swh:1:snp:c3bf2749e3476071fa748f67b0ffa2fdc5fe49d9
Tip revision: 3123109284176b1532874591f7c81f3837bbdc17 authored by Linus Torvalds on 03 April 2022, 21:08:21 UTC
Linux 5.18-rc1
Linux 5.18-rc1
Tip revision: 3123109
instrumentation.h
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __LINUX_INSTRUMENTATION_H
#define __LINUX_INSTRUMENTATION_H
#if defined(CONFIG_DEBUG_ENTRY) && defined(CONFIG_STACK_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
# define instrumentation_begin() do { } while(0)
# define instrumentation_end() do { } while(0)
#endif
#endif /* __LINUX_INSTRUMENTATION_H */