name : instrumentation.h /* SPDX-License-Identifier: GPL-2.0 */ #ifndef __LINUX_INSTRUMENTATION_H #define __LINUX_INSTRUMENTATION_H #ifdef CONFIG_NOINSTR_VALIDATION #include <linux/stringify.h> /* Begin/end of an instrumentation safe region */ #define __instrumentation_begin(c) ({ \ asm volatile(__stringify(c) ": nop\n\t" \ ".pushsection .discard.instr_begin\n\t" \ ".long " __stringify(c) "b - .\n\t" \ ".popsection\n\t" : : "i" (c)); \ }) #define instrumentation_begin() __instrumentation_begin(__COUNTER__) /* * Because instrumentation_{begin,end}() can nest, objtool validation considers * _begin() a +1 and _end() a -1 and computes a sum over the instructions. * When the value is greater than 0, we consider instrumentation allowed. * * There is a problem with code like: * * noinstr void foo() * { * instrumentation_begin(); * ... * if (cond) { * instrumentation_begin(); * ... * instrumentation_end(); * } * bar(); * instrumentation_end(); * } * * If instrumentation_end() would be an empty label, like all the other * annotations, the inner _end(), which is at the end of a conditional block, * would land on the instruction after the block. * * If we then consider the sum of the !cond path, we'll see that the call to * bar() is with a 0-value, even though, we meant it to happen with a positive * value. * * To avoid this, have _end() be a NOP instruction, this ensures it will be * part of the condition block and does not escape. */ #define __instrumentation_end(c) ({ \ asm volatile(__stringify(c) ": nop\n\t" \ ".pushsection .discard.instr_end\n\t" \ ".long " __stringify(c) "b - .\n\t" \ ".popsection\n\t" : : "i" (c)); \ }) #define instrumentation_end() __instrumentation_end(__COUNTER__) #else /* !CONFIG_NOINSTR_VALIDATION */ # define instrumentation_begin() do { } while(0) # define instrumentation_end() do { } while(0) #endif /* CONFIG_NOINSTR_VALIDATION */ #endif /* __LINUX_INSTRUMENTATION_H */