tools/lib/bpf/bpf_core_read.h - linux/kernel/git/bpf/bpf - Git at Google

 /* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
 #ifndef __BPF_CORE_READ_H__
 #define __BPF_CORE_READ_H__

 /*
  * enum bpf_field_info_kind is passed as a second argument into
  * __builtin_preserve_field_info() built-in to get a specific aspect of
  * a field, captured as a first argument. __builtin_preserve_field_info(field,
  * info_kind) returns __u32 integer and produces BTF field relocation, which
  * is understood and processed by libbpf during BPF object loading. See
  * selftests/bpf for examples.
  */
 enum bpf_field_info_kind {
 	BPF_FIELD_BYTE_OFFSET = 0,	/* field byte offset */
 	BPF_FIELD_BYTE_SIZE = 1,
 	BPF_FIELD_EXISTS = 2,		/* field existence in target kernel */
 	BPF_FIELD_SIGNED = 3,
 	BPF_FIELD_LSHIFT_U64 = 4,
 	BPF_FIELD_RSHIFT_U64 = 5,
 };

 #define __CORE_RELO(src, field, info)					      \
 	__builtin_preserve_field_info((src)->field, BPF_FIELD_##info)

 #if __BYTE_ORDER == __LITTLE_ENDIAN
 #define __CORE_BITFIELD_PROBE_READ(dst, src, fld)			      \
 	bpf_probe_read((void *)dst,					      \
 		       __CORE_RELO(src, fld, BYTE_SIZE),		      \
 		       (const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
 #else
 /* semantics of LSHIFT_64 assumes loading values into low-ordered bytes, so
  * for big-endian we need to adjust destination pointer accordingly, based on
  * field byte size
  */
 #define __CORE_BITFIELD_PROBE_READ(dst, src, fld)			      \
 	bpf_probe_read((void *)dst + (8 - __CORE_RELO(src, fld, BYTE_SIZE)),  \
 		       __CORE_RELO(src, fld, BYTE_SIZE),		      \
 		       (const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
 #endif

 /*
  * Extract bitfield, identified by s->field, and return its value as u64.
  * All this is done in relocatable manner, so bitfield changes such as
  * signedness, bit size, offset changes, this will be handled automatically.
  * This version of macro is using bpf_probe_read() to read underlying integer
  * storage. Macro functions as an expression and its return type is
  * bpf_probe_read()'s return value: 0, on success, <0 on error.
  */
 #define BPF_CORE_READ_BITFIELD_PROBED(s, field) ({			      \
 	unsigned long long val = 0;					      \
 									      \
 	__CORE_BITFIELD_PROBE_READ(&val, s, field);			      \
 	val <<= __CORE_RELO(s, field, LSHIFT_U64);			      \
 	if (__CORE_RELO(s, field, SIGNED))				      \
 		val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64);  \
 	else								      \
 		val = val >> __CORE_RELO(s, field, RSHIFT_U64);		      \
 	val;								      \
 })

 /*
  * Extract bitfield, identified by s->field, and return its value as u64.
  * This version of macro is using direct memory reads and should be used from
  * BPF program types that support such functionality (e.g., typed raw
  * tracepoints).
  */
 #define BPF_CORE_READ_BITFIELD(s, field) ({				      \
 	const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
 	unsigned long long val;						      \
 									      \
 	switch (__CORE_RELO(s, field, BYTE_SIZE)) {			      \
 	case 1: val = *(const unsigned char *)p;			      \
 	case 2: val = *(const unsigned short *)p;			      \
 	case 4: val = *(const unsigned int *)p;				      \
 	case 8: val = *(const unsigned long long *)p;			      \
 	}								      \
 	val <<= __CORE_RELO(s, field, LSHIFT_U64);			      \
 	if (__CORE_RELO(s, field, SIGNED))				      \
 		val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64);  \
 	else								      \
 		val = val >> __CORE_RELO(s, field, RSHIFT_U64);		      \
 	val;								      \
 })

 /*
  * Convenience macro to check that field actually exists in target kernel's.
  * Returns:
  *    1, if matching field is present in target kernel;
  *    0, if no matching field found.
  */
 #define bpf_core_field_exists(field)					    \
 	__builtin_preserve_field_info(field, BPF_FIELD_EXISTS)

