[Xen-devel] [PATCH] x86-64: suppress some unneeded side effects of -fPIC

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

Full PIC mode isn't needed for Xen, namely is there no need to access data
objects via the GOT or call functions through the PLT. Adding
-fvisibility=hidden (if the compiler supports it) helps, although it doesn't do
as good a job as would be desired (I'm in talks with our compiler guys to
understand why).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

Index: 2006-09-11/xen/arch/x86/Rules.mk
===================================================================
--- 2006-09-11.orig/xen/arch/x86/Rules.mk       2006-08-21 18:02:23.000000000 
+0200
+++ 2006-09-11/xen/arch/x86/Rules.mk    2006-09-12 17:32:14.000000000 +0200
@@ -11,6 +11,23 @@ HAS_VGA  := y
 pae ?= n
 supervisor_mode_kernel ?= n
 
+# Test for at least GCC v3.2.x.
+gcc-ver = $(shell $(CC) -dumpversion | sed -e 's/^\(.\)\.\(.\)\.\(.\)/\$(1)/')
+ifeq ($(call gcc-ver,1),1)
+$(error gcc-1.x.x unsupported - upgrade to at least gcc-3.2.x)
+endif
+ifeq ($(call gcc-ver,1),2)
+$(error gcc-2.x.x unsupported - upgrade to at least gcc-3.2.x)
+endif
+ifeq ($(call gcc-ver,1),3)
+ifeq ($(call gcc-ver,2),0)
+$(error gcc-3.0.x unsupported - upgrade to at least gcc-3.2.x)
+endif
+ifeq ($(call gcc-ver,2),1)
+$(error gcc-3.1.x unsupported - upgrade to at least gcc-3.2.x)
+endif
+endif
+
 CFLAGS  += -nostdinc -fno-builtin -fno-common -fno-strict-aliasing
 CFLAGS  += -iwithprefix include -Werror -Wno-pointer-arith -pipe
 CFLAGS  += -I$(BASEDIR)/include 
@@ -41,6 +58,9 @@ endif
 
 ifeq ($(TARGET_SUBARCH),x86_64)
 CFLAGS  += -mno-red-zone -fpic -fno-reorder-blocks
+ifneq ($(call gcc-ver,1),3)
+CFLAGS  += -fvisibility=hidden
+endif
 CFLAGS  += -fno-asynchronous-unwind-tables
 LDFLAGS += -m elf_x86_64
 x86_32 := n
@@ -50,20 +70,3 @@ endif
 HDRS += $(wildcard $(BASEDIR)/include/asm-x86/hvm/*.h)
 HDRS += $(wildcard $(BASEDIR)/include/asm-x86/hvm/svm/*.h)
 HDRS += $(wildcard $(BASEDIR)/include/asm-x86/hvm/vmx/*.h)
-
-# Test for at least GCC v3.2.x.
-gcc-ver = $(shell $(CC) -dumpversion | sed -e 's/^\(.\)\.\(.\)\.\(.\)/\$(1)/')
-ifeq ($(call gcc-ver,1),1)
-$(error gcc-1.x.x unsupported - upgrade to at least gcc-3.2.x)
-endif
-ifeq ($(call gcc-ver,1),2)
-$(error gcc-2.x.x unsupported - upgrade to at least gcc-3.2.x)
-endif
-ifeq ($(call gcc-ver,1),3)
-ifeq ($(call gcc-ver,2),0)
-$(error gcc-3.0.x unsupported - upgrade to at least gcc-3.2.x)
-endif
-ifeq ($(call gcc-ver,2),1)
-$(error gcc-3.1.x unsupported - upgrade to at least gcc-3.2.x)
-endif
-endif


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