Allow to specify field reference in two ways:
- if user has variable of necessary type, they can use variable-based
reference (my_var.my_field or my_var_ptr->my_field). This was the
only supported syntax up till now.
- now, bpf_core_field_exists() and bpf_core_field_size() support also
specifying field in a fashion similar to offsetof() macro, by
specifying type of the containing struct/union separately and field
name separately: bpf_core_field_exists(struct my_type, my_field).
This forms is quite often more convenient in practice and it matches
type-based CO-RE helpers that support specifying type by its name
without requiring any variables.
Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
tools/lib/bpf/bpf_core_read.h | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)
diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h
index e4aa9996a550..5ad415f9051f 100644
--- a/tools/lib/bpf/bpf_core_read.h
+++ b/tools/lib/bpf/bpf_core_read.h
@@ -110,21 +110,38 @@ enum bpf_enum_value_kind {
val; \
})
+#define ___bpf_field_ref1(field) (field)
+#define ___bpf_field_ref2(type, field) (((typeof(type) *)0)->field)
+#define ___bpf_field_ref(args...) \
+ ___bpf_apply(___bpf_field_ref, ___bpf_narg(args))(args)
+
/*
* 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.
+ *
+ * Supports two forms:
+ * - field reference through variable access:
+ * bpf_core_field_exists(p->my_field);
+ * - field reference through type and field names:
+ * bpf_core_field_exists(struct my_type, my_field).
*/
-#define bpf_core_field_exists(field) \
- __builtin_preserve_field_info(field, BPF_FIELD_EXISTS)
+#define bpf_core_field_exists(field...) \
+ __builtin_preserve_field_info(___bpf_field_ref(field), BPF_FIELD_EXISTS)
/*
* Convenience macro to get the byte size of a field. Works for integers,
* struct/unions, pointers, arrays, and enums.
+ *
+ * Supports two forms:
+ * - field reference through variable access:
+ * bpf_core_field_size(p->my_field);
+ * - field reference through type and field names:
+ * bpf_core_field_size(struct my_type, my_field).
*/
-#define bpf_core_field_size(field) \
- __builtin_preserve_field_info(field, BPF_FIELD_BYTE_SIZE)
+#define bpf_core_field_size(field...) \
+ __builtin_preserve_field_info(___bpf_field_ref(field), BPF_FIELD_BYTE_SIZE)
/*
* Convenience macro to get BTF type ID of a specified type, using a local BTF
--
2.30.2