 /*
  * Convenience macro to get byte size of a field. Works for integers,
  * struct/unions, pointers, arrays, and enums.
  */
 #define bpf_core_field_size(field)					    \
 	__builtin_preserve_field_info(field, BPF_FIELD_BYTE_SIZE)

 /*
  * bpf_core_read() abstracts away bpf_probe_read() call and captures offset
  * relocation for source address using __builtin_preserve_access_index()
  * built-in, provided by Clang.
  *
  * __builtin_preserve_access_index() takes as an argument an expression of
  * taking an address of a field within struct/union. It makes compiler emit
  * a relocation, which records BTF type ID describing root struct/union and an
  * accessor string which describes exact embedded field that was used to take
  * an address. See detailed description of this relocation format and
  * semantics in comments to struct bpf_field_reloc in libbpf_internal.h.
  *
  * This relocation allows libbpf to adjust BPF instruction to use correct
  * actual field offset, based on target kernel BTF type that matches original
  * (local) BTF, used to record relocation.
  */
 #define bpf_core_read(dst, sz, src)					    \
 	bpf_probe_read(dst, sz,						    \
 		       (const void *)__builtin_preserve_access_index(src))

 /*
  * bpf_core_read_str() is a thin wrapper around bpf_probe_read_str()
  * additionally emitting BPF CO-RE field relocation for specified source
  * argument.
  */
 #define bpf_core_read_str(dst, sz, src)					    \
 	bpf_probe_read_str(dst, sz,					    \
 			   (const void *)__builtin_preserve_access_index(src))

 #define ___concat(a, b) a ## b
 #define ___apply(fn, n) ___concat(fn, n)
 #define ___nth(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, __11, N, ...) N

 /*
  * return number of provided arguments; used for switch-based variadic macro
  * definitions (see ___last, ___arrow, etc below)
  */
 #define ___narg(...) ___nth(_, ##__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
 /*
  * return 0 if no arguments are passed, N - otherwise; used for
  * recursively-defined macros to specify termination (0) case, and generic
  * (N) case (e.g., ___read_ptrs, ___core_read)
  */
 #define ___empty(...) ___nth(_, ##__VA_ARGS__, N, N, N, N, N, N, N, N, N, N, 0)

 #define ___last1(x) x
 #define ___last2(a, x) x
 #define ___last3(a, b, x) x
 #define ___last4(a, b, c, x) x
 #define ___last5(a, b, c, d, x) x
 #define ___last6(a, b, c, d, e, x) x
 #define ___last7(a, b, c, d, e, f, x) x
 #define ___last8(a, b, c, d, e, f, g, x) x
 #define ___last9(a, b, c, d, e, f, g, h, x) x
 #define ___last10(a, b, c, d, e, f, g, h, i, x) x
 #define ___last(...) ___apply(___last, ___narg(__VA_ARGS__))(__VA_ARGS__)

 #define ___nolast2(a, _) a
 #define ___nolast3(a, b, _) a, b
 #define ___nolast4(a, b, c, _) a, b, c
 #define ___nolast5(a, b, c, d, _) a, b, c, d
 #define ___nolast6(a, b, c, d, e, _) a, b, c, d, e
 #define ___nolast7(a, b, c, d, e, f, _) a, b, c, d, e, f
 #define ___nolast8(a, b, c, d, e, f, g, _) a, b, c, d, e, f, g
 #define ___nolast9(a, b, c, d, e, f, g, h, _) a, b, c, d, e, f, g, h
 #define ___nolast10(a, b, c, d, e, f, g, h, i, _) a, b, c, d, e, f, g, h, i
 #define ___nolast(...) ___apply(___nolast, ___narg(__VA_ARGS__))(__VA_ARGS__)

 #define ___arrow1(a) a
 #define ___arrow2(a, b) a->b
 #define ___arrow3(a, b, c) a->b->c
 #define ___arrow4(a, b, c, d) a->b->c->d
 #define ___arrow5(a, b, c, d, e) a->b->c->d->e
 #define ___arrow6(a, b, c, d, e, f) a->b->c->d->e->f
 #define ___arrow7(a, b, c, d, e, f, g) a->b->c->d->e->f->g
 #define ___arrow8(a, b, c, d, e, f, g, h) a->b->c->d->e->f->g->h
 #define ___arrow9(a, b, c, d, e, f, g, h, i) a->b->c->d->e->f->g->h->i
 #define ___arrow10(a, b, c, d, e, f, g, h, i, j) a->b->c->d->e->f->g->h->i->j
 #define ___arrow(...) ___apply(___arrow, ___narg(__VA_ARGS__))(__VA_ARGS__)

