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libbpf: Add non-CO-RE variants of BPF_CORE_READ() macro family

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BPF_CORE_READ(), in addition to handling CO-RE relocations, also allows much
nicer way to read data structures with nested pointers. Instead of writing
a sequence of bpf_probe_read() calls to follow links, one can just write
BPF_CORE_READ(a, b, c, d) to effectively do a->b->c->d read. This is a welcome
ability when porting BCC code, which (in most cases) allows exactly the
intuitive a->b->c->d variant.

This patch adds non-CO-RE variants of BPF_CORE_READ() family of macros for
cases where CO-RE is not supported (e.g., old kernels). In such cases, the
property of shortening a sequence of bpf_probe_read()s to a simple
BPF_PROBE_READ(a, b, c, d) invocation is still desirable, especially when
porting BCC code to libbpf. Yet, no CO-RE relocation is going to be emitted.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20201218235614.2284956-3-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Andrii Nakryiko 2020-12-18 15:56:13 -08:00 committed by Alexei Starovoitov
parent 792001f4f7
commit a4b09a9ef9
1 changed files with 38 additions and 0 deletions
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38
tools/lib/bpf/bpf_core_read.h
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@ -308,6 +308,18 @@ enum bpf_enum_value_kind {
dst, (src), a, ##__VA_ARGS__) \
})
/* Non-CO-RE variant of BPF_CORE_READ_INTO() */
#define BPF_PROBE_READ_INTO(dst, src, a, ...) ({ \
___core_read(bpf_probe_read, bpf_probe_read, \
dst, (src), a, ##__VA_ARGS__) \
})
/* Non-CO-RE variant of BPF_CORE_READ_USER_INTO() */
#define BPF_PROBE_READ_USER_INTO(dst, src, a, ...) ({ \
___core_read(bpf_probe_read_user, bpf_probe_read_user, \
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
@ -324,6 +336,18 @@ enum bpf_enum_value_kind {
dst, (src), a, ##__VA_ARGS__) \
})
/* Non-CO-RE variant of BPF_CORE_READ_STR_INTO() */
#define BPF_PROBE_READ_STR_INTO(dst, src, a, ...) ({ \
___core_read(bpf_probe_read_str, bpf_probe_read, \
dst, (src), a, ##__VA_ARGS__) \
})
/* Non-CO-RE variant of BPF_CORE_READ_USER_STR_INTO() */
#define BPF_PROBE_READ_USER_STR_INTO(dst, src, a, ...) ({ \
___core_read(bpf_probe_read_user_str, bpf_probe_read_user, \
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.
@ -361,5 +385,19 @@ enum bpf_enum_value_kind {
__r; \
})
/* Non-CO-RE variant of BPF_CORE_READ() */
#define BPF_PROBE_READ(src, a, ...) ({ \
___type((src), a, ##__VA_ARGS__) __r; \
BPF_PROBE_READ_INTO(&__r, (src), a, ##__VA_ARGS__); \
__r; \
})
/* Non-CO-RE variant of BPF_CORE_READ_USER() */
#define BPF_PROBE_READ_USER(src, a, ...) ({ \
___type((src), a, ##__VA_ARGS__) __r; \
BPF_PROBE_READ_USER_INTO(&__r, (src), a, ##__VA_ARGS__); \
__r; \
})
#endif