x86/unwind: Fix oprofile module link error

When compiling on x86 with CONFIG_OPROFILE=m and CONFIG_FRAME_POINTER=n,
the oprofile module fails to link:

  ERROR: ftrace_graph_ret_addr" [arch/x86/oprofile/oprofile.ko] undefined!

The problem was introduced when oprofile was converted to use the new
x86 unwinder.  When frame pointers are disabled, the "guess" unwinder's
unwind_get_return_address() is an inline function which calls
ftrace_graph_ret_addr(), which is not exported.

Fix it by converting the "guess" version of unwind_get_return_address()
to an exported out-of-line function, just like its frame pointer
counterpart.

Reported-by: Karl Beldan <karl.beldan@gmail.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: ec2ad9c ("oprofile/x86: Convert x86_backtrace() to use the new unwinder")
Link: http://lkml.kernel.org/r/be08d589f6474df78364e081c42777e382af9352.1475731632.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/unwind.h

@@ -23,6 +23,8 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 
 bool unwind_next_frame(struct unwind_state *state);
 
+unsigned long unwind_get_return_address(struct unwind_state *state);
+
 static inline bool unwind_done(struct unwind_state *state)
 {
 	return state->stack_info.type == STACK_TYPE_UNKNOWN;
@@ -48,8 +50,6 @@ unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
 	return state->bp + 1;
 }
 
-unsigned long unwind_get_return_address(struct unwind_state *state);
-
 #else /* !CONFIG_FRAME_POINTER */
 
 static inline
@@ -58,16 +58,6 @@ unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
 	return NULL;
 }
 
-static inline
-unsigned long unwind_get_return_address(struct unwind_state *state)
-{
-	if (unwind_done(state))
-		return 0;
-
-	return ftrace_graph_ret_addr(state->task, &state->graph_idx,
-				     *state->sp, state->sp);
-}
-
 #endif /* CONFIG_FRAME_POINTER */
 
 #endif /* _ASM_X86_UNWIND_H */

arch/x86/kernel/unwind_guess.c

@@ -5,6 +5,16 @@
 #include <asm/stacktrace.h>
 #include <asm/unwind.h>
 
+unsigned long unwind_get_return_address(struct unwind_state *state)
+{
+	if (unwind_done(state))
+		return 0;
+
+	return ftrace_graph_ret_addr(state->task, &state->graph_idx,
+				     *state->sp, state->sp);
+}
+EXPORT_SYMBOL_GPL(unwind_get_return_address);
+
 bool unwind_next_frame(struct unwind_state *state)
 {
 	struct stack_info *info = &state->stack_info;