 #define ___type(...) typeof(___arrow(__VA_ARGS__))

 #define ___read(read_fn, dst, src_type, src, accessor)			    \
 	read_fn((void *)(dst), sizeof(*(dst)), &((src_type)(src))->accessor)

 /* "recursively" read a sequence of inner pointers using local __t var */
 #define ___rd_first(src, a) ___read(bpf_core_read, &__t, ___type(src), src, a);
 #define ___rd_last(...)							    \
 	___read(bpf_core_read, &__t,					    \
 		___type(___nolast(__VA_ARGS__)), __t, ___last(__VA_ARGS__));
 #define ___rd_p1(...) const void *__t; ___rd_first(__VA_ARGS__)
 #define ___rd_p2(...) ___rd_p1(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 #define ___rd_p3(...) ___rd_p2(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 #define ___rd_p4(...) ___rd_p3(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 #define ___rd_p5(...) ___rd_p4(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 #define ___rd_p6(...) ___rd_p5(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 #define ___rd_p7(...) ___rd_p6(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 #define ___rd_p8(...) ___rd_p7(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 #define ___rd_p9(...) ___rd_p8(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
 #define ___read_ptrs(src, ...)						    \
 	___apply(___rd_p, ___narg(__VA_ARGS__))(src, __VA_ARGS__)

 #define ___core_read0(fn, dst, src, a)					    \
 	___read(fn, dst, ___type(src), src, a);
 #define ___core_readN(fn, dst, src, ...)				    \
 	___read_ptrs(src, ___nolast(__VA_ARGS__))			    \
 	___read(fn, dst, ___type(src, ___nolast(__VA_ARGS__)), __t,	    \
 		___last(__VA_ARGS__));
 #define ___core_read(fn, dst, src, a, ...)				    \
 	___apply(___core_read, ___empty(__VA_ARGS__))(fn, dst,		    \
 						      src, a, ##__VA_ARGS__)

 /*
  * BPF_CORE_READ_INTO() is a more performance-conscious variant of
  * BPF_CORE_READ(), in which final field is read into user-provided storage.
  * See BPF_CORE_READ() below for more details on general usage.
  */
 #define BPF_CORE_READ_INTO(dst, src, a, ...)				    \
 	({								    \
 		___core_read(bpf_core_read, dst, src, a, ##__VA_ARGS__)	    \
 	})

 /*
  * BPF_CORE_READ_STR_INTO() does same "pointer chasing" as
  * BPF_CORE_READ() for intermediate pointers, but then executes (and returns
  * corresponding error code) bpf_core_read_str() for final string read.
  */
 #define BPF_CORE_READ_STR_INTO(dst, src, a, ...)			    \
 	({								    \
 		___core_read(bpf_core_read_str, dst, src, a, ##__VA_ARGS__) \
 	})

 /*
  * BPF_CORE_READ() is used to simplify BPF CO-RE relocatable read, especially
  * when there are few pointer chasing steps.
  * E.g., what in non-BPF world (or in BPF w/ BCC) would be something like:
  *	int x = s->a.b.c->d.e->f->g;
  * can be succinctly achieved using BPF_CORE_READ as:
  *	int x = BPF_CORE_READ(s, a.b.c, d.e, f, g);
  *
  * BPF_CORE_READ will decompose above statement into 4 bpf_core_read (BPF
  * CO-RE relocatable bpf_probe_read() wrapper) calls, logically equivalent to:
  * 1. const void *__t = s->a.b.c;
  * 2. __t = __t->d.e;
  * 3. __t = __t->f;
  * 4. return __t->g;
  *
  * Equivalence is logical, because there is a heavy type casting/preservation
  * involved, as well as all the reads are happening through bpf_probe_read()
  * calls using __builtin_preserve_access_index() to emit CO-RE relocations.
  *
  * N.B. Only up to 9 "field accessors" are supported, which should be more
  * than enough for any practical purpose.
  */
 #define BPF_CORE_READ(src, a, ...)					    \
 	({								    \
 		___type(src, a, ##__VA_ARGS__) __r;			    \
 		BPF_CORE_READ_INTO(&__r, src, a, ##__VA_ARGS__);	    \
 		__r;							    \
 	})

