s390/vdso: Add CFI for RA register to asm macro vdso_func

The return-address (RA) register r14 is specified as volatile in the
s390x ELF ABI [1]. Nevertheless proper CFI directives must be provided
for an unwinder to restore the return address, if the RA register
value is changed from its value at function entry, as it is the case.

[1]: s390x ELF ABI, https://github.com/IBM/s390x-abi/releases

Fixes: 4bff8cb5 ("s390: convert to GENERIC_VDSO")
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/include/asm/dwarf.h

@@ -9,6 +9,7 @@
 #define CFI_DEF_CFA_OFFSET	.cfi_def_cfa_offset
 #define CFI_ADJUST_CFA_OFFSET	.cfi_adjust_cfa_offset
 #define CFI_RESTORE		.cfi_restore
+#define CFI_REL_OFFSET		.cfi_rel_offset
 
 #ifdef CONFIG_AS_CFI_VAL_OFFSET
 #define CFI_VAL_OFFSET		.cfi_val_offset

arch/s390/kernel/vdso64/vdso_user_wrapper.S

@@ -24,8 +24,10 @@ __kernel_\func:
 	CFI_DEF_CFA_OFFSET (STACK_FRAME_OVERHEAD + WRAPPER_FRAME_SIZE)
 	CFI_VAL_OFFSET 15, -STACK_FRAME_OVERHEAD
 	stg	%r14,STACK_FRAME_OVERHEAD(%r15)
+	CFI_REL_OFFSET 14, STACK_FRAME_OVERHEAD
 	brasl	%r14,__s390_vdso_\func
 	lg	%r14,STACK_FRAME_OVERHEAD(%r15)
+	CFI_RESTORE 14
 	aghi	%r15,WRAPPER_FRAME_SIZE
 	CFI_DEF_CFA_OFFSET STACK_FRAME_OVERHEAD
 	CFI_RESTORE 15