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Re: Avoid use of libgcc_s and libgcc_eh when building glibc


On Tue, 29 May 2012, Roland McGrath wrote:

> I haven't given it deep thought, but I don't see any problems.
> We certainly need some comments in the makefiles explaining what
> the linking differences are between the tests and non-tests and
> why those matter.

Here is a version with an extended comment added.

I'd like architecture maintainers to test this, for all libc architectures 
and for IA64.  (Hurd testing would be good as well if possible.)  It seems 
quite likely that IA64 may need

gnulib-arch = $(libgcc_eh)
static-gnulib-arch = -lgcc_eh $(libunwind)

in its sysdeps makefiles (that setting means you don't get the 
bootstrapping benefits of this patch, but as previously noted IA64 doesn't 
support such bootstrapping on the GCC side either).

2012-05-30  Joseph Myers  <joseph@codesourcery.com>

	* Makeconfig [!+link] (+link-before-libc): New variable.
	[!+link] (+link-after-libc): Likewise.
	[!+link] (+link-tests): Likewise.
	[!+link] (+link): Define in terms of $(+link-before-libc) and
	$(+link-after-libc).
	[!+link-static] (+link-static-before-libc): New variable.
	[!+link-static] (+link-static-after-libc): Likewise.
	[!+link-static] (+link-static-tests): Likewise.
	[!+link-static] (+link-static): Define in terms of
	$(+link-static-before-libc) and $(+link-static-after-libc).
	[build-shared] (link-libc-before-gnulib): New variable.
	[build-shared] (link-libc-tests): Likewise.
	[build-shared] (link-libc): Define in terms of
	$(link-libc-before-gnulib).
	[!build-shared] (link-libc-tests): New variable.
	(link-libc-static-tests): New variable.
	[!gnulib] (gnulib-arch): New variable.
	[!gnulib] (gnulib-tests): Likewise.
	[!gnulib] (static-gnulib-arch): Likewise.
	[!gnulib] (static-gnulib-tests): Likewise.
	[!gnulib] (gnulib): Use $(gnulib-arch).  Do not use $(libgcc_eh).
	Define with "=" instead of ":=".
	[!gnulib] (static-gnulib): Use $(static-gnulib-arch).  Do not use
	-lgcc_eh $(libunwind).  Define with "=" instead of ":=".
	* Rules (binaries-all-notests): New variable.
	(binaries-all-tests): Likewise.
	(binaries-static-notests): Likewise.
	(binaries-static-tests): Likewise.
	(binaries-all): Define using $(binaries-all-notests) and
	$(binaries-all-tests).
	(binaries-static): Define using $(binaries-static-notests) and
	$(binaries-static-tests).
	(binaries-shared-tests): New variable.
	(binaries-shared-notests): Likewise.
	(binaries-shared): Remove variable.
	($(addprefix $(objpfx),$(binaries-shared-notests))): New rule.
	($(addprefix $(objpfx),$(binaries-shared-tests))): Likewise.
	($(addprefix $(objpfx),$(binaries-shared))): Remove rule.
	($(addprefix $(objpfx),$(binaries-static-notests))): New rule.
	($(addprefix $(objpfx),$(binaries-static-tests))): Likewise.
	($(addprefix $(objpfx),$(binaries-static))): Remove rule.
	* elf/Makefile (sln-modules): New variable.
	(extra-objs): Add $(sln-modules:=.o).
	(ldconfig-modules): Add static-stubs.
	($(objpfx)sln): Depend on $(sln-modules:%=$(objpfx)%.o).
	* elf/static-stubs.c: New file.

diff --git a/Makeconfig b/Makeconfig
index b4b2963..3be39ae 100644
--- a/Makeconfig
+++ b/Makeconfig
@@ -415,9 +415,9 @@ LDFLAGS.so += $(hashstyle-LDFLAGS)
 LDFLAGS-rtld += $(hashstyle-LDFLAGS)
 endif
 
