Tutorial: advanced BTF example

advanced02-BTF/Makefile

@@ -0,0 +1,48 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+
+XDP_BTF_TARGETS := xdp_prog_kern
+XDP_BTF_OBJ = ${XDP_BTF_TARGETS:=.o}
+
+_all: llvm-check pahole-check $(XDP_BTF_OBJ) xdp_loader
+
+COPY_LOADER := xdp_loader
+
+COMMON_DIR = ../common/
+include $(COMMON_DIR)/common.mk
+
+PAHOLE ?= pahole
+
+.PHONY: $(PAHOLE)
+
+TEST_PAHOLE := "$(PAHOLE) --help 2>&1 | grep BTF"
+
+pahole-check: $(PAHOLE)
+	@for TOOL in $^ ; do \
+		if [ ! $$(command -v $${TOOL} 2>/dev/null) ]; then \
+			echo "*** ERROR: Cannot find tool $${TOOL}" ;\
+			exit 1; \
+		else true; fi; \
+	done
+	@if [ ! $(TEST_PAHOLE) > /dev/null 2>&1 ]; then \
+		echo "Tool pahole too old, missing BTF support" ;\
+		exit 1; \
+	else \
+		echo "Using pahole to encode BTF info in ELF-object"; \
+	fi
+
+#LLC_FLAGS += -mcpu=probe
+LLC_FLAGS += -mattr=dwarfris
+
+$(XDP_BTF_OBJ): %.o: %.c  Makefile $(COMMON_MK)
+	$(CLANG) -S \
+	    -target bpf \
+	    -D __BPF_TRACING__ \
+	    $(CFLAGS) \
+	    -Wall \
+	    -Wno-unused-value \
+	    -Wno-pointer-sign \
+	    -Wno-compare-distinct-pointer-types \
+	    -Werror \
+	    -O2 -emit-llvm -c -g $<
+	$(LLC) -march=bpf $(LLC_FLAGS) -filetype=obj -o $@ ${@:.o=.ll}
+	$(PAHOLE) -V --btf_encode $@ > ${@:.o=.pahole-btf-info}

advanced02-BTF/common_kern_user.h

@@ -0,0 +1,17 @@
+/* This common_kern_user.h is used by kernel side BPF-progs and
+ * userspace programs, for sharing common struct's and DEFINEs.
+ */
+#ifndef __COMMON_KERN_USER_H
+#define __COMMON_KERN_USER_H
+
+/* This is the data record stored in the map */
+struct datarec {
+	__u64 rx_packets;
+	__u64 rx_bytes;
+};
+
+#ifndef XDP_ACTION_MAX
+#define XDP_ACTION_MAX (XDP_REDIRECT + 1)
+#endif
+
+#endif /* __COMMON_KERN_USER_H */

advanced02-BTF/xdp_prog_kern.c

@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/bpf.h>
+#include "bpf_helpers.h"
+
+#include "common_kern_user.h" /* defines: struct datarec; */
+
+#define _BPF_ANNOTATE_KV_PAIR(name, type_key, type_val)		\
+	struct ____btf_map_##name {					\
+		type_key key;						\
+		type_val value;					\
+	};								\
+	struct ____btf_map_##name					\
+	__attribute__ ((section(".maps." #name), used))		\
+		____btf_map_##name = { }
+
+struct bpf_map_def SEC("maps") xdp_stats_map = {
+	.type        = BPF_MAP_TYPE_PERCPU_ARRAY,
+	.key_size    = sizeof(__u32),
+	.value_size  = sizeof(struct datarec),
+	.max_entries = XDP_ACTION_MAX,
+};
+_BPF_ANNOTATE_KV_PAIR(xdp_stats_map, int, struct datarec);
+
+static __always_inline
+__u32 record_xdp_stats_action(struct xdp_md *ctx, __u32 action)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data     = (void *)(long)ctx->data;
+
+	if (action >= XDP_ACTION_MAX)
+		return XDP_ABORTED;
+
+	/* Lookup in kernel BPF-side return pointer to actual data record */
+	struct datarec *rec = bpf_map_lookup_elem(&xdp_stats_map, &action);
+	if (!rec)
+		return XDP_ABORTED;
+
+	/* Calculate packet length */
+	__u64 bytes = data_end - data;
+
+	/* BPF_MAP_TYPE_PERCPU_ARRAY returns a data record specific to current
+	 * CPU and XDP hooks runs under Softirq, which makes it safe to update
+	 * without atomic operations.
+	 */
+	rec->rx_packets++;
+	rec->rx_bytes += bytes;
+
+	return action;
+}
+
+SEC("xdp_pass")
+int  xdp_pass_func(struct xdp_md *ctx)
+{
+	__u32 action = XDP_PASS; /* XDP_PASS = 2 */
+
+	return record_xdp_stats_action(ctx, action);
+}
+
+char _license[] SEC("license") = "GPL";

headers/bpf_helpers.h

@@ -88,6 +88,15 @@ struct bpf_map_def {
 	unsigned int inner_map_idx;
 };
 
+#define BPF_ANNOTATE_KV_PAIR(name, type_key, type_val)		\
+	struct ____btf_map_##name {				\
+		type_key key;					\
+		type_val value;					\
+	};							\
+	struct ____btf_map_##name				\
+	__attribute__ ((section(".maps." #name), used))		\
+		____btf_map_##name = { }
+
 static int (*bpf_skb_load_bytes)(void *ctx, int off, void *to, int len) =
 	(void *) BPF_FUNC_skb_load_bytes;
 static int (*bpf_skb_store_bytes)(void *ctx, int off, void *from, int len, int flags) =