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Subject[PATCH 1/3] x86/tracing: comment need for atomic nop
From: Steven Rostedt <>

The dynamic function tracer relys on the macro P6_NOP5 always being
an atomic NOP. If for some reason it is changed to be two operations
(like a nop2 nop3) it can faults within the kernel when the function
tracer modifies the code.

This patch adds a comment to note that the P6_NOPs are expected to
be atomic. This will hopefully prevent anyone from changing that.

Reported-by: Mathieu Desnoyer <>
Signed-off-by: Steven Rostedt <>
arch/x86/include/asm/nops.h | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/nops.h b/arch/x86/include/asm/nops.h
index ad2668e..6d8723a 100644
--- a/arch/x86/include/asm/nops.h
+++ b/arch/x86/include/asm/nops.h
@@ -65,6 +65,8 @@
6: osp nopl 0x00(%eax,%eax,1)
7: nopl 0x00000000(%eax)
8: nopl 0x00000000(%eax,%eax,1)
+ Note: All the above are assumed to be a single instruction.
+ There is kernel code that depends on this.
#define P6_NOP1 GENERIC_NOP1
#define P6_NOP2 ".byte 0x66,0x90\n"

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