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@xxxxxxxxxx>
---
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 db0c735ceb53..9456aabcb03a 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
--
2.24.1
