Darwin: Rework handling for unwinder code in libgcc_s and specs [PR80556].

This addresses a long-standing problem where a work-around for an unwinder
issue (also a regression) regresses other functionality.  The patch replaces
several work-arounds with a fix for PR80556 and a work-around for PR88590.

* The fix for PR80556 requires a bump to the SO name for libgcc_s, since we
need to remove the unwinder symbols from it.  This would trigger PR88590
hence the work-around for that.

* We weaken the symbols for emulated TLS support so that it is possible
for a DSO linked with static-libgcc to interoperate with a DSO linked with
libgcc_s.  Likewise main exes.

* We remove all the gcc-4.2.1 era stubs machinery and workarounds.

* libgcc is always now linked ahead of libc, which avoids fails where the
libc (libSystem) builtins implementations are not up to date.

* The unwinder now always comes from the system
 - for Darwin9 from /usr/lib/libgcc_s.1.dylib
 - for Darwin10 from /usr/lib/libSystem.dylib
 - for Darwin11+ from /usr/lib/system/libunwind.dylib.

 We still insert a shim on Darwin10 to fix an omitted unwind function, but
 the underlying unwinder remains the system one.

* The work-around for PR88590 has two parts (1) we always link libgcc from
its convenience lib on affected system versions (avoiding the need to find
the DSO path); (2) we add and export the emutls functions from DSOs - this
makes a relatively small (20k) addition to a DSO.  These can be backed out
when a proper fix for PR88590 is committed.

For distributions that wish to install a libgcc_s.1.dylib to satisfy linkage
from exes that linked against the stubs can use a reexported libgcc_s.1.1
(since that contains all the symbols that were previously exported via the
 stubs).

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

gcc/ChangeLog:

	PR target/80556
	* config/darwin-driver.c (darwin_driver_init): Handle exported
	symbols and symbol lists (suppress automatic export of the TLS
	symbols).
	* config/darwin.c (darwin_rename_builtins): Remove workaround.
	* config/darwin.h (LINK_GCC_C_SEQUENCE_SPEC): Likewise.
	(REAL_LIBGCC_SPEC): Handle revised library uses.
	* config/darwin.opt (nodefaultexport): New.
	* config/i386/darwin.h (PR80556_WORKAROUND): Remove.
	* config/i386/darwin32-biarch.h (PR80556_WORKAROUND): Likewise.
	* config/i386/darwin64-biarch.h (PR80556_WORKAROUND): Likewise.

libgcc/ChangeLog:

	* config.host: Add weak emutls crt to the extra_parts.
	* config/i386/darwin-lib.h (DECLARE_LIBRARY_RENAMES): Remove
	workaround.
	* config/libgcc-libsystem.ver: Add exclude list for the system-
	provided unwinder.
	* config/t-slibgcc-darwin: Bump SO version, remove stubs code.
	* config/i386/libgcc-darwin.10.4.ver: Removed.
	* config/i386/libgcc-darwin.10.5.ver: Removed.
	* config/rs6000/libgcc-darwin.10.4.ver: Removed.
	* config/rs6000/libgcc-darwin.10.5.ver: Removed.
	* config/t-darwin-noeh: New file.

gcc/testsuite/ChangeLog:

	* gcc.dg/torture/fp-int-convert-timode-3.c: Remove XFAIL.
	* gcc.dg/torture/fp-int-convert-timode-4.c: Likewise.

8 files changed, 61 insertions, 463 deletions

diff --git a/libgcc/config/i386/darwin-lib.h b/libgcc/config/i386/darwin-lib.h
index 5aeee33..e22f732 100644
--- a/libgcc/config/i386/darwin-lib.h
+++ b/libgcc/config/i386/darwin-lib.h
@@ -22,13 +22,4 @@ a copy of the GCC Runtime Library Exception along with this program;
 see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 <http://www.gnu.org/licenses/>.  */
 
