[linux-2.6-block.git] / include / linux / 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 */
Commit	Line	Data
d19e789f IM	1	/* SPDX-License-Identifier: GPL-2.0 */
	2	#ifndef __LINUX_INSTRUMENTATION_H
	3	#define __LINUX_INSTRUMENTATION_H
	4
0f620cef	5	#ifdef CONFIG_NOINSTR_VALIDATION
d19e789f	6
c199f64f VG	7	#include <linux/stringify.h>
c199f64f VG	8
d19e789f	9	/* Begin/end of an instrumentation safe region */
c199f64f VG	10	#define __instrumentation_begin(c) ({ \
c199f64f VG	11	asm volatile(__stringify(c) ": nop\n\t" \
d19e789f	12	".pushsection .discard.instr_begin\n\t" \
c199f64f	13	".long " __stringify(c) "b - .\n\t" \
dcce50e6	14	".popsection\n\t" : : "i" (c)); \
d19e789f	15	})
c199f64f	16	#define instrumentation_begin() __instrumentation_begin(__COUNTER__)
d19e789f IM	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	*/
c199f64f VG	49	#define __instrumentation_end(c) ({ \
c199f64f VG	50	asm volatile(__stringify(c) ": nop\n\t" \
d19e789f	51	".pushsection .discard.instr_end\n\t" \
c199f64f	52	".long " __stringify(c) "b - .\n\t" \
dcce50e6	53	".popsection\n\t" : : "i" (c)); \
d19e789f	54	})
c199f64f	55	#define instrumentation_end() __instrumentation_end(__COUNTER__)
0f620cef	56	#else /* !CONFIG_NOINSTR_VALIDATION */
d19e789f IM	57	# define instrumentation_begin() do { } while(0)
d19e789f IM	58	# define instrumentation_end() do { } while(0)
0f620cef	59	#endif /* CONFIG_NOINSTR_VALIDATION */
d19e789f IM	60
d19e789f IM	61	#endif /* __LINUX_INSTRUMENTATION_H */