x86 vDSO: use vdso-syms.lds

This patch changes the kernel's references to addresses in the vDSO image
to be based on the symbols defined by vdso-syms.lds instead of the old
vdso-syms.o symbols.  This is all wrapped up in a macro defined by the new
asm-x86/vdso.h header; that's the only place in the kernel source that has
to know the details of the scheme for getting vDSO symbol values.

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>

arch/x86/vdso/Makefile

@@ -3,8 +3,7 @@
 #
 
 # files to link into the vdso
-# vdso-start.o has to be first
-vobjs-y := vdso-start.o vdso-note.o vclock_gettime.o vgetcpu.o vvar.o
+vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o vvar.o
 
 # files to link into kernel
 obj-y := vma.o vdso.o vdso-syms.o

arch/x86/vdso/vma.c

@@ -11,23 +11,20 @@
 #include <asm/vsyscall.h>
 #include <asm/vgtod.h>
 #include <asm/proto.h>
-#include "voffset.h"
+#include <asm/vdso.h>
 
-int vdso_enabled = 1;
-
-#define VEXTERN(x) extern typeof(__ ## x) *vdso_ ## x;
-#include "vextern.h"
+#include "vextern.h"		/* Just for VMAGIC.  */
 #undef VEXTERN
 
-extern char vdso_kernel_start[], vdso_start[], vdso_end[];
+int vdso_enabled = 1;
+
+extern char vdso_start[], vdso_end[];
 extern unsigned short vdso_sync_cpuid;
 
 struct page **vdso_pages;
 
-static inline void *var_ref(void *vbase, char *var, char *name)
+static inline void *var_ref(void *p, char *name)
 {
-	unsigned offset = var - &vdso_kernel_start[0] + VDSO_TEXT_OFFSET;
-	void *p = vbase + offset;
 	if (*(void **)p != (void *)VMAGIC) {
 		printk("VDSO: variable %s broken\n", name);
 		vdso_enabled = 0;
@@ -62,9 +59,8 @@ static int __init init_vdso_vars(void)
 		vdso_enabled = 0;
 	}
 
-#define V(x) *(typeof(x) *) var_ref(vbase, (char *)RELOC_HIDE(&x, 0), #x)
 #define VEXTERN(x) \
-	V(vdso_ ## x) = &__ ## x;
+	*(typeof(__ ## x) **) var_ref(VDSO64_SYMBOL(vbase, x), #x) = &__ ## x;
 #include "vextern.h"
 #undef VEXTERN
 	return 0;

include/asm-x86/vdso.h

@@ -0,0 +1,14 @@
+#ifndef _ASM_X86_VDSO_H
+#define _ASM_X86_VDSO_H	1
+
+extern const char VDSO64_PRELINK[];
+
+/*
+ * Given a pointer to the vDSO image, find the pointer to VDSO64_name
+ * as that symbol is defined in the vDSO sources or linker script.
+ */
+#define VDSO64_SYMBOL(base, name) ({		\
+	extern const char VDSO64_##name[];	\
+	(void *) (VDSO64_##name - VDSO64_PRELINK + (unsigned long) (base)); })
+
+#endif	/* asm-x86/vdso.h */