-/* The system ___divdc3 routine in libSystem on darwin10 is not
-   accurate to 1ulp, ours is, so we avoid ever using the system name
-   for this routine and instead install a non-conflicting name that is
-   accurate.  See darwin_rename_builtins.  */
-#ifdef L_divdc3
-#define DECLARE_LIBRARY_RENAMES \
-  asm(".text; ___divdc3: jmp ___ieee_divdc3 ; .globl ___divdc3");
-#endif
-
 extern void * _darwin10_Unwind_FindEnclosingFunction (void *);
diff --git a/libgcc/config/i386/libgcc-darwin.10.4.ver b/libgcc/config/i386/libgcc-darwin.10.4.ver
deleted file mode 100644
index b8a73b1..0000000
--- a/libgcc/config/i386/libgcc-darwin.10.4.ver
+++ /dev/null
@@ -1,98 +0,0 @@
-# Copyright (C) 2005-2021 Free Software Foundation, Inc.
-#
-# This file is part of GCC.
-#
-# GCC is free software; you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation; either version 3, or (at your option)
-# any later version.
-#
-# GCC is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with GCC; see the file COPYING3.  If not see
-# <http://www.gnu.org/licenses/>.
-__Unwind_Backtrace
-__Unwind_DeleteException
-__Unwind_FindEnclosingFunction
-__Unwind_Find_FDE
-__Unwind_ForcedUnwind
-__Unwind_GetCFA
-__Unwind_GetDataRelBase
-__Unwind_GetGR
-__Unwind_GetIP
-__Unwind_GetLanguageSpecificData
-__Unwind_GetRegionStart
-__Unwind_GetTextRelBase
-__Unwind_RaiseException
-__Unwind_Resume
-__Unwind_Resume_or_Rethrow
-__Unwind_SetGR
-__Unwind_SetIP
-___absvdi2
-___absvsi2
-___addvdi3
-___addvsi3
-___ashldi3
-___ashrdi3
-___clear_cache
-___clzdi2
-___clzsi2
-___cmpdi2
-___ctzdi2
-___ctzsi2
-___deregister_frame
-___deregister_frame_info
-___deregister_frame_info_bases
-___divdc3
-___divdi3
-___divsc3
-___divxc3
-___enable_execute_stack
-___ffsdi2
-___fixdfdi
-___fixsfdi
-___fixunsdfdi
-___fixunsdfsi
-___fixunssfdi
-___fixunssfsi
-___fixunsxfdi
-___fixunsxfsi
-___fixxfdi
-___floatdidf
-___floatdisf
-___floatdixf
-___gcc_personality_v0
-___lshrdi3
-___moddi3
-___muldc3
-___muldi3
-___mulsc3
-___mulvdi3
-___mulvsi3
-___mulxc3
-___negdi2
-___negvdi2
-___negvsi2
-___paritydi2
-___paritysi2
-___popcountdi2
-___popcountsi2
-___powidf2
-___powisf2
-___powixf2
-___register_frame
-___register_frame_info
-___register_frame_info_bases
-___register_frame_info_table
-___register_frame_info_table_bases
-___register_frame_table
-___subvdi3
-___subvsi3
-___ucmpdi2
-___udivdi3
-___udivmoddi4
-___umoddi3
diff --git a/libgcc/config/i386/libgcc-darwin.10.5.ver b/libgcc/config/i386/libgcc-darwin.10.5.ver
deleted file mode 100644
index 49fd927..0000000
--- a/libgcc/config/i386/libgcc-darwin.10.5.ver
+++ /dev/null
@@ -1,102 +0,0 @@
-# Copyright (C) 2005-2021 Free Software Foundation, Inc.
-#
-# This file is part of GCC.
-#
-# GCC is free software; you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation; either version 3, or (at your option)
-# any later version.
-#
-# GCC is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with GCC; see the file COPYING3.  If not see
-# <http://www.gnu.org/licenses/>.
-__Unwind_Backtrace
-__Unwind_DeleteException
-__Unwind_FindEnclosingFunction
-__Unwind_Find_FDE
-__Unwind_ForcedUnwind
-__Unwind_GetCFA
-__Unwind_GetDataRelBase
-__Unwind_GetGR
-__Unwind_GetIP
-__Unwind_GetIPInfo
-__Unwind_GetLanguageSpecificData
-__Unwind_GetRegionStart
-__Unwind_GetTextRelBase
-__Unwind_RaiseException
-__Unwind_Resume
-__Unwind_Resume_or_Rethrow
-__Unwind_SetGR
-__Unwind_SetIP
-___absvdi2
-___absvsi2
-___addvdi3
-___addvsi3
-___ashldi3
-___ashrdi3
-___clear_cache
-___clzdi2
-___clzsi2
-___cmpdi2
-___ctzdi2
-___ctzsi2
-___deregister_frame
-___deregister_frame_info
-___deregister_frame_info_bases
-___divdc3
-___divdi3
-___divsc3
