x86 vDSO: generate vdso-syms.lds

This patch adds a new way of extracting symbols from the built vDSO image.
This is much simpler and less fragile than using ld -R; it removes the
need to control the DSO layout quite so exactly.  I was clearly unduly
distracted by clever ld uses when I did the original vDSO implementation.

Signed-off-by: Roland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 24 insertions, 0 deletions

diff --git a/arch/x86/vdso/Makefile b/arch/x86/vdso/Makefile
index e7bff0fbac23..d8200adae9fa 100644
--- a/arch/x86/vdso/Makefile
+++ b/arch/x86/vdso/Makefile
@@ -55,6 +55,20 @@ SYSCFLAGS_vdso-syms.o = -r -d
 $(obj)/vdso-syms.o: $(src)/vdso.lds $(vobjs) FORCE
         $(call if_changed,syscall)
 
+targets += vdso-syms.lds
+obj-y += vdso-syms.lds
+
+#
+# Match symbols in the DSO that look like VDSO*; produce a file of constants.
+#
+sed-vdsosym := -e 's/^00*/0/' \
+        -e 's/^\([0-9a-fA-F]*\) . \(VDSO[a-zA-Z0-9_]*\)$$/\2 = 0x\1;/p'
+quiet_cmd_vdsosym = VDSOSYM $@
+      cmd_vdsosym = $(NM) $< | sed -n $(sed-vdsosym) | LC_ALL=C sort > $@
+
+$(obj)/%-syms.lds: $(obj)/%.so.dbg FORCE
+        $(call if_changed,vdsosym)
+
 quiet_cmd_vdso_install = INSTALL $@
       cmd_vdso_install = cp $(obj)/$@.dbg $(MODLIB)/vdso/$@
 vdso.so:
diff --git a/arch/x86/vdso/vdso.lds.S b/arch/x86/vdso/vdso.lds.S
index 667d3245d972..d40d0e906190 100644
--- a/arch/x86/vdso/vdso.lds.S
+++ b/arch/x86/vdso/vdso.lds.S
@@ -8,6 +8,16 @@
 
 #define VDSO_PRELINK 0xffffffffff700000
 
+/*
+ * Symbols we define here called VDSO* get their values into vdso-syms.lds
+ * and become visible to the kernel itself.
+ */
+VDSO64_PRELINK = VDSO_PRELINK;
+
+#define VEXTERN(x)      VDSO64_ ## x = vdso_ ## x;
+#include "vextern.h"
+#undef  VEXTERN
+
 SECTIONS
 {
   . = VDSO_PRELINK + SIZEOF_HEADERS;