instrumentation.h

 1/* SPDX-License-Identifier: GPL-2.0 */
 2#ifndef __LINUX_INSTRUMENTATION_H
 3#define __LINUX_INSTRUMENTATION_H
 4
 5#ifdef CONFIG_NOINSTR_VALIDATION
 6
 7#include <linux/objtool.h>
 8#include <linux/stringify.h>
 9
10/* Begin/end of an instrumentation safe region */
11#define __instrumentation_begin(c) ({					\
12	asm volatile(__stringify(c) ": nop\n\t"				\
13		     ANNOTATE_INSTR_BEGIN(__ASM_BREF(c))		\
14		     : : "i" (c));					\
15})
16#define instrumentation_begin() __instrumentation_begin(__COUNTER__)
17
18/*
19 * Because instrumentation_{begin,end}() can nest, objtool validation considers
20 * _begin() a +1 and _end() a -1 and computes a sum over the instructions.
21 * When the value is greater than 0, we consider instrumentation allowed.
22 *
23 * There is a problem with code like:
24 *
25 * noinstr void foo()
26 * {
27 *	instrumentation_begin();
28 *	...
29 *	if (cond) {
30 *		instrumentation_begin();
31 *		...
32 *		instrumentation_end();
33 *	}
34 *	bar();
35 *	instrumentation_end();
36 * }
37 *
38 * If instrumentation_end() would be an empty label, like all the other
39 * annotations, the inner _end(), which is at the end of a conditional block,
40 * would land on the instruction after the block.
41 *
42 * If we then consider the sum of the !cond path, we'll see that the call to
43 * bar() is with a 0-value, even though, we meant it to happen with a positive
44 * value.
45 *
46 * To avoid this, have _end() be a NOP instruction, this ensures it will be
47 * part of the condition block and does not escape.
48 */
49#define __instrumentation_end(c) ({					\
50	asm volatile(__stringify(c) ": nop\n\t"				\
51		     ANNOTATE_INSTR_END(__ASM_BREF(c))			\
52		     : : "i" (c));					\
53})
54#define instrumentation_end() __instrumentation_end(__COUNTER__)
55#else /* !CONFIG_NOINSTR_VALIDATION */
56# define instrumentation_begin()	do { } while(0)
57# define instrumentation_end()		do { } while(0)
58#endif /* CONFIG_NOINSTR_VALIDATION */
59
60#endif /* __LINUX_INSTRUMENTATION_H */