-# Command for linking programs with the C library.
+# Commands for linking programs with the C library.
 ifndef +link
-+link = $(CC) -nostdlib -nostartfiles -o $@ \
++link-before-libc = $(CC) -nostdlib -nostartfiles -o $@ \
 	      $(sysdep-LDFLAGS) $(config-LDFLAGS) $(LDFLAGS) $(LDFLAGS-$(@F)) \
 	      $(combreloc-LDFLAGS) $(relro-LDFLAGS) $(hashstyle-LDFLAGS) \
 	      $(addprefix $(csu-objpfx),$(start-installed-name)) \
@@ -426,7 +426,10 @@ ifndef +link
 						     $(start-installed-name))\
 			   $(+preinit) $(link-extra-libs) \
 			   $(common-objpfx)libc% $(+postinit),$^) \
-	      $(link-extra-libs) $(link-libc) $(+postctor) $(+postinit)
+	      $(link-extra-libs)
++link-after-libc = $(+postctor) $(+postinit)
++link = $(+link-before-libc) $(link-libc) $(+link-after-libc)
++link-tests = $(+link-before-libc) $(link-libc-tests) $(+link-after-libc)
 endif
 # Command for linking PIE programs with the C library.
 ifndef +link-pie
@@ -443,7 +446,7 @@ ifndef +link-pie
 endif
 # Command for statically linking programs with the C library.
 ifndef +link-static
-+link-static = $(CC) -nostdlib -nostartfiles -static -o $@ \
++link-static-before-libc = $(CC) -nostdlib -nostartfiles -static -o $@ \
 	      $(sysdep-LDFLAGS) $(LDFLAGS) $(LDFLAGS-$(@F))  \
 	      $(addprefix $(csu-objpfx),$(static-start-installed-name)) \
 	      $(+preinit) $(+prector) \
@@ -451,7 +454,12 @@ ifndef +link-static
 						     $(start-installed-name))\
 			   $(+preinit) $(link-extra-libs-static) \
 			   $(common-objpfx)libc% $(+postinit),$^) \
-	      $(link-extra-libs-static) $(link-libc-static) $(+postctor) $(+postinit)
+	      $(link-extra-libs-static) $(link-libc-static)
++link-static-after-libc = $(+postctor) $(+postinit)
++link-static = $(+link-static-before-libc) $(link-libc-static) \
+	       $(+link-static-after-libc)
++link-static-tests = $(+link-static-before-libc) $(link-libc-static-tests) \
+		     $(+link-static-after-libc)
 endif
 # Command for statically linking bounded-pointer programs with the C library.
 ifndef +link-bounded
@@ -475,10 +483,12 @@ ifeq (yes,$(build-shared))
 # We need the versioned name of libc.so in the deps of $(others) et al
 # so that the symlink to libc.so is created before anything tries to
 # run the linked programs.
-link-libc = -Wl,-rpath-link=$(rpath-link) \
+link-libc-before-gnulib = -Wl,-rpath-link=$(rpath-link) \
 	    $(common-objpfx)libc.so$(libc.so-version) \
 	    $(common-objpfx)$(patsubst %,$(libtype.oS),c) \
-	    $(as-needed) $(common-objpfx)elf/ld.so $(no-as-needed) $(gnulib)
+	    $(as-needed) $(common-objpfx)elf/ld.so $(no-as-needed)
+link-libc = $(link-libc-before-gnulib) $(gnulib)
+link-libc-tests = $(link-libc-before-gnulib) $(gnulib-tests)
 # This is how to find at build-time things that will be installed there.
 rpath-dirs = math elf dlfcn nss nis rt resolv crypt
 rpath-link = \
@@ -488,6 +498,7 @@ else
 nssobjdir := $(patsubst ../$(subdir),.,$(common-objpfx)nss)
 resolvobjdir := $(patsubst ../$(subdir),.,$(common-objpfx)resolv)
 link-libc = $(common-objpfx)libc.a $(otherlibs) $(gnulib) $(common-objpfx)libc.a $(gnulib)
+link-libc-tests = $(common-objpfx)libc.a $(otherlibs) $(gnulib-tests) $(common-objpfx)libc.a $(gnulib-tests)
 endif
 endif
 
@@ -513,8 +524,43 @@ endif
 
 # The static libraries.
 link-libc-static = -Wl,--start-group $(common-objpfx)libc.a $(static-gnulib) -Wl,--end-group
+link-libc-static-tests = -Wl,--start-group $(common-objpfx)libc.a $(static-gnulib-tests) -Wl,--end-group
 link-libc-bounded = $(common-objpfx)libc_b.a $(gnulib) $(common-objpfx)libc_b.a
 
