From a4b09a9ef9451b09d87550720f8db3ae280b3eea Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Fri, 18 Dec 2020 15:56:13 -0800 Subject: [PATCH] libbpf: Add non-CO-RE variants of BPF_CORE_READ() macro family 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 Signed-off-by: Daniel Borkmann Link: https://lore.kernel.org/bpf/20201218235614.2284956-3-andrii@kernel.org Signed-off-by: Alexei Starovoitov --- tools/lib/bpf/bpf_core_read.h | 38 +++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h index db0c735ceb53b..9456aabcb03a2 100644 --- a/tools/lib/bpf/bpf_core_read.h +++ b/tools/lib/bpf/bpf_core_read.h @@ -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 -- 2.30.2