[RFC][PATCH v12 4/8] Add DT_GNU_FLAGS_1/DF_GNU_1_UNIQUE to glibc DSOs (bug 22745)

["Vivek Das Mohapatra via Libc-alpha" <libc-alpha@sourceware.org>]

libc.so, libpthread.so etc should have the new unique-dso-by-default
flag set to allow dlmopen to work better (libc et al instance shared
by default when DSOs dlmopened into a new namespace).
---
 Makeconfig                |  3 +++
 Makerules                 | 18 ++++++++++++++++-
 config.make.in            |  1 +
 configure                 | 42 ++++++++++++++++++++++++++++++++++++---
 configure.ac              | 31 ++++++++++++++++++++++++++---
 elf/Makefile              |  3 +++
 elf/dynamic-notes.c       |  4 ++++
 extra-lib.mk              |  3 +++
 htl/Makefile              |  3 +++
 iconvdata/Makefile        |  3 +++
 iconvdata/extra-module.mk |  4 ++++
 nptl/Makefile             |  7 ++++++-
 12 files changed, 114 insertions(+), 8 deletions(-)
 create mode 100644 elf/dynamic-notes.c

diff --git a/Makeconfig b/Makeconfig
index efc7351d71..baa893840e 100644
--- a/Makeconfig
+++ b/Makeconfig
@@ -398,6 +398,9 @@ LDFLAGS-lib.so += -Wl,-z,now
 # Extra flags for dynamically linked non-test main programs.
 link-extra-flags += -Wl,-z,now
 endif
+ifeq ($(ld-zunique),yes)
+LDFLAGS-lib.so += -Wl,-z,unique
+endif
 
 # Command to run after every final link (executable or shared object).
 # This is invoked with $(call after-link,...), so it should operate on
diff --git a/Makerules b/Makerules
index 596fa68376..66c1251754 100644
--- a/Makerules
+++ b/Makerules
@@ -581,7 +581,8 @@ $(common-objpfx)shlib.lds: $(common-objpfx)config.make $(..)Makerules
 		 PROVIDE(__start___libc_IO_vtables = .);\
 		 __libc_IO_vtables : { *(__libc_IO_vtables) }\
 		 PROVIDE(__stop___libc_IO_vtables = .);\
-		 /DISCARD/ : { *(.gnu.glibc-stub.*) }@'
+		 /DISCARD/ : { *(.gnu.glibc-stub.*) }@' \
+	      -e 's/^.*\*(\.dynamic).*$$/   .dynamic : { *dynamic-notes.os(.dynamic) *(.dynamic) }/'
 	test -s $@T
 	mv -f $@T $@
 common-generated += shlib.lds
@@ -636,6 +637,16 @@ build-shlib-objlist = $(build-module-helper-objlist) \
 # Also omits crti.o and crtn.o, which we do not want
 # since we define our own `.init' section specially.
 LDFLAGS-c.so = -nostdlib -nostartfiles
+
+# The stub dynamic-notes.os should not have weak/undefined symbol magic in it.
+# It's not really part of the internals, rather it is a vector for linker magic
+# which we need when the linker isn't new enough:
+%/dynamic-notes.os: CPPFLAGS += -UMODULE_NAME
+
+ifeq ($(ld-zunique),yes)
+LDFLAGS-c.so += -Wl,-z,unique
+endif
+
 # But we still want to link libc.so against $(libc.so-gnulib).
 LDLIBS-c.so += $(libc.so-gnulib)
 # Give libc.so an entry point and make it directly runnable itself.
@@ -706,6 +717,11 @@ $(common-objpfx)linkobj/libc.so: $(common-objpfx)linkobj/libc_pic.a \
 	$(build-shlib)
 	$(call after-link,$@)
 
+ifneq ($(ld-zunique),yes)
+$(common-objpfx)libc.so: $(common-objpfx)elf/dynamic-notes.os
+$(common-objpfx)linkobj/libc.so: $(common-objpfx)elf/dynamic-notes.os
+endif
+
 ifeq ($(build-shared),yes)
 $(common-objpfx)libc.so: $(common-objpfx)libc.map
 endif
diff --git a/config.make.in b/config.make.in
index cbf59114b0..8755490c13 100644
--- a/config.make.in
+++ b/config.make.in
@@ -72,6 +72,7 @@ have-cc-with-libunwind = @libc_cv_cc_with_libunwind@
 fno-unit-at-a-time = @fno_unit_at_a_time@
 bind-now = @bindnow@
 have-hash-style = @libc_cv_hashstyle@
+ld-zunique = @ld_zunique@
 use-default-link = @use_default_link@
 have-cxx-thread_local = @libc_cv_cxx_thread_local@
 have-loop-to-function = @libc_cv_cc_loop_to_function@
diff --git a/configure b/configure
index 9619c10991..a53243a178 100755
--- a/configure
+++ b/configure
@@ -625,6 +625,7 @@ libc_cv_cc_nofma
 libc_cv_mtls_dialect_gnu2
 fno_unit_at_a_time
 libc_cv_has_glob_dat
+ld_zunique
 libc_cv_hashstyle
 libc_cv_fpie
 libc_cv_z_execstack
@@ -6074,9 +6075,38 @@ fi
 $as_echo "$libc_cv_hashstyle" >&6; }
 