-___divxc3
-___enable_execute_stack
-___ffsdi2
-___fixdfdi
-___fixsfdi
-___fixunsdfdi
-___fixunsdfsi
-___fixunssfdi
-___fixunssfsi
-___fixunsxfdi
-___fixunsxfsi
-___fixxfdi
-___floatdidf
-___floatdisf
-___floatdixf
-___floatundidf
-___floatundisf
-___floatundixf
-___gcc_personality_v0
-___lshrdi3
-___moddi3
-___muldc3
-___muldi3
-___mulsc3
-___mulvdi3
-___mulvsi3
-___mulxc3
-___negdi2
-___negvdi2
-___negvsi2
-___paritydi2
-___paritysi2
-___popcountdi2
-___popcountsi2
-___powidf2
-___powisf2
-___powixf2
-___register_frame
-___register_frame_info
-___register_frame_info_bases
-___register_frame_info_table
-___register_frame_info_table_bases
-___register_frame_table
-___subvdi3
-___subvsi3
-___ucmpdi2
-___udivdi3
-___udivmoddi4
-___umoddi3
diff --git a/libgcc/config/libgcc-libsystem.ver b/libgcc/config/libgcc-libsystem.ver
index 4763174..697a245 100644
--- a/libgcc/config/libgcc-libsystem.ver
+++ b/libgcc/config/libgcc-libsystem.ver
@@ -1 +1,37 @@
-_darwin10_Unwind_FindEnclosingFunction
+# We must use the unwinder provided by the OS, even if that has
+# limitations or bug, so exclude the libgcc_s symbols.
+
+%exclude {
+ _Unwind_DeleteException
+ _Unwind_Find_FDE
+ _Unwind_ForcedUnwind
+ _Unwind_GetGR
+ _Unwind_GetIP
+ _Unwind_GetLanguageSpecificData
+ _Unwind_GetRegionStart
+ _Unwind_GetTextRelBase
+ _Unwind_GetDataRelBase
+ _Unwind_RaiseException
+ _Unwind_Resume
+ _Unwind_SetGR
+ _Unwind_SetIP
+ _Unwind_SjLj_Register
+ _Unwind_SjLj_Unregister
+ _Unwind_SjLj_RaiseException
+ _Unwind_SjLj_ForcedUnwind
+ _Unwind_SjLj_Resume
+ _Unwind_FindEnclosingFunction
+ _Unwind_GetCFA
+ _Unwind_Backtrace
+ _Unwind_Resume_or_Rethrow
+ _Unwind_SjLj_Resume_or_Rethrow
+ _Unwind_GetIPInfo
+
+  __register_frame
+  __register_frame_table
+  __deregister_frame
+  __register_frame_info
+  __deregister_frame_info
+  __frame_state_for
+  __register_frame_info_table
+}
diff --git a/libgcc/config/rs6000/libgcc-darwin.10.4.ver b/libgcc/config/rs6000/libgcc-darwin.10.4.ver
deleted file mode 100644
index b050cb8..0000000
--- a/libgcc/config/rs6000/libgcc-darwin.10.4.ver
+++ /dev/null
@@ -1,93 +0,0 @@
-# Copyright (C) 2005-2021 Free Software Foundation, Inc.
-#
-# This file is part of GCC.
-#
-# GCC is free software; you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation; either version 3, or (at your option)
-# any later version.
-#
-# GCC is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with GCC; see the file COPYING3.  If not see
-# <http://www.gnu.org/licenses/>.
-__Unwind_Backtrace
-__Unwind_DeleteException
-__Unwind_FindEnclosingFunction
-__Unwind_Find_FDE
-__Unwind_ForcedUnwind
-__Unwind_GetCFA
-__Unwind_GetDataRelBase
-__Unwind_GetGR
-__Unwind_GetIP
-__Unwind_GetLanguageSpecificData
-__Unwind_GetRegionStart
-__Unwind_GetTextRelBase
-__Unwind_RaiseException
-__Unwind_Resume
-__Unwind_Resume_or_Rethrow
-__Unwind_SetGR
-__Unwind_SetIP
-___absvdi2
-___absvsi2
-___addvdi3
-___addvsi3
-___ashldi3
-___ashrdi3
-___clear_cache
-___clzdi2
-___clzsi2
-___cmpdi2
-___ctzdi2
-___ctzsi2
-___deregister_frame
-___deregister_frame_info
-___deregister_frame_info_bases
-___divdi3
-___enable_execute_stack
-___ffsdi2
-___fixdfdi
-___fixsfdi
-___fixtfdi
-___fixunsdfdi
-___fixunsdfsi
-___fixunssfdi
-___fixunssfsi
-___fixunstfdi
-___floatdidf
-___floatdisf
-___floatditf
-___gcc_personality_v0
-___gcc_qadd
-___gcc_qdiv
-___gcc_qmul
-___gcc_qsub
-___lshrdi3
-___moddi3
-___muldi3
-___mulvdi3
-___mulvsi3
-___negdi2
-___negvdi2
-___negvsi2
-___paritydi2
-___paritysi2
-___popcountdi2
-___popcountsi2
-___register_frame
-___register_frame_info
-___register_frame_info_bases
-___register_frame_info_table
-___register_frame_info_table_bases