 #endif
	/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
	#ifndef __BPF_CORE_READ_H__
	#define __BPF_CORE_READ_H__

	/*
	* enum bpf_field_info_kind is passed as a second argument into
	* __builtin_preserve_field_info() built-in to get a specific aspect of
	* a field, captured as a first argument. __builtin_preserve_field_info(field,
	* info_kind) returns __u32 integer and produces BTF field relocation, which
	* is understood and processed by libbpf during BPF object loading. See
	* selftests/bpf for examples.
	*/
	enum bpf_field_info_kind {
	BPF_FIELD_BYTE_OFFSET = 0, /* field byte offset */
	BPF_FIELD_BYTE_SIZE = 1,
	BPF_FIELD_EXISTS = 2, /* field existence in target kernel */
	BPF_FIELD_SIGNED = 3,
	BPF_FIELD_LSHIFT_U64 = 4,
	BPF_FIELD_RSHIFT_U64 = 5,
	};

	#define __CORE_RELO(src, field, info) \
	__builtin_preserve_field_info((src)->field, BPF_FIELD_##info)

	#if __BYTE_ORDER == __LITTLE_ENDIAN
	#define __CORE_BITFIELD_PROBE_READ(dst, src, fld) \
	bpf_probe_read((void *)dst, \
	__CORE_RELO(src, fld, BYTE_SIZE), \
	(const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
	#else
	/* semantics of LSHIFT_64 assumes loading values into low-ordered bytes, so
	* for big-endian we need to adjust destination pointer accordingly, based on
	* field byte size
	*/
	#define __CORE_BITFIELD_PROBE_READ(dst, src, fld) \
	bpf_probe_read((void *)dst + (8 - __CORE_RELO(src, fld, BYTE_SIZE)), \
	__CORE_RELO(src, fld, BYTE_SIZE), \
	(const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
	#endif

	/*
	* Extract bitfield, identified by s->field, and return its value as u64.
	* All this is done in relocatable manner, so bitfield changes such as
	* signedness, bit size, offset changes, this will be handled automatically.
	* This version of macro is using bpf_probe_read() to read underlying integer
	* storage. Macro functions as an expression and its return type is
	* bpf_probe_read()'s return value: 0, on success, <0 on error.
	*/
	#define BPF_CORE_READ_BITFIELD_PROBED(s, field) ({ \
	unsigned long long val = 0; \
	\
	__CORE_BITFIELD_PROBE_READ(&val, s, field); \
	val <<= __CORE_RELO(s, field, LSHIFT_U64); \
	if (__CORE_RELO(s, field, SIGNED)) \
	val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64); \
	else \
	val = val >> __CORE_RELO(s, field, RSHIFT_U64); \
	val; \
	})

	/*
	* Extract bitfield, identified by s->field, and return its value as u64.
	* This version of macro is using direct memory reads and should be used from
	* BPF program types that support such functionality (e.g., typed raw
	* tracepoints).
	*/
	#define BPF_CORE_READ_BITFIELD(s, field) ({ \
	const void p = (const void )s + __CORE_RELO(s, field, BYTE_OFFSET); \
	unsigned long long val; \
	\
	switch (__CORE_RELO(s, field, BYTE_SIZE)) { \
	case 1: val = (const unsigned char )p; \
	case 2: val = (const unsigned short )p; \
	case 4: val = (const unsigned int )p; \
	case 8: val = (const unsigned long long )p; \
	} \
	val <<= __CORE_RELO(s, field, LSHIFT_U64); \
	if (__CORE_RELO(s, field, SIGNED)) \
	val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64); \
	else \
	val = val >> __CORE_RELO(s, field, RSHIFT_U64); \
	val; \
	})

	/*
	* Convenience macro to check that field actually exists in target kernel's.
	* Returns:
	* 1, if matching field is present in target kernel;
	* 0, if no matching field found.
	*/
	#define bpf_core_field_exists(field) \
	__builtin_preserve_field_info(field, BPF_FIELD_EXISTS)

