Document and fix --enable-bind-now [BZ #21015]

diff --git a/INSTALL b/INSTALL
index 55d52c5..0195782 100644
--- a/INSTALL
+++ b/INSTALL
@@ -146,6 +146,12 @@  will be used, and CFLAGS sets optimization options for the compiler.
      of routines called directly from assembler are excluded from this
      protection.
 
+'--enable-bind-now'
+     Disable lazy binding for installed shared objects.  This provides
+     additional security hardening because it enables full RELRO and a
+     read-only global offset table (GOT), at the cost of slightly
+     increased program load times.
+
 '--enable-pt_chown'
      The file 'pt_chown' is a helper binary for 'grantpt' (*note
      Pseudo-Terminals: Allocation.) that is installed setuid root to fix
diff --git a/Makeconfig b/Makeconfig
index 97a15b5..1c81511 100644
--- a/Makeconfig
+++ b/Makeconfig
@@ -386,6 +386,13 @@  LDFLAGS.so += $(hashstyle-LDFLAGS)
 LDFLAGS-rtld += $(hashstyle-LDFLAGS)
 endif
 
+# If lazy relocations are disabled, add the -z now flag.  Use
+# LDFLAGS-lib.so instead of LDFLAGS.so, to avoid adding the flag to
+# test modules.
+ifeq ($(bind-now),yes)
+LDFLAGS-lib.so += -Wl,-z,now
+endif
+
 # Command to run after every final link (executable or shared object).
 # This is invoked with $(call after-link,...), so it should operate on
 # the file $1.  This can be set to do some sort of post-processing on
diff --git a/Makerules b/Makerules
index e9194e5..7f0eef8 100644
--- a/Makerules
+++ b/Makerules
@@ -588,7 +588,7 @@  $(LINK.o) -shared -static-libgcc -Wl,-O1 $(sysdep-LDFLAGS) \
 	  $(extra-B-$(@F:lib%.so=%).so) -B$(csu-objpfx) \
 	  $(extra-B-$(@F:lib%.so=%).so) $(load-map-file) \
 	  -Wl,-soname=lib$(libprefix)$(@F:lib%.so=%).so$($(@F)-version) \
-	  $(LDFLAGS.so) $(LDFLAGS-$(@F:lib%.so=%).so) \
+	  $(LDFLAGS.so) $(LDFLAGS-lib.so) $(LDFLAGS-$(@F:lib%.so=%).so) \
 	  -L$(subst :, -L,$(rpath-link)) -Wl,-rpath-link=$(rpath-link)
 endef
 
@@ -686,10 +686,6 @@  LDFLAGS-c.so = -nostdlib -nostartfiles
 LDLIBS-c.so += $(libc.so-gnulib)
 # Give libc.so an entry point and make it directly runnable itself.
 LDFLAGS-c.so += -e __libc_main
-# If lazy relocation is disabled add the -z now flag.
-ifeq ($(bind-now),yes)
-LDFLAGS-c.so += -Wl,-z,now
-endif
 # Pre-link the objects of libc_pic.a so that we can locally resolve
 # COMMON symbols before we link against ld.so.  This is because ld.so
 # contains some of libc_pic.a already, which will prevent the COMMONs
@@ -1104,7 +1100,8 @@  $(common-objpfx)format.lds: $(..)scripts/output-format.sed \
 ifneq (unknown,$(output-format))
 	echo > $@.new 'OUTPUT_FORMAT($(output-format))'
 else
-	$(LINK.o) -shared $(sysdep-LDFLAGS) $(rtld-LDFLAGS) $(LDFLAGS.so) \
+	$(LINK.o) -shared $(sysdep-LDFLAGS) $(rtld-LDFLAGS) \
+		  $(LDFLAGS.so) $(LDFLAGS-lib.so) \
 		  -x c /dev/null -o $@.so -Wl,--verbose -v 2>&1 \
 	| sed -n -f $< > $@.new
 	test -s $@.new
diff --git a/manual/install.texi b/manual/install.texi
index 2657da1..a3718ef 100644
--- a/manual/install.texi
+++ b/manual/install.texi
@@ -175,6 +175,12 @@  options to detect stack overruns.  Only the dynamic linker and a small
 number of routines called directly from assembler are excluded from this
 protection.
 
+@item --enable-bind-now
+Disable lazy binding for installed shared objects.  This provides
+additional security hardening because it enables full RELRO and a
+read-only global offset table (GOT), at the cost of slightly increased
+program load times.
+
 @pindex pt_chown
 @findex grantpt
 @item --enable-pt_chown
diff --git a/sysdeps/unix/sysv/linux/alpha/localplt.data b/sysdeps/unix/sysv/linux/alpha/localplt.data
index cca17f1..1f0e3b4 100644
--- a/sysdeps/unix/sysv/linux/alpha/localplt.data
+++ b/sysdeps/unix/sysv/linux/alpha/localplt.data
@@ -20,7 +20,7 @@  libc.so: free + RELA R_ALPHA_GLOB_DAT
 libc.so: malloc + RELA R_ALPHA_GLOB_DAT
 libc.so: memalign + RELA R_ALPHA_GLOB_DAT
 libc.so: realloc + RELA R_ALPHA_GLOB_DAT
-libm.so: matherr
+libm.so: matherr + RELA R_ALPHA_GLOB_DAT
 # We used to offer inline functions that used this, so it must be exported.
 # Ought to reorg things such that carg isn't thus forced to use a plt.
 libm.so: __atan2
diff --git a/sysdeps/unix/sysv/linux/i386/localplt.data b/sysdeps/unix/sysv/linux/i386/localplt.data
index 2c25849..8ea4333 100644
--- a/sysdeps/unix/sysv/linux/i386/localplt.data
+++ b/sysdeps/unix/sysv/linux/i386/localplt.data
@@ -6,7 +6,7 @@  libc.so: free + REL R_386_GLOB_DAT
 libc.so: malloc + REL R_386_GLOB_DAT
 libc.so: memalign + REL R_386_GLOB_DAT
 libc.so: realloc + REL R_386_GLOB_DAT
-libm.so: matherr
+libm.so: matherr + REL R_386_GLOB_DAT
 # The main malloc is interposed into the dynamic linker, for
 # allocations after the initial link (when dlopen is used).
 ld.so: malloc + REL R_386_GLOB_DAT
diff --git a/sysdeps/x86_64/localplt.data b/sysdeps/x86_64/localplt.data
index 014a9f4..a1840cf 100644
--- a/sysdeps/x86_64/localplt.data
+++ b/sysdeps/x86_64/localplt.data
@@ -8,7 +8,7 @@  libc.so: free + RELA R_X86_64_GLOB_DAT
 libc.so: malloc + RELA R_X86_64_GLOB_DAT
 libc.so: memalign + RELA R_X86_64_GLOB_DAT
 libc.so: realloc + RELA R_X86_64_GLOB_DAT
-libm.so: matherr
+libm.so: matherr + RELA R_X86_64_GLOB_DAT
 # The main malloc is interposed into the dynamic linker, for
 # allocations after the initial link (when dlopen is used).
 ld.so: malloc + RELA R_X86_64_GLOB_DAT