-___register_frame_table
-___subvdi3
-___subvsi3
-___trampoline_setup
-___ucmpdi2
-___udivdi3
-___udivmoddi4
-___umoddi3
diff --git a/libgcc/config/rs6000/libgcc-darwin.10.5.ver b/libgcc/config/rs6000/libgcc-darwin.10.5.ver
deleted file mode 100644
index dcc548f..0000000
--- a/libgcc/config/rs6000/libgcc-darwin.10.5.ver
+++ /dev/null
@@ -1,106 +0,0 @@
-# Copyright (C) 2005-2021 Free Software Foundation, Inc.
-#
-# This file is part of GCC.
-#
-# GCC is free software; you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation; either version 3, or (at your option)
-# any later version.
-#
-# GCC is distributed in the hope that it will be useful,
-# but WITHOUT ANY WARRANTY; without even the implied warranty of
-# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-# GNU General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with GCC; see the file COPYING3.  If not see
-# <http://www.gnu.org/licenses/>.
-__Unwind_Backtrace
-__Unwind_DeleteException
-__Unwind_FindEnclosingFunction
-__Unwind_Find_FDE
-__Unwind_ForcedUnwind
-__Unwind_GetCFA
-__Unwind_GetDataRelBase
-__Unwind_GetGR
-__Unwind_GetIP
-__Unwind_GetIPInfo
-__Unwind_GetLanguageSpecificData
-__Unwind_GetRegionStart
-__Unwind_GetTextRelBase
-__Unwind_RaiseException
-__Unwind_Resume
-__Unwind_Resume_or_Rethrow
-__Unwind_SetGR
-__Unwind_SetIP
-___absvdi2
-___absvsi2
-___addvdi3
-___addvsi3
-___ashldi3
-___ashrdi3
-___clear_cache
-___clzdi2
-___clzsi2
-___cmpdi2
-___ctzdi2
-___ctzsi2
-___deregister_frame
-___deregister_frame_info
-___deregister_frame_info_bases
-___divdc3
-___divdi3
-___divsc3
-___divtc3
-___enable_execute_stack
-___ffsdi2
-___fixdfdi
-___fixsfdi
-___fixtfdi
-___fixunsdfdi
-___fixunsdfsi
-___fixunssfdi
-___fixunssfsi
-___fixunstfdi
-___floatdidf
-___floatdisf
-___floatditf
-___floatundidf
-___floatundisf
-___floatunditf
-___gcc_personality_v0
-___gcc_qadd
-___gcc_qdiv
-___gcc_qmul
-___gcc_qsub
-___lshrdi3
-___moddi3
-___muldc3
-___muldi3
-___mulsc3
-___multc3
-___mulvdi3
-___mulvsi3
-___negdi2
-___negvdi2
-___negvsi2
-___paritydi2
-___paritysi2
-___popcountdi2
-___popcountsi2
-___powidf2
-___powisf2
-___powitf2
-___register_frame
-___register_frame_info
-___register_frame_info_bases
-___register_frame_info_table
-___register_frame_info_table_bases
-___register_frame_table
-___subvdi3
-___subvsi3
-___trampoline_setup
-___ucmpdi2
-___udivdi3
-___udivmoddi4
-___umoddi3
diff --git a/libgcc/config/t-darwin-noeh b/libgcc/config/t-darwin-noeh
new file mode 100644
index 0000000..08d9c1a
--- /dev/null
+++ b/libgcc/config/t-darwin-noeh
@@ -0,0 +1,4 @@
+# Most Darwin versions get their unwinder from libSystem.
+# so remove the unwinder from the shared lib.
+# We still need it in the _eh.a for Darwin8/9.
+LIB2ADDEHSHARED =
diff --git a/libgcc/config/t-slibgcc-darwin b/libgcc/config/t-slibgcc-darwin
index bd1e963..1512267 100644
--- a/libgcc/config/t-slibgcc-darwin
+++ b/libgcc/config/t-slibgcc-darwin
@@ -1,43 +1,34 @@
 # Build a shared libgcc library with the darwin linker.
-SHLIB_SOVERSION = 1
-SHLIB_VERSTRING = -compatibility_version $(SHLIB_SOVERSION) -current_version $(SHLIB_SOVERSION).0
+
+SHLIB_SOVERSION = 1.1
+SHLIB_SO_MINVERSION = 1
+SHLIB_VERSTRING = -compatibility_version $(SHLIB_SO_MINVERSION) -current_version $(SHLIB_SOVERSION)
 SHLIB_EXT = .dylib
+SHLIB_LC = -lSystem
+
+# Shorthand expressions for the LINK below.
 SHLIB_INSTALL_NAME = @shlib_base_name@.$(SHLIB_SOVERSION)$(SHLIB_EXT)
-SHLIB_SONAME = @shlib_base_name@$(SHLIB_EXT)
-SHLIB_SOLINK = @shlib_base_name@.so
 SHLIB_MAP = @shlib_map_file@
-SHLIB_OBJS = @shlib_objs@
 SHLIB_DIR = @multilib_dir@
-SHLIB_LC = -lc
+SHLIB_SONAME = @shlib_base_name@$(SHLIB_EXT)
 