	/*
	* Convenience macro to get byte size of a field. Works for integers,
	* struct/unions, pointers, arrays, and enums.
	*/
	#define bpf_core_field_size(field) \
	__builtin_preserve_field_info(field, BPF_FIELD_BYTE_SIZE)

	/*
	* bpf_core_read() abstracts away bpf_probe_read() call and captures offset
	* relocation for source address using __builtin_preserve_access_index()
	* built-in, provided by Clang.
	*
	* __builtin_preserve_access_index() takes as an argument an expression of
	* taking an address of a field within struct/union. It makes compiler emit
	* a relocation, which records BTF type ID describing root struct/union and an
	* accessor string which describes exact embedded field that was used to take
	* an address. See detailed description of this relocation format and
	* semantics in comments to struct bpf_field_reloc in libbpf_internal.h.
	*
	* This relocation allows libbpf to adjust BPF instruction to use correct
	* actual field offset, based on target kernel BTF type that matches original
	* (local) BTF, used to record relocation.
	*/
	#define bpf_core_read(dst, sz, src) \
	bpf_probe_read(dst, sz, \
	(const void *)__builtin_preserve_access_index(src))

	/*
	* bpf_core_read_str() is a thin wrapper around bpf_probe_read_str()
	* additionally emitting BPF CO-RE field relocation for specified source
	* argument.
	*/
	#define bpf_core_read_str(dst, sz, src) \
	bpf_probe_read_str(dst, sz, \
	(const void *)__builtin_preserve_access_index(src))

	#define ___concat(a, b) a ## b
	#define ___apply(fn, n) ___concat(fn, n)
	#define ___nth(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, __11, N, ...) N

	/*
	* return number of provided arguments; used for switch-based variadic macro
	* definitions (see ___last, ___arrow, etc below)
	*/
	#define ___narg(...) ___nth(_, ##__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
	/*
	* return 0 if no arguments are passed, N - otherwise; used for
	* recursively-defined macros to specify termination (0) case, and generic
	* (N) case (e.g., ___read_ptrs, ___core_read)
	*/
	#define ___empty(...) ___nth(_, ##__VA_ARGS__, N, N, N, N, N, N, N, N, N, N, 0)

	#define ___last1(x) x
	#define ___last2(a, x) x
	#define ___last3(a, b, x) x
	#define ___last4(a, b, c, x) x
	#define ___last5(a, b, c, d, x) x
	#define ___last6(a, b, c, d, e, x) x
	#define ___last7(a, b, c, d, e, f, x) x
	#define ___last8(a, b, c, d, e, f, g, x) x
	#define ___last9(a, b, c, d, e, f, g, h, x) x
	#define ___last10(a, b, c, d, e, f, g, h, i, x) x
	#define ___last(...) ___apply(___last, ___narg(__VA_ARGS__))(__VA_ARGS__)

	#define ___nolast2(a, _) a
	#define ___nolast3(a, b, _) a, b
	#define ___nolast4(a, b, c, _) a, b, c
	#define ___nolast5(a, b, c, d, _) a, b, c, d
	#define ___nolast6(a, b, c, d, e, _) a, b, c, d, e
	#define ___nolast7(a, b, c, d, e, f, _) a, b, c, d, e, f
	#define ___nolast8(a, b, c, d, e, f, g, _) a, b, c, d, e, f, g
	#define ___nolast9(a, b, c, d, e, f, g, h, _) a, b, c, d, e, f, g, h
	#define ___nolast10(a, b, c, d, e, f, g, h, i, _) a, b, c, d, e, f, g, h, i
	#define ___nolast(...) ___apply(___nolast, ___narg(__VA_ARGS__))(__VA_ARGS__)

	#define ___arrow1(a) a
	#define ___arrow2(a, b) a->b
	#define ___arrow3(a, b, c) a->b->c
	#define ___arrow4(a, b, c, d) a->b->c->d
	#define ___arrow5(a, b, c, d, e) a->b->c->d->e
	#define ___arrow6(a, b, c, d, e, f) a->b->c->d->e->f
	#define ___arrow7(a, b, c, d, e, f, g) a->b->c->d->e->f->g
	#define ___arrow8(a, b, c, d, e, f, g, h) a->b->c->d->e->f->g->h
	#define ___arrow9(a, b, c, d, e, f, g, h, i) a->b->c->d->e->f->g->h->i
	#define ___arrow10(a, b, c, d, e, f, g, h, i, j) a->b->c->d->e->f->g->h->i->j
	#define ___arrow(...) ___apply(___arrow, ___narg(__VA_ARGS__))(__VA_ARGS__)

