linux-kernel - [PATCH] ftrace: Make ftrace_test

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Date:	Thu, 9 Oct 2008 22:19:08 -0400 (EDT)
From:	Anders Kaseorg <andersk@....EDU>
To:	Ingo Molnar <mingo@...e.hu>
cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org
Subject: [PATCH] ftrace: Make ftrace_test_p6nop disassembler-friendly

Commit 4c3dc21b136f8cb4b72afee16c3ba7e961656c0b in tip introduced the
5-byte NOP ftrace_test_p6nop:
  jmp . + 5
  .byte 0x00, 0x00, 0x00
This is not friendly to disassemblers because an odd number of 0x00s
ends in the middle of an instruction boundary.  This changes the 0x00s
to 1-byte NOPs (0x90).

Signed-off-by: Anders Kaseorg <andersk@....edu>

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 222507e..d073d98 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -132,7 +132,9 @@ int __init ftrace_dyn_arch_init(void *data)
 		".section .text, \"ax\"\n"
 		"ftrace_test_jmp:"
 		"jmp ftrace_test_p6nop\n"
-		".byte 0x00,0x00,0x00\n"  /* 2 byte jmp + 3 bytes */
+		"nop\n"
+		"nop\n"
+		"nop\n"  /* 2 byte jmp + 3 bytes */
 		"ftrace_test_p6nop:"
 		P6_NOP5
 		"jmp 1f\n"
@@ -161,7 +163,7 @@ int __init ftrace_dyn_arch_init(void *data)
 		ftrace_nop = (unsigned long *)ftrace_test_nop5;
 		break;
 	case 2:
-		pr_info("ftrace: converting mcount calls to jmp 1f\n");
+		pr_info("ftrace: converting mcount calls to jmp . + 5\n");
 		ftrace_nop = (unsigned long *)ftrace_test_jmp;
 		break;
 	}
--
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