linux-kernel - [tip:x86/debug] x86/kprobes: Get rid of kretprobe_trampoline

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Date:	Wed, 24 Feb 2016 21:51:31 -0800
From:	tip-bot for Josh Poimboeuf <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	peterz@...radead.org, torvalds@...ux-foundation.org,
	luto@...capital.net, masami.hiramatsu.pt@...achi.com, bp@...en8.de,
	anil.s.keshavamurthy@...el.com, mingo@...nel.org,
	palves@...hat.com, linux-kernel@...r.kernel.org, mmarek@...e.cz,
	dvlasenk@...hat.com, bernd@...rovitsch.priv.at, jslaby@...e.cz,
	chris.j.arges@...onical.com, davem@...emloft.net,
	akpm@...ux-foundation.org, acme@...nel.org, brgerst@...il.com,
	luto@...nel.org, hpa@...or.com, ananth@...ibm.com,
	jpoimboe@...hat.com, namhyung@...il.com, tglx@...utronix.de
Subject: [tip:x86/debug] x86/kprobes: Get rid of
 kretprobe_trampoline_holder()

Commit-ID:  c1c355ce14c037666fbcb9453d9067c86bbdda5c
Gitweb:     http://git.kernel.org/tip/c1c355ce14c037666fbcb9453d9067c86bbdda5c
Author:     Josh Poimboeuf <jpoimboe@...hat.com>
AuthorDate: Thu, 21 Jan 2016 16:49:28 -0600
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 24 Feb 2016 08:35:44 +0100

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@...hat.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Bernd Petrovitsch <bernd@...rovitsch.priv.at>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: Chris J Arges <chris.j.arges@...onical.com>
Cc: David S. Miller <davem@...emloft.net>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Jiri Slaby <jslaby@...e.cz>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Michal Marek <mmarek@...e.cz>
Cc: Namhyung Kim <namhyung@...il.com>
Cc: Pedro Alves <palves@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: live-patching@...r.kernel.org
Link: http://lkml.kernel.org/r/92d921b102fb865a7c254cfde9e4a0a72b9a781e.1453405861.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/kprobes/core.c | 57 +++++++++++++++++++++---------------------
 1 file changed, 28 insertions(+), 29 deletions(-)

diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 1deffe6..5b187df 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/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);
 
 /*