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x86/tracing: comment need for atomic nop

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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 <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2009-09-10 17:22:44 -04:00 committed by Steven Rostedt
parent 197e2eabc9
commit fc06b8520b
1 changed files with 2 additions and 0 deletions
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2
arch/x86/include/asm/nops.h
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@ -65,6 +65,8 @@
6: osp nopl 0x00(%eax,%eax,1) 6: osp nopl 0x00(%eax,%eax,1)
7: nopl 0x00000000(%eax) 7: nopl 0x00000000(%eax)
8: nopl 0x00000000(%eax,%eax,1) 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_NOP1 GENERIC_NOP1
#define P6_NOP2 ".byte 0x66,0x90\n" #define P6_NOP2 ".byte 0x66,0x90\n"