x86/ftrace, x86/asm: Kill ftrace_caller_end label

One of ftrace_caller_end and ftrace_return is redundant so unify them.
Rename ftrace_return to ftrace_epilogue to mean that everything after
that label represents, like an afterword, work which happens *after* the
ftrace call, e.g., the function graph tracer for one.

Steve wants this to rather mean "[a]n event which reflects meaningfully
on a recently ended conflict or struggle." I can imagine that ftrace can
be a struggle sometimes.

Anyway, beef up the comment about the code contents and layout before
ftrace_epilogue label.

Signed-off-by: Borislav Petkov <[e-mail]>
Reviewed-by: Steven Rostedt <[e-mail]>
Cc: Andy Lutomirski <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Brian Gerst <[e-mail]>
Cc: Denys Vlasenko <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/kernel/ftrace.c

···
 #endif
 
 /* Defined as markers to the end of the ftrace default trampolines */
-extern void ftrace_caller_end(void);
 extern void ftrace_regs_caller_end(void);
-extern void ftrace_return(void);
+extern void ftrace_epilogue(void);
 extern void ftrace_caller_op_ptr(void);
 extern void ftrace_regs_caller_op_ptr(void);
 
···
 		op_offset = (unsigned long)ftrace_regs_caller_op_ptr;
 	} else {
 		start_offset = (unsigned long)ftrace_caller;
-		end_offset = (unsigned long)ftrace_caller_end;
+		end_offset = (unsigned long)ftrace_epilogue;
 		op_offset = (unsigned long)ftrace_caller_op_ptr;
 	}
 
···
 
 	/*
 	 * Allocate enough size to store the ftrace_caller code,
-	 * the jmp to ftrace_return, as well as the address of
+	 * the jmp to ftrace_epilogue, as well as the address of
 	 * the ftrace_ops this trampoline is used for.
 	 */
 	trampoline = alloc_tramp(size + MCOUNT_INSN_SIZE + sizeof(void *));
···
 
 	ip = (unsigned long)trampoline + size;
 
-	/* The trampoline ends with a jmp to ftrace_return */
-	jmp = ftrace_jmp_replace(ip, (unsigned long)ftrace_return);
+	/* The trampoline ends with a jmp to ftrace_epilogue */
+	jmp = ftrace_jmp_replace(ip, (unsigned long)ftrace_epilogue);
 	memcpy(trampoline + size, jmp, MCOUNT_INSN_SIZE);
 
 	/*

arch/x86/kernel/mcount_64.S

···
 	restore_mcount_regs
 
 	/*
-	 * The copied trampoline must call ftrace_return as it
+	 * The copied trampoline must call ftrace_epilogue as it
 	 * still may need to call the function graph tracer.
+	 *
+	 * The code up to this label is copied into trampolines so
+	 * think twice before adding any new code or changing the
+	 * layout here.
 	 */
-GLOBAL(ftrace_caller_end)
-
-GLOBAL(ftrace_return)
+GLOBAL(ftrace_epilogue)
 
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 GLOBAL(ftrace_graph_call)
···
 	popfq
 
 	/*
-	 * As this jmp to ftrace_return can be a short jump
+	 * As this jmp to ftrace_epilogue can be a short jump
 	 * it must not be copied into the trampoline.
 	 * The trampoline will add the code to jump
 	 * to the return.
 	 */
 GLOBAL(ftrace_regs_caller_end)
 
-	jmp ftrace_return
+	jmp ftrace_epilogue
 
 END(ftrace_regs_caller)