-# Darwin only searches in /usr/lib for shared libraries, not in subdirectories,
-# so the libgcc variants have different names not different locations.
-# Note that this version is used for the loader, not the linker; the linker
-# uses the stub versions named by the versioned members of $(INSTALL_FILES).
+# Darwin only searches in shlib_slibdir for shared libraries, not in
+# subdirectories.  The link builds one architecture slice in its designated
+# subdir.  The code under MULTIBUILDTOP combines these into a single FAT
+# library, that is what we eventually install.
 
 SHLIB_LINK = $(CC) $(LIBGCC2_CFLAGS) $(LDFLAGS) -dynamiclib -nodefaultlibs \
 	-install_name @shlib_slibdir@/$(SHLIB_INSTALL_NAME) \
 	-single_module -o $(SHLIB_DIR)/$(SHLIB_SONAME) \
 	-Wl,-exported_symbols_list,$(SHLIB_MAP) \
 	$(SHLIB_VERSTRING) \
-	@multilib_flags@ $(SHLIB_OBJS) $(SHLIB_LC)
+	@multilib_flags@ @shlib_objs@ $(SHLIB_LC)
 
 SHLIB_MKMAP = $(srcdir)/mkmap-flat.awk
 SHLIB_MKMAP_OPTS = -v leading_underscore=1
-SHLIB_VERPFX = $(srcdir)/config/$(cpu_type)/libgcc-darwin
-
-# we're only going to build the stubs if the target slib is /usr/lib
-# there is no other case in which they're useful in a live system.
-ifeq (/usr/lib,$(shlib_slibdir))
-LGCC_STUBS = libgcc_s.10.4.dylib libgcc_s.10.5.dylib
-else
-LGCC_STUBS =
-endif
 
