From c2376051362e9d4a2718421dd050cf1c01dc6ab9 Mon Sep 17 00:00:00 2001
From: Bernhard Kaindl <bernhardkaindl7@gmail.com>
Date: Fri, 3 May 2024 12:00:00 +0000
Subject: [PATCH] libbpf tcptop: Fix "unrecognized bpf_ld_imm64 insn" on 4.19

Fix the BPF load error `unrecognized bpf_ld_imm64 insn`
on 4.19 by converting rodata config variables to a map.

tcptop can use CO-RE including 4.19 when a detached vmlinux BTF
file is provided, generated from a DWARF vmlinux using pahole:
pahole -J;objcopy --only-section=.BTF vmlinux /boot/vmlinux-$(uname -r)

Signed-off-by: Bernhard Kaindl <bernhardkaindl7@gmail.com>
---
 libbpf-tools/tcptop.bpf.c | 20 ++++++++++++++------
 libbpf-tools/tcptop.c     | 16 ++++++++++++----
 libbpf-tools/tcptop.h     |  6 ++++++
 3 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/libbpf-tools/tcptop.bpf.c b/libbpf-tools/tcptop.bpf.c
index 9c27ba485112..5c9eb5c7b8bf 100644
--- a/libbpf-tools/tcptop.bpf.c
+++ b/libbpf-tools/tcptop.bpf.c
@@ -12,9 +12,12 @@
 #define AF_INET		2	/* Internet IP Protocol 	*/
 #define AF_INET6	10	/* IP version 6			*/
 
-const volatile bool filter_cg = false;
-const volatile pid_t target_pid = -1;
-const volatile int target_family = -1;
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, u32);
+	__type(value, struct filter_cfg_t);
+} filter_cfg_map SEC(".maps");
 
 struct {
 	__uint(type, BPF_MAP_TYPE_CGROUP_ARRAY);
@@ -32,20 +35,25 @@ struct {
 
 static int probe_ip(bool receiving, struct sock *sk, size_t size)
 {
+	int zero = 0;
+	struct filter_cfg_t *args = bpf_map_lookup_elem(&filter_cfg_map, &zero);
+	if (!args)
+		return 0;
+
 	struct ip_key_t ip_key = {};
 	struct traffic_t *trafficp;
 	u16 family;
 	u32 pid;
 
-	if (filter_cg && !bpf_current_task_under_cgroup(&cgroup_map, 0))
+	if (args->filter_cg && !bpf_current_task_under_cgroup(&cgroup_map, 0))
 		return 0;
 
 	pid = bpf_get_current_pid_tgid() >> 32;
-	if (target_pid != -1 && target_pid != pid)
+	if (args->target_pid != -1 && args->target_pid != pid)
 		return 0;
 
 	family = BPF_CORE_READ(sk, __sk_common.skc_family);
-	if (target_family != -1 && target_family != family)
+	if (args->target_family != -1 && args->target_family != family)
 		return 0;
 
 	/* drop */
diff --git a/libbpf-tools/tcptop.c b/libbpf-tools/tcptop.c
index d19fb9397633..04a6ed5a012f 100644
--- a/libbpf-tools/tcptop.c
+++ b/libbpf-tools/tcptop.c
@@ -339,6 +339,7 @@ int main(int argc, char **argv)
 	struct tcptop_bpf *obj;
 	int family;
 	int cgfd = -1;
+	int zero = 0;
 	int err;
 
 	err = argp_parse(&argp, argc, argv, 0, NULL, NULL);
@@ -359,9 +360,11 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	obj->rodata->target_pid = target_pid;
-	obj->rodata->target_family = family;
-	obj->rodata->filter_cg = cgroup_filtering;
+	struct filter_cfg_t filter_cfg = {
+		.filter_cg = cgroup_filtering,
+		.target_pid = target_pid,
+		.target_family = family,
+	};
 
 	err = tcptop_bpf__load(obj);
 	if (err) {
@@ -369,8 +372,13 @@ int main(int argc, char **argv)
 		goto cleanup;
 	}
 
+	int filter_cfg_fd = bpf_map__fd(obj->maps.filter_cfg_map);
+	if (bpf_map_update_elem(filter_cfg_fd, &zero, &filter_cfg, BPF_ANY)) {
+		warn("Failed to update filter config map\n");
+		goto cleanup;
+	}
+
 	if (cgroup_filtering) {
-		int zero = 0;
 		int cg_map_fd = bpf_map__fd(obj->maps.cgroup_map);
 
 		cgfd = open(cgroup_path, O_RDONLY);
diff --git a/libbpf-tools/tcptop.h b/libbpf-tools/tcptop.h
index 9e086c744ec2..48809e8fd869 100644
--- a/libbpf-tools/tcptop.h
+++ b/libbpf-tools/tcptop.h
@@ -4,6 +4,12 @@
 
 #define TASK_COMM_LEN 16
 
+struct filter_cfg_t {
+        bool filter_cg;
+        pid_t target_pid;
+        int target_family;
+};
+
 struct ip_key_t {
 	unsigned __int128 saddr;
 	unsigned __int128 daddr;