s390/vdso: Introduce and use struct stack_frame_vdso_wrapper

Introduce and use struct stack_frame_vdso_wrapper within vdso user wrapper
code.  With this structure it is possible to automatically generate an
asm-offset define which can be used to save and restore the return address
of the calling function.

Also use STACK_FRAME_USER_OVERHEAD instead of STACK_FRAME_OVERHEAD to
document that the code works with user space stack frames with the standard
stack frame layout.

Fixes: aa44433a ("s390: add USER_STACKTRACE support")
Reviewed-by: Jens Remus <jremus@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

arch/s390/include/asm/stacktrace.h

@@ -13,6 +13,11 @@ struct stack_frame_user {
 	unsigned long empty2[4];
 };
 
+struct stack_frame_vdso_wrapper {
+	struct stack_frame_user sf;
+	unsigned long return_address;
+};
+
 struct perf_callchain_entry_ctx;
 
 void arch_stack_walk_user_common(stack_trace_consume_fn consume_entry, void *cookie,

arch/s390/kernel/asm-offsets.c

@@ -66,6 +66,10 @@ int main(void)
 	OFFSET(__SF_SIE_CONTROL_PHYS, stack_frame, sie_control_block_phys);
 	DEFINE(STACK_FRAME_OVERHEAD, sizeof(struct stack_frame));
 	BLANK();
+	DEFINE(STACK_FRAME_USER_OVERHEAD, sizeof(struct stack_frame_user));
+	OFFSET(__SFVDSO_RETURN_ADDRESS, stack_frame_vdso_wrapper, return_address);
+	DEFINE(STACK_FRAME_VDSO_OVERHEAD, sizeof(struct stack_frame_vdso_wrapper));
+	BLANK();
 	/* idle data offsets */
 	OFFSET(__CLOCK_IDLE_ENTER, s390_idle_data, clock_idle_enter);
 	OFFSET(__TIMER_IDLE_ENTER, s390_idle_data, timer_idle_enter);

arch/s390/kernel/vdso64/vdso_user_wrapper.S

@@ -6,8 +6,6 @@
 #include <asm/dwarf.h>
 #include <asm/ptrace.h>
 
-#define WRAPPER_FRAME_SIZE (STACK_FRAME_OVERHEAD+8)
-
 /*
  * Older glibc version called vdso without allocating a stackframe. This wrapper
  * is just used to allocate a stackframe. See
@@ -20,16 +18,16 @@
 	__ALIGN
 __kernel_\func:
 	CFI_STARTPROC
-	aghi	%r15,-WRAPPER_FRAME_SIZE
-	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
+	aghi	%r15,-STACK_FRAME_VDSO_OVERHEAD
+	CFI_DEF_CFA_OFFSET (STACK_FRAME_USER_OVERHEAD + STACK_FRAME_VDSO_OVERHEAD)
+	CFI_VAL_OFFSET 15,-STACK_FRAME_USER_OVERHEAD
+	stg	%r14,__SFVDSO_RETURN_ADDRESS(%r15)
+	CFI_REL_OFFSET 14,__SFVDSO_RETURN_ADDRESS
 	brasl	%r14,__s390_vdso_\func
-	lg	%r14,STACK_FRAME_OVERHEAD(%r15)
+	lg	%r14,__SFVDSO_RETURN_ADDRESS(%r15)
 	CFI_RESTORE 14
-	aghi	%r15,WRAPPER_FRAME_SIZE
-	CFI_DEF_CFA_OFFSET STACK_FRAME_OVERHEAD
+	aghi	%r15,STACK_FRAME_VDSO_OVERHEAD
+	CFI_DEF_CFA_OFFSET STACK_FRAME_USER_OVERHEAD
 	CFI_RESTORE 15
 	br	%r14
 	CFI_ENDPROC