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker DT_GNU_FLAGS_1/ DF_GNU_1_UNIQUE support" >&5
+$as_echo_n "checking for linker DT_GNU_FLAGS_1/ DF_GNU_1_UNIQUE support... " >&6; }
+if ${libc_cv_ld_zunique+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat > conftest.ld.c <<\EOF
+int x (void) { return 0; }
+EOF
+
+libc_cv_ld_zunique=no;
+
+if { ac_try='${CC-cc} -Wl,--fatal-warnings -Wl,-z,unique -shared -o conftest.ld.so conftest.ld.c'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }
+then
+  libc_cv_ld_zunique=yes
+fi;
+ld_zunique=$libc_cv_ld_zunique
+rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_ld_zunique" >&5
+$as_echo "$libc_cv_ld_zunique" >&6; }
+
+
 # The linker's default -shared behavior is good enough if it
 # does these things that our custom linker scripts ensure that
-# all allocated NOTE sections come first.
+# all allocated NOTE sections come first AND it understands
+# -z unique should result in DT_GNU_FLAGS_1/DF_GNU_1_UNIQUE
+# sections in its output.
 if test "$use_default_link" = default; then
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for sufficient default -shared layout" >&5
 $as_echo_n "checking for sufficient default -shared layout... " >&6; }
@@ -6119,10 +6149,16 @@ EOF
       esac
       shift 2
     done
-    case "$libc_seen_a$libc_seen_b" in
-    yesyes)
+    case "$libc_seen_a$libc_seen_b$libc_cv_ld_zunique" in
+    yesyesyes)
       libc_cv_use_default_link=yes
       ;;
+    yesyesno)
+      echo >&5 "\
+shared layout from:
+$ac_try
+is OK but -Wl,-z,unique is unsupported so linker scripts are required"
+      ;;
     *)
       echo >&5 "\
 $libc_seen_a$libc_seen_b from:
diff --git a/configure.ac b/configure.ac
index 34ecbba540..9369bcbebe 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1372,9 +1372,28 @@ fi
 rm -f conftest*])
 AC_SUBST(libc_cv_hashstyle)
 
+AC_CACHE_CHECK([for linker DT_GNU_FLAGS_1/ DF_GNU_1_UNIQUE support],
+                libc_cv_ld_zunique, [dnl
+cat > conftest.ld.c <<\EOF
+int x (void) { return 0; }
+EOF
+
+libc_cv_ld_zunique=no;
+
+if AC_TRY_COMMAND([dnl
+${CC-cc} -Wl,--fatal-warnings -Wl,-z,unique -shared -o conftest.ld.so conftest.ld.c])
+then
+  libc_cv_ld_zunique=yes
+fi;
+ld_zunique=$libc_cv_ld_zunique
+rm -f conftest*])
+AC_SUBST(ld_zunique)
+
 # The linker's default -shared behavior is good enough if it
 # does these things that our custom linker scripts ensure that
-# all allocated NOTE sections come first.
+# all allocated NOTE sections come first AND it understands
+# -z unique should result in DT_GNU_FLAGS_1/DF_GNU_1_UNIQUE
+# sections in its output.
 if test "$use_default_link" = default; then
   AC_CACHE_CHECK([for sufficient default -shared layout],
 		  libc_cv_use_default_link, [dnl
@@ -1410,10 +1429,16 @@ EOF
       esac
       shift 2
     done
-    case "$libc_seen_a$libc_seen_b" in
-    yesyes)
+    case "$libc_seen_a$libc_seen_b$libc_cv_ld_zunique" in
+    yesyesyes)
       libc_cv_use_default_link=yes
       ;;
+    yesyesno)
+      echo >&AS_MESSAGE_LOG_FD "\
+shared layout from:
+$ac_try
+is OK but -Wl,-z,unique is unsupported so linker scripts are required"
+      ;;
     *)
       echo >&AS_MESSAGE_LOG_FD "\
 $libc_seen_a$libc_seen_b from:
diff --git a/elf/Makefile b/elf/Makefile
index 698a6ab985..9734030c23 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -103,6 +103,9 @@ endif
 
