Merge branch 'bpf_iter-fixes'

Yonghong Song says:

====================
Commit ae24345da54e ("bpf: Implement an interface to register
bpf_iter targets") and its subsequent commits in the same patch set
introduced bpf iterator, a way to run bpf program when iterating
kernel data structures.

This patch set addressed some followup issues. One big change
is to allow target to pass ctx arg register types to verifier
for verification purpose. Please see individual patch for details.

Changelogs:
  v1 -> v2:
    . add "const" qualifier to struct bpf_iter_reg for
      bpf_iter_[un]reg_target, and this results in
      additional "const" qualifiers in some other places
    . drop the patch which will issue WARN_ONCE if
      seq_ops->show() returns a positive value.
      If this does happen, code review should spot
      this or author does know what he is doing.
      In the future, we do want to implement a
      mechanism to find out all registered targets
      so we will be aware of new additions.
====================

Acked-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

15 files changed, 183 insertions, 86 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cf4b6e44f2bc..c45d198ac38c 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -643,6 +643,12 @@ struct bpf_jit_poke_descriptor {
 	u16 reason;
 };
 
+/* reg_type info for ctx arguments */
+struct bpf_ctx_arg_aux {
+	u32 offset;
+	enum bpf_reg_type reg_type;
+};
+
 struct bpf_prog_aux {
 	atomic64_t refcnt;
 	u32 used_map_cnt;
@@ -654,12 +660,13 @@ struct bpf_prog_aux {
 	u32 func_cnt; /* used by non-func prog as the number of func progs */
 	u32 func_idx; /* 0 for non-func prog, the index in func array for func prog */
 	u32 attach_btf_id; /* in-kernel BTF type id to attach to */
+	u32 ctx_arg_info_size;
+	const struct bpf_ctx_arg_aux *ctx_arg_info;
 	struct bpf_prog *linked_prog;
 	bool verifier_zext; /* Zero extensions has been inserted by verifier. */
 	bool offload_requested;
 	bool attach_btf_trace; /* true if attaching to BTF-enabled raw tp */
 	bool func_proto_unreliable;
-	bool btf_id_or_null_non0_off;
 	enum bpf_tramp_prog_type trampoline_prog_type;
 	struct bpf_trampoline *trampoline;
 	struct hlist_node tramp_hlist;
@@ -1131,20 +1138,23 @@ struct bpf_link *bpf_link_get_from_fd(u32 ufd);
 int bpf_obj_pin_user(u32 ufd, const char __user *pathname);
 int bpf_obj_get_user(const char __user *pathname, int flags);
 
-#define BPF_ITER_FUNC_PREFIX "__bpf_iter__"
+#define BPF_ITER_FUNC_PREFIX "bpf_iter_"
 #define DEFINE_BPF_ITER_FUNC(target, args...)			\
-	extern int __bpf_iter__ ## target(args);		\
-	int __init __bpf_iter__ ## target(args) { return 0; }
+	extern int bpf_iter_ ## target(args);			\
+	int __init bpf_iter_ ## target(args) { return 0; }
 
 typedef int (*bpf_iter_init_seq_priv_t)(void *private_data);
 typedef void (*bpf_iter_fini_seq_priv_t)(void *private_data);
 
+#define BPF_ITER_CTX_ARG_MAX 2
 struct bpf_iter_reg {
 	const char *target;
 	const struct seq_operations *seq_ops;
 	bpf_iter_init_seq_priv_t init_seq_private;
 	bpf_iter_fini_seq_priv_t fini_seq_private;
 	u32 seq_priv_size;
+	u32 ctx_arg_info_size;
+	struct bpf_ctx_arg_aux ctx_arg_info[BPF_ITER_CTX_ARG_MAX];
 };
 
 struct bpf_iter_meta {
@@ -1153,8 +1163,8 @@ struct bpf_iter_meta {
 	u64 seq_num;
 };
 
-int bpf_iter_reg_target(struct bpf_iter_reg *reg_info);
-void bpf_iter_unreg_target(const char *target);
+int bpf_iter_reg_target(const struct bpf_iter_reg *reg_info);
+void bpf_iter_unreg_target(const struct bpf_iter_reg *reg_info);
 bool bpf_iter_prog_supported(struct bpf_prog *prog);
 int bpf_iter_link_attach(const union bpf_attr *attr, struct bpf_prog *prog);
 int bpf_iter_new_fd(struct bpf_link *link);
diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 80262d2980f5..870b646c5797 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -540,6 +540,13 @@ static inline bool fib6_metric_locked(struct fib6_info *f6i, int metric)
 	return !!(f6i->fib6_metrics->metrics[RTAX_LOCK - 1] & (1 << metric));
 }
 
