linux-kernel - [PATCH 6/6] x86-64: Turn off -pg and turn on -foptimize-sibling-calls for vDSO

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Message-Id: <72a7cb0d5ec0acfb1e9c008e0a5ccb8fa078803a.1301324270.git.luto@mit.edu>
Date:	Mon, 28 Mar 2011 11:06:46 -0400
From:	Andy Lutomirski <luto@....EDU>
To:	x86@...nel.org
Cc:	linux-kernel@...r.kernel.org, John Stultz <johnstul@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andy Lutomirski <luto@....edu>
Subject: [PATCH 6/6] x86-64: Turn off -pg and turn on -foptimize-sibling-calls for vDSO

The vDSO isn't part of the kernel, so profiling and kernel
backtraces don't really matter.

Signed-off-by: Andy Lutomirski <luto@....edu>
---

This might need a cc-option check for -foptimize-sibling-calls.

 arch/x86/vdso/Makefile |   15 ++++++++++++++-
 1 files changed, 14 insertions(+), 1 deletions(-)

diff --git a/arch/x86/vdso/Makefile b/arch/x86/vdso/Makefile
index b6552b1..7b6df84 100644
--- a/arch/x86/vdso/Makefile
+++ b/arch/x86/vdso/Makefile
@@ -37,11 +37,24 @@ $(obj)/%.so: OBJCOPYFLAGS := -S
 $(obj)/%.so: $(obj)/%.so.dbg FORCE
 	$(call if_changed,objcopy)
 
+#
+# Don't omit frame pointers for ease of userspace debugging, but do
+# optimize sibling calls.
+#
 CFL := $(PROFILING) -mcmodel=small -fPIC -O2 -fasynchronous-unwind-tables -m64 \
-       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector)
+       $(filter -g%,$(KBUILD_CFLAGS)) $(call cc-option, -fno-stack-protector) \
+       -fno-omit-frame-pointer -foptimize-sibling-calls
 
 $(vobjs): KBUILD_CFLAGS += $(CFL)
 
+#
+# vDSO code runs in userspace and -pg doesn't help with profiling anyway.
+#
+CFLAGS_REMOVE_vdso-note.o = -pg
+CFLAGS_REMOVE_vclock_gettime.o = -pg
+CFLAGS_REMOVE_vgetcpu.o = -pg
+CFLAGS_REMOVE_vvar.o = -pg
+
 targets += vdso-syms.lds
 obj-$(VDSO64-y)			+= vdso-syms.lds
 
-- 
1.7.4

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