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ed57802121
Streamline BPF_CORE_READ_BITFIELD_PROBED interface to follow BPF_CORE_READ_BITFIELD (direct) and BPF_CORE_READ, in general, i.e., just return read result or 0, if underlying bpf_probe_read() failed. In practice, real applications rarely check bpf_probe_read() result, because it has to always work or otherwise it's a bug. So propagating internal bpf_probe_read() error from this macro hurts usability without providing real benefits in practice. This patch fixes the issue and simplifies usage, noticeable even in selftest itself. Signed-off-by: Andrii Nakryiko <andriin@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20191106201500.2582438-1-andriin@fb.com
264 lines
11 KiB
C
264 lines
11 KiB
C
/* SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause) */
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#ifndef __BPF_CORE_READ_H__
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#define __BPF_CORE_READ_H__
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/*
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* enum bpf_field_info_kind is passed as a second argument into
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* __builtin_preserve_field_info() built-in to get a specific aspect of
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* a field, captured as a first argument. __builtin_preserve_field_info(field,
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* info_kind) returns __u32 integer and produces BTF field relocation, which
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* is understood and processed by libbpf during BPF object loading. See
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* selftests/bpf for examples.
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*/
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enum bpf_field_info_kind {
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BPF_FIELD_BYTE_OFFSET = 0, /* field byte offset */
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BPF_FIELD_BYTE_SIZE = 1,
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BPF_FIELD_EXISTS = 2, /* field existence in target kernel */
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BPF_FIELD_SIGNED = 3,
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BPF_FIELD_LSHIFT_U64 = 4,
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BPF_FIELD_RSHIFT_U64 = 5,
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};
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#define __CORE_RELO(src, field, info) \
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__builtin_preserve_field_info((src)->field, BPF_FIELD_##info)
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#if __BYTE_ORDER == __LITTLE_ENDIAN
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#define __CORE_BITFIELD_PROBE_READ(dst, src, fld) \
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bpf_probe_read((void *)dst, \
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__CORE_RELO(src, fld, BYTE_SIZE), \
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(const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
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#else
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/* semantics of LSHIFT_64 assumes loading values into low-ordered bytes, so
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* for big-endian we need to adjust destination pointer accordingly, based on
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* field byte size
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*/
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#define __CORE_BITFIELD_PROBE_READ(dst, src, fld) \
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bpf_probe_read((void *)dst + (8 - __CORE_RELO(src, fld, BYTE_SIZE)), \
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__CORE_RELO(src, fld, BYTE_SIZE), \
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(const void *)src + __CORE_RELO(src, fld, BYTE_OFFSET))
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#endif
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/*
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* Extract bitfield, identified by s->field, and return its value as u64.
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* All this is done in relocatable manner, so bitfield changes such as
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* signedness, bit size, offset changes, this will be handled automatically.
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* This version of macro is using bpf_probe_read() to read underlying integer
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* storage. Macro functions as an expression and its return type is
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* bpf_probe_read()'s return value: 0, on success, <0 on error.
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*/
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#define BPF_CORE_READ_BITFIELD_PROBED(s, field) ({ \
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unsigned long long val = 0; \
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\
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__CORE_BITFIELD_PROBE_READ(&val, s, field); \
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val <<= __CORE_RELO(s, field, LSHIFT_U64); \
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if (__CORE_RELO(s, field, SIGNED)) \
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val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64); \
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else \
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val = val >> __CORE_RELO(s, field, RSHIFT_U64); \
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val; \
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})
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/*
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* Extract bitfield, identified by s->field, and return its value as u64.
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* This version of macro is using direct memory reads and should be used from
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* BPF program types that support such functionality (e.g., typed raw
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* tracepoints).
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*/
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#define BPF_CORE_READ_BITFIELD(s, field) ({ \
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const void *p = (const void *)s + __CORE_RELO(s, field, BYTE_OFFSET); \
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unsigned long long val; \
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\
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switch (__CORE_RELO(s, field, BYTE_SIZE)) { \
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case 1: val = *(const unsigned char *)p; \
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case 2: val = *(const unsigned short *)p; \
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case 4: val = *(const unsigned int *)p; \
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case 8: val = *(const unsigned long long *)p; \
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} \
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val <<= __CORE_RELO(s, field, LSHIFT_U64); \
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if (__CORE_RELO(s, field, SIGNED)) \
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val = ((long long)val) >> __CORE_RELO(s, field, RSHIFT_U64); \
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else \
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val = val >> __CORE_RELO(s, field, RSHIFT_U64); \
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val; \
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})
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/*
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* Convenience macro to check that field actually exists in target kernel's.
