linux/tools/testing/selftests/bpf/progs/bpf_iter_test_kern6.c

// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2020 Facebook */
#include "bpf_iter.h"
#include <bpf/bpf_helpers.h>

char _license[] SEC("license") = "GPL";

__u32 value_sum = 0;

SEC("iter/bpf_map_elem")
int dump_bpf_hash_map(struct bpf_iter__bpf_map_elem *ctx)
{
	void *value = ctx->value;

	if (value == (void *)0)
		return 0;

	/* negative offset, verifier failure. */
	value_sum += *(__u32 *)(value - 4);
	return 0;
}