.5/libgcc/configure
--- gcc-4.4.5.orig/libgcc/configure	2008-11-20 18:13:01.000000000 +0100
+++ gcc-4.4.5/libgcc/configure	2010-10-09 23:14:18.000000000 +0200
@@ -272,7 +272,7 @@
 PACKAGE_BUGREPORT=''
 
 ac_unique_file="static-object.mk"
-ac_subst_vars='SHELL PATH_SEPARATOR PACKAGE_NAME PACKAGE_TARNAME PACKAGE_VERSION PACKAGE_STRING PACKAGE_BUGREPORT exec_prefix prefix program_transform_name bindir sbindir libexecdir datadir sysconfdir sharedstatedir localstatedir libdir includedir oldincludedir infodir mandir build_alias host_alias target_alias DEFS ECHO_C ECHO_N ECHO_T LIBS libgcc_topdir enable_shared slibdir INSTALL_PROGRAM INSTALL_SCRIPT INSTALL_DATA AWK build build_cpu build_vendor build_os host host_cpu host_vendor host_os host_noncanonical build_libsubdir build_subdir host_subdir target_subdir AR ac_ct_AR LIPO ac_ct_LIPO NM ac_ct_NM RANLIB ac_ct_RANLIB STRIP ac_ct_STRIP LN_S CC CFLAGS LDFLAGS CPPFLAGS ac_ct_CC EXEEXT OBJEXT CPP decimal_float enable_decimal_float fixed_point vis_hide set_have_cc_tls tmake_file extra_parts asm_hidden_op LIBOBJS LTLIBOBJS'
+ac_subst_vars='SHELL PATH_SEPARATOR PACKAGE_NAME PACKAGE_TARNAME PACKAGE_VERSION PACKAGE_STRING PACKAGE_BUGREPORT exec_prefix prefix program_transform_name bindir sbindir libexecdir datadir sysconfdir sharedstatedir localstatedir libdir includedir oldincludedir infodir mandir build_alias host_alias target_alias DEFS ECHO_C ECHO_N ECHO_T LIBS libgcc_topdir enable_shared slibdir INSTALL_PROGRAM INSTALL_SCRIPT INSTALL_DATA AWK build build_cpu build_vendor build_os host host_cpu host_vendor host_os host_noncanonical build_libsubdir build_subdir host_subdir target_subdir AR ac_ct_AR LIPO ac_ct_LIPO NM ac_ct_NM RANLIB ac_ct_RANLIB STRIP ac_ct_STRIP LN_S CC CFLAGS LDFLAGS CPPFLAGS ac_ct_CC EXEEXT OBJEXT CPP decimal_float enable_decimal_float fixed_point vis_hide set_have_cc_tls LIBGCC_LIBM tmake_file extra_parts asm_hidden_op LIBOBJS LTLIBOBJS'
 ac_subst_files=''
 ac_pwd=`pwd`
 
