| Olivier Deprez | 157378f | 2022-04-04 15:47:50 +0200 | [diff] [blame] | 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 */ |