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 */
61