[RFC -tip] x86: introduce ENTRY(KPROBE)_X86 assembly helpers to catch unbalanced declaration

[Cyrill Gorcunov <gorcunov@gmail.com>]

It's usefull to catch unbalanced, missed or mixed declarations of ENTRY and
KPROBES. These macros would help a bit (at least I hope so).

For example the following code would compile without problems

        ENTRY_X86(mcount)
                retq
        END_X86(mcount)

But if you forget and mix the following form

        ENTRY_X86(mcount)
                retq
        END(mcount)

        ENTRY_X86(ftrace_caller)

The assembler will issue the following message:
Error: ENTRY_X86/KPROBE_X86 unbalanced,missed,mixed

Actually the checking is performed at every _X86 macro
so maybe it's good idea to put ENTRY_KPROBE_FINAL_X86
at the end of .S file to be sure you didn't miss anything.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
---
 arch/x86/include/asm/linkage.h |   60 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

Index: linux-2.6.git/arch/x86/include/asm/linkage.h
===================================================================
--- linux-2.6.git.orig/arch/x86/include/asm/linkage.h
+++ linux-2.6.git/arch/x86/include/asm/linkage.h
@@ -57,5 +57,65 @@
 #define __ALIGN_STR ".align 16,0x90"
 #endif
 
+/*
+ * to check ENTRY_X86/END_X86 and
+ * KPROBE_ENTRY_X86/KPROBE_END_X86
+ * unbalanced-missed-mixed appearance
+ */
+#define __set_entry_x86		.set ENTRY_X86_IN, 0
+#define __unset_entry_x86	.set ENTRY_X86_IN, 1
+#define __set_kprobe_x86	.set KPROBE_X86_IN, 0
+#define __unset_kprobe_x86	.set KPROBE_X86_IN, 1
+
+#define __macro_err_x86 .error "ENTRY_X86/KPROBE_X86 unbalanced,missed,mixed"
+
+#define __check_entry_x86	\
+	.ifdef ENTRY_X86_IN;	\
+	.ifeq ENTRY_X86_IN;	\
+	__macro_err_x86;	\
+	.abort;			\
+	.endif;			\
+	.endif
+
+#define __check_kprobe_x86	\
+	.ifdef KPROBE_X86_IN;	\
+	.ifeq KPROBE_X86_IN;	\
+	__x86_macro_err;	\
+	.abort;			\
+	.endif;			\
+	.endif
+
+#define __check_entry_kprobe_x86	\
+	__check_entry_x86;		\
+	__check_kprobe_x86
+
+#define ENTRY_KPROBE_FINAL_X86 __check_entry_kprobe_x86
+
+#define ENTRY_X86(name)			\
+	__check_entry_kprobe_x86;	\
+	__set_entry_x86;		\
+	.globl name;			\
+	__ALIGN;			\
+	name:
+
+#define END_X86(name)			\
+	__unset_entry_x86;		\
+	__check_entry_kprobe_x86;	\
+	.size name, .-name
+
+#define KPROBE_ENTRY_X86(name)		\
+	__check_entry_kprobe_x86;	\
+	__set_kprobe_x86;		\
+	.pushsection .kprobes.text, "ax"; \
+	.globl name;			\
+	__ALIGN;			\
+	name:
+
+#define KPROBE_END_X86(name)		\
+	__unset_kprobe_x86;		\
+	__check_entry_kprobe_x86;	\
+	.size name, .-name;		\
+	.popsection
+
 #endif /* _ASM_X86_LINKAGE_H */