From 6901def689b5c77465d34f07822989ec67e80c1e Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Tue, 24 May 2016 08:44:10 -0700
Subject: [PATCH] Avoid an extra branch to PLT for -z now
When --enable-bind-now is used to configure glibc build, we can avoid
an extra branch to the PLT entry by using indirect branch via the GOT
slot instead, which is similar to the first instructuon in the PLT
entry. Changes in the shared library sizes in text sections:
Shared library Before (bytes) After (bytes)
libm.so 1060813 1060797
libmvec.so 160881 160805
libpthread.so 94992 94984
librt.so 25064 25048
* config.h.in (BIND_NOW): New.
* configure.ac (BIND_NOW): New. Defined for --enable-bind-now.
* configure: Regenerated.
* sysdeps/x86_64/sysdep.h (JUMPTARGET)[BIND_NOW]: Defined to
indirect branch via the GOT slot.
---
ChangeLog | 8 ++++++++
config.h.in | 3 +++
configure | 4 ++++
configure.ac | 3 +++
sysdeps/x86_64/sysdep.h | 8 ++++++--
5 files changed, 24 insertions(+), 2 deletions(-)
@@ -1,3 +1,11 @@
+2016-05-24 H.J. Lu <hongjiu.lu@intel.com>
+
+ * config.h.in (BIND_NOW): New.
+ * configure.ac (BIND_NOW): New. Defined for --enable-bind-now.
+ * configure: Regenerated.
+ * sysdeps/x86_64/sysdep.h (JUMPTARGET)[BIND_NOW]: Defined to
+ indirect branch via the GOT slot.
+
2016-05-24 Stefan Liebler <stli@linux.vnet.ibm.com>
[BZ #19765]
@@ -87,6 +87,9 @@
include/libc-symbols.h that avoid PLT slots in the shared objects. */
#undef NO_HIDDEN
+/* Define this to disable lazy relocations in DSOs. */
+#undef BIND_NOW
+
/* AArch64 big endian ABI */
#undef HAVE_AARCH64_BE
@@ -3416,6 +3416,10 @@ else
fi
+if test "x$bindnow" = xyes; then
+ $as_echo "#define BIND_NOW 1" >>confdefs.h
+
+fi
# Check whether --enable-static-nss was given.
if test "${enable_static_nss+set}" = set; then :
@@ -231,6 +231,9 @@ AC_ARG_ENABLE([bind-now],
[bindnow=$enableval],
[bindnow=no])
AC_SUBST(bindnow)
+if test "x$bindnow" = xyes; then
+ AC_DEFINE(BIND_NOW)
+fi
dnl On some platforms we cannot use dynamic loading. We must provide
dnl static NSS modules.
@@ -90,9 +90,13 @@ lose: \
#undef JUMPTARGET
#ifdef PIC
-#define JUMPTARGET(name) name##@PLT
+# ifdef BIND_NOW
+# define JUMPTARGET(name) *name##@GOTPCREL(%rip)
+# else
+# define JUMPTARGET(name) name##@PLT
+# endif
#else
-#define JUMPTARGET(name) name
+# define JUMPTARGET(name) name
#endif
/* Local label name for asm code. */
--
2.5.5