 ifeq (yes,$(build-shared))
 extra-objs	= $(all-rtld-routines:%=%.os) sofini.os interp.os
+ifneq (yes,$(ld-zunique))
+extra-objs      += dynamic-notes.os
+endif
 generated	+= librtld.os dl-allobjs.os ld.so ldd
 install-others	= $(inst_rtlddir)/$(rtld-installed-name)
 install-bin-script = ldd
diff --git a/elf/dynamic-notes.c b/elf/dynamic-notes.c
new file mode 100644
index 0000000000..d0b487e970
--- /dev/null
+++ b/elf/dynamic-notes.c
@@ -0,0 +1,4 @@
+#include <link.h>
+
+const ElfW(Dyn) __dynamic_note __attribute__ ((section (".dynamic"))) =
+  { .d_tag = DT_GNU_FLAGS_1, .d_un.d_val = DF_GNU_1_UNIQUE };
diff --git a/extra-lib.mk b/extra-lib.mk
index 72f8d2e1df..9051958ec0 100644
--- a/extra-lib.mk
+++ b/extra-lib.mk
@@ -101,6 +101,9 @@ $(objpfx)$(lib).so: $(firstword $($(lib)-map) \
 				$(addprefix $(common-objpfx), \
 					    $(filter $(lib).map, \
 						     $(version-maps))))
+ifneq ($(ld-zunique),yes)
+$(objpfx)$(lib).so: $(common-objpfx)/elf/dynamic-notes.os
+endif
 endif
 
 endif
diff --git a/htl/Makefile b/htl/Makefile
index cf9d12fc12..c2a25dcd79 100644
--- a/htl/Makefile
+++ b/htl/Makefile
@@ -203,6 +203,9 @@ libc-link.so = $(common-objpfx)libc.so
 
 extra-B-pthread.so = -B$(common-objpfx)htl/
 LDFLAGS-pthread.so = -Wl,--enable-new-dtags,-z,nodelete,-z,initfirst
+ifeq ($(ld-zunique),yes)
+LDFLAGS-pthread.so += -Wl,-z,unique
+endif
 
 include ../Rules
 
diff --git a/iconvdata/Makefile b/iconvdata/Makefile
index bb3f621b49..4170005322 100644
--- a/iconvdata/Makefile
+++ b/iconvdata/Makefile
@@ -67,6 +67,9 @@ modules	:= ISO8859-1 ISO8859-2 ISO8859-3 ISO8859-4 ISO8859-5		 \
 ifeq ($(bind-now),yes)
 LDFLAGS.so += -Wl,-z,now
 endif
+ifeq ($(ld-zunique),yes)
+LDFLAGS.so += -Wl,-z,unique
+endif
 
 modules.so := $(addsuffix .so, $(modules))
 
diff --git a/iconvdata/extra-module.mk b/iconvdata/extra-module.mk
index ecaf507624..92c3ab4d7b 100644
--- a/iconvdata/extra-module.mk
+++ b/iconvdata/extra-module.mk
@@ -7,6 +7,10 @@ $(objpfx)$(mod).so: $(addprefix $(objpfx),$(addsuffix .os,$($(mod)-routines)))\
 		    $(shlib-lds) $(link-libc-deps)
 	$(build-module-asneeded)
 
+ifneq ($(ld-zunique),yes)
+$(objpfx)$(mod).so: $(common-objpfx)/elf/dynamic-notes.os
+endif
+
 ifneq (,$(extra-modules-left))
 include extra-module.mk
 endif
diff --git a/nptl/Makefile b/nptl/Makefile
index 9b94bfcd31..81353b9455 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -375,7 +375,12 @@ CPPFLAGS-tst-pthread-gdb-attach-static.c := \
 # were launched with an explicit ld.so invocation.
 tst-pthread-gdb-attach-no-pie = yes
 
-tests += tst-cancelx7 tst-cancelx17
+LDFLAGS-pthread.so = -Wl,--enable-new-dtags,-z,nodelete,-z,initfirst
+ifeq ($(ld-zunique),yes)
+LDFLAGS-pthread.so += -Wl,-z,unique
+endif
+
+tests += tst-cancelx7 tst-cancelx17 tst-cleanupx4
 
 ifeq ($(build-shared),yes)
 tests += tst-compat-forwarder tst-audit-threads
-- 
2.20.1