	#define ___type(...) typeof(___arrow(__VA_ARGS__))

	#define ___read(read_fn, dst, src_type, src, accessor) \
	read_fn((void )(dst), sizeof((dst)), &((src_type)(src))->accessor)

	/* "recursively" read a sequence of inner pointers using local __t var */
	#define ___rd_first(src, a) ___read(bpf_core_read, &__t, ___type(src), src, a);
	#define ___rd_last(...) \
	___read(bpf_core_read, &__t, \
	___type(___nolast(__VA_ARGS__)), __t, ___last(__VA_ARGS__));
	#define ___rd_p1(...) const void *__t; ___rd_first(__VA_ARGS__)
	#define ___rd_p2(...) ___rd_p1(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
	#define ___rd_p3(...) ___rd_p2(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
	#define ___rd_p4(...) ___rd_p3(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
	#define ___rd_p5(...) ___rd_p4(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
	#define ___rd_p6(...) ___rd_p5(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
	#define ___rd_p7(...) ___rd_p6(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
	#define ___rd_p8(...) ___rd_p7(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
	#define ___rd_p9(...) ___rd_p8(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
	#define ___read_ptrs(src, ...) \
	___apply(___rd_p, ___narg(__VA_ARGS__))(src, __VA_ARGS__)

	#define ___core_read0(fn, dst, src, a) \
	___read(fn, dst, ___type(src), src, a);
	#define ___core_readN(fn, dst, src, ...) \
	___read_ptrs(src, ___nolast(__VA_ARGS__)) \
	___read(fn, dst, ___type(src, ___nolast(__VA_ARGS__)), __t, \
	___last(__VA_ARGS__));
	#define ___core_read(fn, dst, src, a, ...) \
	___apply(___core_read, ___empty(__VA_ARGS__))(fn, dst, \
	src, a, ##__VA_ARGS__)

	/*
	* BPF_CORE_READ_INTO() is a more performance-conscious variant of
	* BPF_CORE_READ(), in which final field is read into user-provided storage.
	* See BPF_CORE_READ() below for more details on general usage.
	*/
	#define BPF_CORE_READ_INTO(dst, src, a, ...) \
	({ \
	___core_read(bpf_core_read, dst, src, a, ##__VA_ARGS__) \
	})

	/*
	* BPF_CORE_READ_STR_INTO() does same "pointer chasing" as
	* BPF_CORE_READ() for intermediate pointers, but then executes (and returns
	* corresponding error code) bpf_core_read_str() for final string read.
	*/
	#define BPF_CORE_READ_STR_INTO(dst, src, a, ...) \
	({ \
	___core_read(bpf_core_read_str, dst, src, a, ##__VA_ARGS__) \
	})

	/*
	* BPF_CORE_READ() is used to simplify BPF CO-RE relocatable read, especially
	* when there are few pointer chasing steps.
	* E.g., what in non-BPF world (or in BPF w/ BCC) would be something like:
	* int x = s->a.b.c->d.e->f->g;
	* can be succinctly achieved using BPF_CORE_READ as:
	* int x = BPF_CORE_READ(s, a.b.c, d.e, f, g);
	*
	* BPF_CORE_READ will decompose above statement into 4 bpf_core_read (BPF
	* CO-RE relocatable bpf_probe_read() wrapper) calls, logically equivalent to:
	* 1. const void *__t = s->a.b.c;
	* 2. __t = __t->d.e;
	* 3. __t = __t->f;
	* 4. return __t->g;
	*
	* Equivalence is logical, because there is a heavy type casting/preservation
	* involved, as well as all the reads are happening through bpf_probe_read()
	* calls using __builtin_preserve_access_index() to emit CO-RE relocations.
	*
	* N.B. Only up to 9 "field accessors" are supported, which should be more
	* than enough for any practical purpose.
	*/
	#define BPF_CORE_READ(src, a, ...) \
	({ \
	___type(src, a, ##__VA_ARGS__) __r; \
	BPF_CORE_READ_INTO(&__r, src, a, ##__VA_ARGS__); \
	__r; \
	})

	#endif