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* Returns:
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* 1, if matching field is present in target kernel;
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* 0, if no matching field found.
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*/
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#define bpf_core_field_exists(field) \
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__builtin_preserve_field_info(field, BPF_FIELD_EXISTS)
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/*
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* Convenience macro to get byte size of a field. Works for integers,
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* struct/unions, pointers, arrays, and enums.
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*/
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#define bpf_core_field_size(field) \
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__builtin_preserve_field_info(field, BPF_FIELD_BYTE_SIZE)
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/*
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* bpf_core_read() abstracts away bpf_probe_read() call and captures offset
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* relocation for source address using __builtin_preserve_access_index()
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* built-in, provided by Clang.
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*
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* __builtin_preserve_access_index() takes as an argument an expression of
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* taking an address of a field within struct/union. It makes compiler emit
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* a relocation, which records BTF type ID describing root struct/union and an
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* accessor string which describes exact embedded field that was used to take
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* an address. See detailed description of this relocation format and
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* semantics in comments to struct bpf_field_reloc in libbpf_internal.h.
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*
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* This relocation allows libbpf to adjust BPF instruction to use correct
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* actual field offset, based on target kernel BTF type that matches original
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* (local) BTF, used to record relocation.
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*/
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#define bpf_core_read(dst, sz, src) \
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bpf_probe_read(dst, sz, \
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(const void *)__builtin_preserve_access_index(src))
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/*
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* bpf_core_read_str() is a thin wrapper around bpf_probe_read_str()
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* additionally emitting BPF CO-RE field relocation for specified source
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* argument.
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*/
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#define bpf_core_read_str(dst, sz, src) \
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bpf_probe_read_str(dst, sz, \
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(const void *)__builtin_preserve_access_index(src))
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#define ___concat(a, b) a ## b
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#define ___apply(fn, n) ___concat(fn, n)
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#define ___nth(_1, _2, _3, _4, _5, _6, _7, _8, _9, _10, __11, N, ...) N
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/*
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* return number of provided arguments; used for switch-based variadic macro
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* definitions (see ___last, ___arrow, etc below)
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*/
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#define ___narg(...) ___nth(_, ##__VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
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/*
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* return 0 if no arguments are passed, N - otherwise; used for
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* recursively-defined macros to specify termination (0) case, and generic
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* (N) case (e.g., ___read_ptrs, ___core_read)
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*/
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#define ___empty(...) ___nth(_, ##__VA_ARGS__, N, N, N, N, N, N, N, N, N, N, 0)
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#define ___last1(x) x
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#define ___last2(a, x) x
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#define ___last3(a, b, x) x
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#define ___last4(a, b, c, x) x
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#define ___last5(a, b, c, d, x) x
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#define ___last6(a, b, c, d, e, x) x
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#define ___last7(a, b, c, d, e, f, x) x
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#define ___last8(a, b, c, d, e, f, g, x) x
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#define ___last9(a, b, c, d, e, f, g, h, x) x
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#define ___last10(a, b, c, d, e, f, g, h, i, x) x
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#define ___last(...) ___apply(___last, ___narg(__VA_ARGS__))(__VA_ARGS__)
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#define ___nolast2(a, _) a
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#define ___nolast3(a, b, _) a, b
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#define ___nolast4(a, b, c, _) a, b, c
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#define ___nolast5(a, b, c, d, _) a, b, c, d
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#define ___nolast6(a, b, c, d, e, _) a, b, c, d, e
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#define ___nolast7(a, b, c, d, e, f, _) a, b, c, d, e, f
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#define ___nolast8(a, b, c, d, e, f, g, _) a, b, c, d, e, f, g
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#define ___nolast9(a, b, c, d, e, f, g, h, _) a, b, c, d, e, f, g, h
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#define ___nolast10(a, b, c, d, e, f, g, h, i, _) a, b, c, d, e, f, g, h, i
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#define ___nolast(...) ___apply(___nolast, ___narg(__VA_ARGS__))(__VA_ARGS__)
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#define ___arrow1(a) a
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#define ___arrow2(a, b) a->b
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#define ___arrow3(a, b, c) a->b->c
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#define ___arrow4(a, b, c, d) a->b->c->d
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#define ___arrow5(a, b, c, d, e) a->b->c->d->e
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#define ___arrow6(a, b, c, d, e, f) a->b->c->d->e->f
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#define ___arrow7(a, b, c, d, e, f, g) a->b->c->d->e->f->g