+# How to link against libgcc.  Some libgcc functions, such as those
+# for "long long" arithmetic or software floating point, can always be
+# built without use of C library headers and do not have any global
+# state so can safely be linked statically into any executable or
+# shared library requiring them; these functions are in libgcc.a.
+# Other functions, relating to exception handling, may require C
+# library headers to build and it may not be safe to have more than
+# one copy of them in a process; these functions are only in
+# libgcc_s.so and libgcc_eh.a.
+#
+# To avoid circular dependencies when bootstrapping, it is desirable
+# to avoid use of libgcc_s and libgcc_eh in building glibc.  Where any
+# glibc functionality (in particular, thread cancellation) requires
+# exception handling, this is implemented through dlopen of libgcc_s
+# to avoid unnecessary dependencies on libgcc_s by programs not using
+# that functionality; executables built with glibc do not use
+# exception handling other than through thread cancellation.
+#
+# Undefined references to functions from libgcc_eh or libgcc_s may
+# arise for code built with -fexceptions.  In the case of statically
+# linked programs installed by glibc, unwinding will never actually
+# occur at runtime and the use of elf/static-stubs.c to resolve these
+# references is safe.  In the case of statically linked test programs
+# and test programs built with -fexceptions, unwinding may occur in
+# some cases and it is preferable to link with libgcc_eh or libgcc_s
+# so that the testing is as similar as possible to how programs will
+# be built with the installed glibc.
+#
+# Some architectures have architecture-specific systems for exception
+# handling that may involve undefined references to
+# architecture-specific functions.  On those architectures,
+# gnulib-arch and static-gnulib-arch may be defined in sysdeps
+# makefiles to use additional libraries for linking executables and
+# shared libraries built by glibc.
 ifndef gnulib
 ifneq ($(have-cc-with-libunwind),yes)
   libunwind =
@@ -522,8 +568,12 @@ else
   libunwind = -lunwind
 endif
 libgcc_eh := -Wl,--as-needed -lgcc_s $(libunwind) -Wl,--no-as-needed
-gnulib := -lgcc $(libgcc_eh)
-static-gnulib := -lgcc -lgcc_eh $(libunwind)
+gnulib-arch =
+gnulib = -lgcc $(gnulib-arch)
+gnulib-tests := -lgcc $(libgcc_eh)
+static-gnulib-arch =
+static-gnulib = -lgcc $(static-gnulib-arch)
+static-gnulib-tests := -lgcc -lgcc_eh $(libunwind)
 libc.so-gnulib := -lgcc
 endif
 +preinit = $(addprefix $(csu-objpfx),crti.o)
diff --git a/Rules b/Rules
index 3c61a29..17d938e 100644
--- a/Rules
+++ b/Rules
@@ -1,5 +1,4 @@
-# Copyright (C) 1991-2000,2002,2003,2004,2005,2006,2011
-#	Free Software Foundation, Inc.
+# Copyright (C) 1991-2012 Free Software Foundation, Inc.
 # This file is part of the GNU C Library.
 
 # The GNU C Library is free software; you can redistribute it and/or
@@ -103,29 +102,46 @@ xtests: tests $(xtests:%=$(objpfx)%.out) $(xtests-bp.out)
 endif
 
 ifeq ($(build-programs),yes)
-binaries-all = $(others) $(sysdep-others) $(tests) $(xtests) $(test-srcs)
-binaries-static = $(others-static) $(tests-static) $(xtests-static)
+binaries-all-notests = $(others) $(sysdep-others)
+binaries-all-tests = $(tests) $(xtests) $(test-srcs)
+binaries-all = $(binaries-all-notests) $(binaries-all-tests)
+binaries-static-notests = $(others-static)
+binaries-static-tests = $(tests-static) $(xtests-static)
+binaries-static = $(binaries-static-notests) $(binaries-static-tests)
 ifeq (yesyes,$(have-fpie)$(build-shared))
 binaries-pie = $(others-pie) $(tests-pie) $(xtests-pie)
 else
 binaries-pie =
 endif
 else
-binaries-all = $(tests) $(xtests) $(test-srcs)
+binaries-all-notests =
+binaries-all-tests = $(tests) $(xtests) $(test-srcs)
+binaries-all = $(binaries-all-tests)
+binaries-static-notests =
+binaries-static-tests =
 binaries-static =
 binaries-pie =
 endif
 
-binaries-shared = $(filter-out $(binaries-pie) $(binaries-static), \
-			       $(binaries-all))
+binaries-shared-tests = $(filter-out $(binaries-pie) $(binaries-static), \
+				     $(binaries-all-tests))
+binaries-shared-notests = $(filter-out $(binaries-pie) $(binaries-static), \
+				       $(binaries-all-notests))
 
-ifneq "$(strip $(binaries-shared))" ""
-$(addprefix $(objpfx),$(binaries-shared)): %: %.o \
+ifneq "$(strip $(binaries-shared-notests))" ""
+$(addprefix $(objpfx),$(binaries-shared-notests)): %: %.o \
   $(sort $(filter $(common-objpfx)lib%,$(link-libc))) \
   $(addprefix $(csu-objpfx),start.o) $(+preinit) $(+postinit)
 	$(+link)
 endif
 
