ARM: vdso: Remove assembly for datapage access

vdso/datapage.h provides a hidden declaration for _vdso_data.
When using it the compiler will automatically generate PC-relative
accesses which avoids the need for a custom assembly-based accessor.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20241010-vdso-generic-base-v1-7-b64f0842d512@linutronix.de

Author: t-8ch

arch/arm/include/asm/vdso/gettimeofday.h

@@ -15,8 +15,6 @@
 
 #define VDSO_HAS_CLOCK_GETRES		1
 
-extern struct vdso_data *__get_datapage(void);
-
 static __always_inline int gettimeofday_fallback(
 				struct __kernel_old_timeval *_tv,
 				struct timezone *_tz)
@@ -139,7 +137,7 @@ static __always_inline u64 __arch_get_hw_counter(int clock_mode,
 
 static __always_inline const struct vdso_data *__arch_get_vdso_data(void)
 {
-	return __get_datapage();
+	return _vdso_data;
 }
 
 #endif /* !__ASSEMBLY__ */

arch/arm/vdso/Makefile

@@ -5,7 +5,7 @@ include $(srctree)/lib/vdso/Makefile
 
 hostprogs := vdsomunge
 
-obj-vdso := vgettimeofday.o datapage.o note.o
+obj-vdso := vgettimeofday.o note.o
 
 # Build rules
 targets := $(obj-vdso) vdso.so vdso.so.dbg vdso.so.raw vdso.lds

arch/arm/vdso/datapage.S

@@ -11,6 +11,7 @@
  */
 
 #include <linux/const.h>
+#include <asm/asm-offsets.h>
 #include <asm/page.h>
 #include <asm/vdso.h>
 
@@ -19,7 +20,7 @@ OUTPUT_ARCH(arm)
 
 SECTIONS
 {
-	PROVIDE(_start = .);
+	PROVIDE(_vdso_data = . - VDSO_DATA_SIZE);
 
 	. = SIZEOF_HEADERS;