 LGCC_FILES = libgcc_s.$(SHLIB_SOVERSION)$(SHLIB_EXT)
-LGCC_FILES += $(LGCC_STUBS)
-LEXT_STUBS = libgcc_ext.10.4$(SHLIB_EXT) libgcc_ext.10.5$(SHLIB_EXT)
-LGCC_FILES += $(LEXT_STUBS)
+
 INSTALL_FILES=$(LGCC_FILES)
 
 # we do our own thing
@@ -51,33 +42,6 @@ all: $(INSTALL_FILES)
 install-leaf: install-darwin-libgcc-stubs
 endif
 
-# In order to support -mmacosx-version-min, you need to have multiple
-# different libgcc_s libraries that actually get linked against, one for
-# each system version supported.  They are 'stub' libraries that
-# contain no code, just a list of exported symbols.
-# The actual use of the libraries is controlled by REAL_LIBGCC_SPEC.
-#
-# This assumes each multilib corresponds to a different architecture.
-libgcc_s.%.dylib : all-multi $(SHLIB_VERPFX).%.ver libgcc_s$(SHLIB_EXT)
-	MLIBS=`$(CC) --print-multi-lib | sed -e 's/;.*$$//'` ; \
-	for mlib in $$MLIBS ; do \
-	  $(STRIP) -o $(@)_T$${mlib} \
-	    -s $(SHLIB_VERPFX).$(*).ver -c -u \
-	    ../$${mlib}/libgcc/$${mlib}/libgcc_s$(SHLIB_EXT)  || exit 1 ; \
-	done
-	$(LIPO) -output $@ -create $(@)_T*
-	rm $(@)_T*
-
-libgcc_ext.%.dylib : all-multi $(SHLIB_VERPFX).%.ver libgcc_s$(SHLIB_EXT) 
-	MLIBS=`$(CC) --print-multi-lib | sed -e 's/;.*$$//'` ; \
-	for mlib in $$MLIBS ; do \
-	  $(STRIP) -o $(@)_T$${mlib} \
-	    -R $(SHLIB_VERPFX).$(*).ver -c -urx \
-	    ../$${mlib}/libgcc/$${mlib}/libgcc_s$(SHLIB_EXT) || exit 1 ; \
-	done
-	$(LIPO) -output $@ -create $(@)_T*
-	rm $(@)_T*
-
 libgcc_s.$(SHLIB_SOVERSION)$(SHLIB_EXT): all-multi libgcc_s$(SHLIB_EXT)
 	MLIBS=`$(CC) --print-multi-lib | sed -e 's/;.*$$//'` ; \
 	for mlib in $$MLIBS ; do \
@@ -88,6 +52,8 @@ libgcc_s.$(SHLIB_SOVERSION)$(SHLIB_EXT): all-multi libgcc_s$(SHLIB_EXT)
 	  -create libgcc_s.$(SHLIB_SOVERSION)$(SHLIB_EXT)_T*
 	rm libgcc_s.$(SHLIB_SOVERSION)$(SHLIB_EXT)_T*
 
+# Install the shared library.
+
 install-darwin-libgcc-stubs :
 	$(mkinstalldirs) $(DESTDIR)$(slibdir)
 	for d in $(INSTALL_FILES) ; do \
@@ -96,10 +62,10 @@ install-darwin-libgcc-stubs :
 
 else
 
-# Do not install shared libraries for any other multilibs.  Unless
-# we're putting them in the gcc directory during a build, for
-# compatibility with the pre-top-level layout.  In that case we
-# need symlinks.
+# Do not install shared libraries for any other multilibs.  Unless we are
+# putting them in the gcc directory during a build, for compatibility with
+# the pre-top-level layout.  In that case we provide symlinks to the FAT lib
+# from the sub-directories.
 
 ifeq ($(enable_shared),yes)
 all: install-darwin-libgcc-links