+ifneq "$(strip $(binaries-shared-tests))" ""
+$(addprefix $(objpfx),$(binaries-shared-tests)): %: %.o \
+  $(sort $(filter $(common-objpfx)lib%,$(link-libc))) \
+  $(addprefix $(csu-objpfx),start.o) $(+preinit) $(+postinit)
+	$(+link-tests)
+endif
+
 ifneq "$(strip $(binaries-pie))" ""
 $(addprefix $(objpfx),$(binaries-pie)): %: %.o \
   $(sort $(filter $(common-objpfx)lib%,$(link-libc))) \
@@ -133,13 +149,20 @@ $(addprefix $(objpfx),$(binaries-pie)): %: %.o \
 	$(+link-pie)
 endif
 
-ifneq "$(strip $(binaries-static))" ""
-$(addprefix $(objpfx),$(binaries-static)): %: %.o \
+ifneq "$(strip $(binaries-static-notests))" ""
+$(addprefix $(objpfx),$(binaries-static-notests)): %: %.o \
   $(sort $(filter $(common-objpfx)lib%,$(link-libc-static))) \
   $(addprefix $(csu-objpfx),start.o) $(+preinit) $(+postinit)
 	$(+link-static)
 endif
 
+ifneq "$(strip $(binaries-static-tests))" ""
+$(addprefix $(objpfx),$(binaries-static-tests)): %: %.o \
+  $(sort $(filter $(common-objpfx)lib%,$(link-libc-static-tests))) \
+  $(addprefix $(csu-objpfx),start.o) $(+preinit) $(+postinit)
+	$(+link-static-tests)
+endif
+
 ifeq ($(build-bounded),yes)
 binaries-bounded = $(addsuffix -bp,$(tests) $(xtests) $(test-srcs))
 $(addprefix $(objpfx),$(binaries-bounded)): %-bp: %.ob \
diff --git a/elf/Makefile b/elf/Makefile
index 0c26ce5..9054199 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -71,6 +71,8 @@ others		= sprof sln pldd
 install-bin	= sprof pldd
 others-static   = sln
 install-rootsbin = sln
+sln-modules	:= static-stubs
+extra-objs	+= $(sln-modules:=.o)
 
 ifeq (yes,$(use-ldconfig))
 ifeq (yes,$(build-shared))
@@ -78,7 +80,7 @@ others-static	+= ldconfig
 others		+= ldconfig
 install-rootsbin += ldconfig
 
-ldconfig-modules := cache readlib xmalloc xstrdup chroot_canon
+ldconfig-modules := cache readlib xmalloc xstrdup chroot_canon static-stubs
 extra-objs	+= $(ldconfig-modules:=.o)
 endif
 endif
@@ -411,6 +413,8 @@ $(objpfx)ldd: ldd.bash.in $(common-objpfx)soversions.mk \
 
 $(objpfx)sprof: $(libdl)
 
+$(objpfx)sln: $(sln-modules:%=$(objpfx)%.o)
+
 $(objpfx)ldconfig: $(ldconfig-modules:%=$(objpfx)%.o)
 
 $(objpfx)pldd: $(pldd-modules:%=$(objpfx)%.o)
diff --git a/elf/static-stubs.c b/elf/static-stubs.c
new file mode 100644
index 0000000..6c5eebc
--- /dev/null
+++ b/elf/static-stubs.c
@@ -0,0 +1,46 @@
+/* Stub implementations of functions to link into statically linked
+   programs without needing libgcc_eh.
+   Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+/* Avoid backtrace (and so _Unwind_Backtrace) dependencies from
+   sysdeps/unix/sysv/linux/libc_fatal.c.  */
+#include <sysdeps/posix/libc_fatal.c>
+
+#include <stdlib.h>
+#include <unwind.h>
+
+/* These programs do not use thread cancellation, so _Unwind_Resume
+   and the personality routine are never actually called.  */
+
+void
+_Unwind_Resume (struct _Unwind_Exception *exc __attribute__ ((unused)))
+{
+  abort ();
+}
+
+_Unwind_Reason_Code
+__gcc_personality_v0 (int version __attribute__ ((unused)),
+		      _Unwind_Action actions __attribute__ ((unused)),
+		      _Unwind_Exception_Class exception_class
+		      __attribute__ ((unused)),
+		      struct _Unwind_Exception *ue_header
+		      __attribute__ ((unused)),
+		      struct _Unwind_Context *context __attribute__ ((unused)))
+{
+  abort ();
+}


-- 
Joseph S. Myers
joseph@codesourcery.com


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