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#define ___arrow8(a, b, c, d, e, f, g, h) a->b->c->d->e->f->g->h
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#define ___arrow9(a, b, c, d, e, f, g, h, i) a->b->c->d->e->f->g->h->i
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#define ___arrow10(a, b, c, d, e, f, g, h, i, j) a->b->c->d->e->f->g->h->i->j
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#define ___arrow(...) ___apply(___arrow, ___narg(__VA_ARGS__))(__VA_ARGS__)
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#define ___type(...) typeof(___arrow(__VA_ARGS__))
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#define ___read(read_fn, dst, src_type, src, accessor) \
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read_fn((void *)(dst), sizeof(*(dst)), &((src_type)(src))->accessor)
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/* "recursively" read a sequence of inner pointers using local __t var */
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#define ___rd_first(src, a) ___read(bpf_core_read, &__t, ___type(src), src, a);
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#define ___rd_last(...) \
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___read(bpf_core_read, &__t, \
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___type(___nolast(__VA_ARGS__)), __t, ___last(__VA_ARGS__));
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#define ___rd_p1(...) const void *__t; ___rd_first(__VA_ARGS__)
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#define ___rd_p2(...) ___rd_p1(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
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#define ___rd_p3(...) ___rd_p2(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
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#define ___rd_p4(...) ___rd_p3(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
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#define ___rd_p5(...) ___rd_p4(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
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#define ___rd_p6(...) ___rd_p5(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
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#define ___rd_p7(...) ___rd_p6(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
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#define ___rd_p8(...) ___rd_p7(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
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#define ___rd_p9(...) ___rd_p8(___nolast(__VA_ARGS__)) ___rd_last(__VA_ARGS__)
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#define ___read_ptrs(src, ...) \
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___apply(___rd_p, ___narg(__VA_ARGS__))(src, __VA_ARGS__)
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#define ___core_read0(fn, dst, src, a) \
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___read(fn, dst, ___type(src), src, a);
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#define ___core_readN(fn, dst, src, ...) \
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___read_ptrs(src, ___nolast(__VA_ARGS__)) \
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___read(fn, dst, ___type(src, ___nolast(__VA_ARGS__)), __t, \
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___last(__VA_ARGS__));
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#define ___core_read(fn, dst, src, a, ...) \
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___apply(___core_read, ___empty(__VA_ARGS__))(fn, dst, \
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src, a, ##__VA_ARGS__)
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/*
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* BPF_CORE_READ_INTO() is a more performance-conscious variant of
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* BPF_CORE_READ(), in which final field is read into user-provided storage.
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* See BPF_CORE_READ() below for more details on general usage.
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*/
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#define BPF_CORE_READ_INTO(dst, src, a, ...) \
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({ \
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___core_read(bpf_core_read, dst, src, a, ##__VA_ARGS__) \
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})
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/*
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* BPF_CORE_READ_STR_INTO() does same "pointer chasing" as
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* BPF_CORE_READ() for intermediate pointers, but then executes (and returns
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* corresponding error code) bpf_core_read_str() for final string read.
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*/
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#define BPF_CORE_READ_STR_INTO(dst, src, a, ...) \
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({ \
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___core_read(bpf_core_read_str, dst, src, a, ##__VA_ARGS__) \
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})
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/*
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* BPF_CORE_READ() is used to simplify BPF CO-RE relocatable read, especially
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* when there are few pointer chasing steps.
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* E.g., what in non-BPF world (or in BPF w/ BCC) would be something like:
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* int x = s->a.b.c->d.e->f->g;
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* can be succinctly achieved using BPF_CORE_READ as:
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* int x = BPF_CORE_READ(s, a.b.c, d.e, f, g);
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*
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* BPF_CORE_READ will decompose above statement into 4 bpf_core_read (BPF
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* CO-RE relocatable bpf_probe_read() wrapper) calls, logically equivalent to:
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* 1. const void *__t = s->a.b.c;
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* 2. __t = __t->d.e;
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* 3. __t = __t->f;
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* 4. return __t->g;
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*
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* Equivalence is logical, because there is a heavy type casting/preservation
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* involved, as well as all the reads are happening through bpf_probe_read()
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* calls using __builtin_preserve_access_index() to emit CO-RE relocations.
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*
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* N.B. Only up to 9 "field accessors" are supported, which should be more
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* than enough for any practical purpose.
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*/
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#define BPF_CORE_READ(src, a, ...) \
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({ \
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___type(src, a, ##__VA_ARGS__) __r; \
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BPF_CORE_READ_INTO(&__r, src, a, ##__VA_ARGS__); \
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__r; \
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})
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#endif
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