From: Andrii Nakryiko <andrii@kernel.org>
Date: Sun, 8 May 2022 17:41:44 -0700
Subject: libbpf: Complete field-based CO-RE helpers with field offset helper
Patch-mainline: v5.19-rc1
Git-commit: 7715f549a9d80a82428a7925fa4a00518c53c35c
References: jsc#PED-1377

Add bpf_core_field_offset() helper to complete field-based CO-RE
helpers. This helper can be useful for feature-detection and for some
more advanced cases of field reading (e.g., reading flexible array members).

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20220509004148.1801791-6-andrii@kernel.org
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 tools/lib/bpf/bpf_core_read.h |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/tools/lib/bpf/bpf_core_read.h
+++ b/tools/lib/bpf/bpf_core_read.h
@@ -144,6 +144,18 @@ enum bpf_enum_value_kind {
 	__builtin_preserve_field_info(___bpf_field_ref(field), BPF_FIELD_BYTE_SIZE)
 
 /*
+ * Convenience macro to get field's byte offset.
+ *
+ * Supports two forms:
+ *   - field reference through variable access:
+ *     bpf_core_field_offset(p->my_field);
+ *   - field reference through type and field names:
+ *     bpf_core_field_offset(struct my_type, my_field).
+ */
+#define bpf_core_field_offset(field...)					    \
+	__builtin_preserve_field_info(___bpf_field_ref(field), BPF_FIELD_BYTE_OFFSET)
+
+/*
  * Convenience macro to get BTF type ID of a specified type, using a local BTF
  * information. Return 32-bit unsigned integer with type ID from program's own
  * BTF. Always succeeds.