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1 | /* SPDX-License-Identifier: GPL-2.0 */ |
2 | #ifndef __LINUX_INSTRUMENTATION_H | |
3 | #define __LINUX_INSTRUMENTATION_H | |
4 | ||
5 | #if defined(CONFIG_DEBUG_ENTRY) && defined(CONFIG_STACK_VALIDATION) | |
6 | ||
7 | /* Begin/end of an instrumentation safe region */ | |
8 | #define instrumentation_begin() ({ \ | |
9 | asm volatile("%c0: nop\n\t" \ | |
10 | ".pushsection .discard.instr_begin\n\t" \ | |
11 | ".long %c0b - .\n\t" \ | |
12 | ".popsection\n\t" : : "i" (__COUNTER__)); \ | |
13 | }) | |
14 | ||
15 | /* | |
16 | * Because instrumentation_{begin,end}() can nest, objtool validation considers | |
17 | * _begin() a +1 and _end() a -1 and computes a sum over the instructions. | |
18 | * When the value is greater than 0, we consider instrumentation allowed. | |
19 | * | |
20 | * There is a problem with code like: | |
21 | * | |
22 | * noinstr void foo() | |
23 | * { | |
24 | * instrumentation_begin(); | |
25 | * ... | |
26 | * if (cond) { | |
27 | * instrumentation_begin(); | |
28 | * ... | |
29 | * instrumentation_end(); | |
30 | * } | |
31 | * bar(); | |
32 | * instrumentation_end(); | |
33 | * } | |
34 | * | |
35 | * If instrumentation_end() would be an empty label, like all the other | |
36 | * annotations, the inner _end(), which is at the end of a conditional block, | |
37 | * would land on the instruction after the block. | |
38 | * | |
39 | * If we then consider the sum of the !cond path, we'll see that the call to | |
40 | * bar() is with a 0-value, even though, we meant it to happen with a positive | |
41 | * value. | |
42 | * | |
43 | * To avoid this, have _end() be a NOP instruction, this ensures it will be | |
44 | * part of the condition block and does not escape. | |
45 | */ | |
46 | #define instrumentation_end() ({ \ | |
47 | asm volatile("%c0: nop\n\t" \ | |
48 | ".pushsection .discard.instr_end\n\t" \ | |
49 | ".long %c0b - .\n\t" \ | |
50 | ".popsection\n\t" : : "i" (__COUNTER__)); \ | |
51 | }) | |
52 | #else | |
53 | # define instrumentation_begin() do { } while(0) | |
54 | # define instrumentation_end() do { } while(0) | |
55 | #endif | |
56 | ||
57 | #endif /* __LINUX_INSTRUMENTATION_H */ |