This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [PATCH] Avoid an extra branch to PLT for -z now
- From: "H.J. Lu" <hjl dot tools at gmail dot com>
- To: Roland McGrath <roland at hack dot frob dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Tue, 24 May 2016 09:26:03 -0700
- Subject: Re: [PATCH] Avoid an extra branch to PLT for -z now
- Authentication-results: sourceware.org; auth=none
- References: <20160504181716 dot GA21077 at intel dot com> <20160520222916 dot F28972C3D3D at topped-with-meat dot com>
On Fri, May 20, 2016 at 3:29 PM, Roland McGrath <roland@hack.frob.com> wrote:
>> * config.h.in (BIND_NOW): New.
>> * configure.ac (BIND_NOW): New. Defined for --enable-bind-now.
>> * configure: Regenerated.
>> * sysdeps/x86_64/sysdep.h (JUMPTARGET): Defined to indirect
>> branch via the GOT slot.
>
> Should be:
> * sysdeps/x86_64/sysdep.h (JUMPTARGET) [BIND_NOW]:
> Defined to indirect branch via the GOT slot.
>
> Otherwise this seems OK to me.
This is what I checked in.
Thanks.
--
H.J.
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(-)
diff --git a/ChangeLog b/ChangeLog
index 3345a1d..055316f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -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]
diff --git a/config.h.in b/config.h.in
index 0147ba3..2c902b0 100644
--- a/config.h.in
+++ b/config.h.in
@@ -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
diff --git a/configure b/configure
index 8fe5937..19a4829 100755
--- a/configure
+++ b/configure
@@ -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 :
diff --git a/configure.ac b/configure.ac
index 3c766b7..123f0d2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -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.
diff --git a/sysdeps/x86_64/sysdep.h b/sysdeps/x86_64/sysdep.h
index fbe3560..75ac747 100644
--- a/sysdeps/x86_64/sysdep.h
+++ b/sysdeps/x86_64/sysdep.h
@@ -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