x86/kprobes: Get rid of kretprobe_trampoline_holder()

The kretprobe_trampoline_holder() wrapper around kretprobe_trampoline()
isn't used anywhere and adds some unnecessary frame pointer instructions
which never execute.  Instead, just make kretprobe_trampoline() a proper
ELF function.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/92d921b102fb865a7c254cfde9e4a0a72b9a781e.1453405861.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/kprobes/core.c

@@ -671,38 +671,37 @@ NOKPROBE_SYMBOL(kprobe_int3_handler);
  * When a retprobed function returns, this code saves registers and
  * calls trampoline_handler() runs, which calls the kretprobe's handler.
  */
-static void __used kretprobe_trampoline_holder(void)
-{
-	asm volatile (
-			".global kretprobe_trampoline\n"
-			"kretprobe_trampoline: \n"
+asm(
+	".global kretprobe_trampoline\n"
+	".type kretprobe_trampoline, @function\n"
+	"kretprobe_trampoline:\n"
 #ifdef CONFIG_X86_64
-			/* We don't bother saving the ss register */
-			"	pushq %rsp\n"
-			"	pushfq\n"
-			SAVE_REGS_STRING
-			"	movq %rsp, %rdi\n"
-			"	call trampoline_handler\n"
-			/* Replace saved sp with true return address. */
-			"	movq %rax, 152(%rsp)\n"
-			RESTORE_REGS_STRING
-			"	popfq\n"
+	/* We don't bother saving the ss register */
+	"	pushq %rsp\n"
+	"	pushfq\n"
+	SAVE_REGS_STRING
+	"	movq %rsp, %rdi\n"
+	"	call trampoline_handler\n"
+	/* Replace saved sp with true return address. */
+	"	movq %rax, 152(%rsp)\n"
+	RESTORE_REGS_STRING
+	"	popfq\n"
 #else
-			"	pushf\n"
-			SAVE_REGS_STRING
-			"	movl %esp, %eax\n"
-			"	call trampoline_handler\n"
-			/* Move flags to cs */
-			"	movl 56(%esp), %edx\n"
-			"	movl %edx, 52(%esp)\n"
-			/* Replace saved flags with true return address. */
-			"	movl %eax, 56(%esp)\n"
-			RESTORE_REGS_STRING
-			"	popf\n"
+	"	pushf\n"
+	SAVE_REGS_STRING
+	"	movl %esp, %eax\n"
+	"	call trampoline_handler\n"
+	/* Move flags to cs */
+	"	movl 56(%esp), %edx\n"
+	"	movl %edx, 52(%esp)\n"
+	/* Replace saved flags with true return address. */
+	"	movl %eax, 56(%esp)\n"
+	RESTORE_REGS_STRING
+	"	popf\n"
 #endif
-			"	ret\n");
-}
-NOKPROBE_SYMBOL(kretprobe_trampoline_holder);
+	"	ret\n"
+	".size kretprobe_trampoline, .-kretprobe_trampoline\n"
+);
 NOKPROBE_SYMBOL(kretprobe_trampoline);
 
 /*