@@ -3547,6 +3547,39 @@
 fi
 
 
+# On powerpc libgcc_s references copysignl which is a libm function but
+# glibc apparently also provides it via libc as opposed to uClibc where
+# it lives in libm.
+echo "$as_me:$LINENO: checking for library containing copysignl" >&5
+echo $ECHO_N "checking for library containing copysignl... $ECHO_C" >&6
+if test "${libgcc_cv_copysignl_lib+set}" = set; then
+  echo $ECHO_N "(cached) $ECHO_C" >&6
+else
+
+    echo '#include <features.h>' > conftest.c
+    echo 'int the_libc = __UCLIBC__ + __powerpc__;' >> conftest.c
+    libgcc_cv_copysignl_lib="-lc"
+    if { ac_try='${CC-cc} -S conftest.c -o conftest.s 1>&5'
+  { (eval echo "$as_me:$LINENO: \"$ac_try\"") >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  echo "$as_me:$LINENO: \$? = $ac_status" >&5
+  (exit $ac_status); }; }
+    then
+	libgcc_cv_copysignl_lib="-lm"
+    fi
+    rm -f conftest.*
+
+fi
+echo "$as_me:$LINENO: result: $libgcc_cv_copysignl_lib" >&5
+echo "${ECHO_T}$libgcc_cv_copysignl_lib" >&6
+
+case /${libgcc_cv_copysignl_lib}/ in
+  /-lm/) LIBGCC_LIBM="$LIBGCC_LIBM -lm" ;;
+  *) LIBGCC_LIBM= ;;
+esac
+
+
 # Conditionalize the makefile for this target machine.
 tmake_file_=
 for f in ${tmake_file}
@@ -4267,6 +4300,7 @@
 s,@fixed_point@,$fixed_point,;t t
 s,@vis_hide@,$vis_hide,;t t
 s,@set_have_cc_tls@,$set_have_cc_tls,;t t
+s,@LIBGCC_LIBM@,$LIBGCC_LIBM,;t t
 s,@tmake_file@,$tmake_file,;t t
 s,@extra_parts@,$extra_parts,;t t
 s,@asm_hidden_op@,$asm_hidden_op,;t t
diff -durN gcc-4.4.5.orig/libgcc/configure.ac gcc-4.4.5/libgcc/configure.ac
--- gcc-4.4.5.orig/libgcc/configure.ac	2008-11-20 18:13:01.000000000 +0100
+++ gcc-4.4.5/libgcc/configure.ac	2010-10-09 23:14:18.000000000 +0200
@@ -223,6 +223,27 @@
 fi
 AC_SUBST(set_have_cc_tls)
 
+# On powerpc libgcc_s references copysignl which is a libm function but
+# glibc apparently also provides it via libc as opposed to uClibc where
+# it lives in libm.
+AC_CACHE_CHECK
+  libgcc_cv_copysignl_lib,
+    echo '#include <features.h>' > conftest.c
+    echo 'int the_libc = __UCLIBC__ + __powerpc__;' >> conftest.c
+    libgcc_cv_copysignl_lib="-lc"
+    if AC_TRY_COMMAND(${CC-cc} -S conftest.c -o conftest.s 1>&AS_MESSAGE_LOG_FD)
+    then
+	libgcc_cv_copysignl_lib="-lm"
+    fi
+    rm -f conftest.*
+  ])
+
+case /${libgcc_cv_copysignl_lib}/ in
+  /-lm/) LIBGCC_LIBM="$LIBGCC_LIBM -lm" ;;
+  *) LIBGCC_LIBM= ;;
+esac
+AC_SUBST(LIBGCC_LIBM)
+
 # Conditionalize the makefile for this target machine.
 tmake_file_=
 for f in ${tmake_file}
diff -durN gcc-4.4.5.orig/libgcc/Makefile.in gcc-4.4.5/libgcc/Makefile.in
--- gcc-4.4.5.orig/libgcc/Makefile.in	2009-04-10 01:23:07.000000000 +0200
+++ gcc-4.4.5/libgcc/Makefile.in	2010-10-09 23:14:18.000000000 +0200
@@ -39,6 +39,7 @@
 decimal_float = @decimal_float@
 enable_decimal_float = @enable_decimal_float@
 fixed_point = @fixed_point@
+LIBGCC_LIBM = @LIBGCC_LIBM@
 
 host_noncanonical = @host_noncanonical@
 
@@ -787,9 +788,10 @@
 		@multilib_dir@,$(MULTIDIR),$(subst \
 		@shlib_objs@,$(objects),$(subst \
 		@shlib_base_name@,libgcc_s,$(subst \
+		@libgcc_libm@,$(LIBGCC_LIBM),$(subst \
 		@shlib_map_file@,$(mapfile),$(subst \
 		@shlib_slibdir_qual@,$(MULTIOSSUBDIR),$(subst \
-		@shlib_slibdir@,$(shlib_slibdir),$(SHLIB_LINK))))))))
+		@shlib_slibdir@,$(shlib_slibdir),$(SHLIB_LINK)))))))))
 
 libunwind$(SHLIB_EXT): $(libunwind-s-objects) $(extra-parts)
 	# @multilib_flags@ is still needed because this may use
