* [PATCH] ftrace: Make ftrace_test_p6nop disassembler-friendly
@ 2008-10-10 2:19 Anders Kaseorg
2008-10-10 8:54 ` Ingo Molnar
0 siblings, 1 reply; 5+ messages in thread
From: Anders Kaseorg @ 2008-10-10 2:19 UTC (permalink / raw)
To: Ingo Molnar; +Cc: Steven Rostedt, linux-kernel
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@mit.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;
}
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] ftrace: Make ftrace_test_p6nop disassembler-friendly
2008-10-10 2:19 [PATCH] ftrace: Make ftrace_test_p6nop disassembler-friendly Anders Kaseorg
@ 2008-10-10 8:54 ` Ingo Molnar
2008-10-10 13:27 ` Steven Rostedt
0 siblings, 1 reply; 5+ messages in thread
From: Ingo Molnar @ 2008-10-10 8:54 UTC (permalink / raw)
To: Anders Kaseorg; +Cc: Steven Rostedt, linux-kernel, H. Peter Anvin
* Anders Kaseorg <andersk@MIT.EDU> wrote:
> 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@mit.edu>
applied to tip/tracing/ftrace, good spotting Anders!
Steve, any objections?
Ingo
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] ftrace: Make ftrace_test_p6nop disassembler-friendly
2008-10-10 8:54 ` Ingo Molnar
@ 2008-10-10 13:27 ` Steven Rostedt
2008-10-10 16:12 ` H. Peter Anvin
0 siblings, 1 reply; 5+ messages in thread
From: Steven Rostedt @ 2008-10-10 13:27 UTC (permalink / raw)
To: Ingo Molnar; +Cc: Anders Kaseorg, linux-kernel, H. Peter Anvin
On Fri, 10 Oct 2008, Ingo Molnar wrote:
>
> * Anders Kaseorg <andersk@MIT.EDU> wrote:
>
> > 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@mit.edu>
>
> applied to tip/tracing/ftrace, good spotting Anders!
>
> Steve, any objections?
Nope, it's fine with me.
Acked-by: Steven Rostedt <srostedt@redhat.com>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] ftrace: Make ftrace_test_p6nop disassembler-friendly
2008-10-10 13:27 ` Steven Rostedt
@ 2008-10-10 16:12 ` H. Peter Anvin
2008-10-10 16:56 ` Steven Rostedt
0 siblings, 1 reply; 5+ messages in thread
From: H. Peter Anvin @ 2008-10-10 16:12 UTC (permalink / raw)
To: Steven Rostedt; +Cc: Ingo Molnar, Anders Kaseorg, linux-kernel
Steven Rostedt wrote:
> On Fri, 10 Oct 2008, Ingo Molnar wrote:
>
>> * Anders Kaseorg <andersk@MIT.EDU> wrote:
>>
>>> 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@mit.edu>
>> applied to tip/tracing/ftrace, good spotting Anders!
>>
>> Steve, any objections?
>
> Nope, it's fine with me.
>
> Acked-by: Steven Rostedt <srostedt@redhat.com>
>
The (semi-)amusing thing is that it should never, ever, get there.
66 66 66 66 90 is used over this, which should always work.
-hpa
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] ftrace: Make ftrace_test_p6nop disassembler-friendly
2008-10-10 16:12 ` H. Peter Anvin
@ 2008-10-10 16:56 ` Steven Rostedt
0 siblings, 0 replies; 5+ messages in thread
From: Steven Rostedt @ 2008-10-10 16:56 UTC (permalink / raw)
To: H. Peter Anvin; +Cc: Ingo Molnar, Anders Kaseorg, linux-kernel
On Fri, 10 Oct 2008, H. Peter Anvin wrote:
>
> The (semi-)amusing thing is that it should never, ever, get there.
> 66 66 66 66 90 is used over this, which should always work.
Yeah, that was me being overly paranoid ;-) Which is not always a bad
thing.
-- Steve
^ permalink raw reply [flat|nested] 5+ messages in thread
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2008-10-10 2:19 [PATCH] ftrace: Make ftrace_test_p6nop disassembler-friendly Anders Kaseorg
2008-10-10 8:54 ` Ingo Molnar
2008-10-10 13:27 ` Steven Rostedt
2008-10-10 16:12 ` H. Peter Anvin
2008-10-10 16:56 ` Steven Rostedt
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