+#if IS_BUILTIN(CONFIG_IPV6) && defined(CONFIG_BPF_SYSCALL)
+struct bpf_iter__ipv6_route {
+	__bpf_md_ptr(struct bpf_iter_meta *, meta);
+	__bpf_md_ptr(struct fib6_info *, rt);
+};
+#endif
+
 #ifdef CONFIG_IPV6_MULTIPLE_TABLES
 static inline bool fib6_has_custom_rules(const struct net *net)
 {
diff --git a/kernel/bpf/bpf_iter.c b/kernel/bpf/bpf_iter.c
index 30efd15cd4a0..dd612b80b9fe 100644
--- a/kernel/bpf/bpf_iter.c
+++ b/kernel/bpf/bpf_iter.c
@@ -8,11 +8,7 @@
 
 struct bpf_iter_target_info {
 	struct list_head list;
-	const char *target;
-	const struct seq_operations *seq_ops;
-	bpf_iter_init_seq_priv_t init_seq_private;
-	bpf_iter_fini_seq_priv_t fini_seq_private;
-	u32 seq_priv_size;
+	const struct bpf_iter_reg *reg_info;
 	u32 btf_id;	/* cached value */
 };
 
@@ -222,8 +218,8 @@ static int iter_release(struct inode *inode, struct file *file)
 	iter_priv = container_of(seq->private, struct bpf_iter_priv_data,
 				 target_private);
 
-	if (iter_priv->tinfo->fini_seq_private)
-		iter_priv->tinfo->fini_seq_private(seq->private);
+	if (iter_priv->tinfo->reg_info->fini_seq_private)
+		iter_priv->tinfo->reg_info->fini_seq_private(seq->private);
 
 	bpf_prog_put(iter_priv->prog);
 	seq->private = iter_priv;
@@ -238,7 +234,12 @@ const struct file_operations bpf_iter_fops = {
 	.release	= iter_release,
 };
 
-int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
+/* The argument reg_info will be cached in bpf_iter_target_info.
+ * The common practice is to declare target reg_info as
+ * a const static variable and passed as an argument to
+ * bpf_iter_reg_target().
+ */
+int bpf_iter_reg_target(const struct bpf_iter_reg *reg_info)
 {
 	struct bpf_iter_target_info *tinfo;
 
@@ -246,11 +247,7 @@ int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
 	if (!tinfo)
 		return -ENOMEM;
 
-	tinfo->target = reg_info->target;
-	tinfo->seq_ops = reg_info->seq_ops;
-	tinfo->init_seq_private = reg_info->init_seq_private;
-	tinfo->fini_seq_private = reg_info->fini_seq_private;
-	tinfo->seq_priv_size = reg_info->seq_priv_size;
+	tinfo->reg_info = reg_info;
 	INIT_LIST_HEAD(&tinfo->list);
 
 	mutex_lock(&targets_mutex);
@@ -260,14 +257,14 @@ int bpf_iter_reg_target(struct bpf_iter_reg *reg_info)
 	return 0;
 }
 
-void bpf_iter_unreg_target(const char *target)
+void bpf_iter_unreg_target(const struct bpf_iter_reg *reg_info)
 {
 	struct bpf_iter_target_info *tinfo;
 	bool found = false;
 
 	mutex_lock(&targets_mutex);
 	list_for_each_entry(tinfo, &targets, list) {
-		if (!strcmp(target, tinfo->target)) {
+		if (reg_info == tinfo->reg_info) {
 			list_del(&tinfo->list);
 			kfree(tinfo);
 			found = true;
@@ -303,7 +300,7 @@ bool bpf_iter_prog_supported(struct bpf_prog *prog)
 			supported = true;
 			break;
 		}
-		if (!strcmp(attach_fname + prefix_len, tinfo->target)) {
+		if (!strcmp(attach_fname + prefix_len, tinfo->reg_info->target)) {
 			cache_btf_id(tinfo, prog);
 			supported = true;
 			break;
@@ -311,6 +308,11 @@ bool bpf_iter_prog_supported(struct bpf_prog *prog)
 	}
 	mutex_unlock(&targets_mutex);
 
+	if (supported) {
+		prog->aux->ctx_arg_info_size = tinfo->reg_info->ctx_arg_info_size;
+		prog->aux->ctx_arg_info = tinfo->reg_info->ctx_arg_info;
+	}
+
 	return supported;
 }
 
@@ -431,15 +433,16 @@ static int prepare_seq_file(struct file *file, struct bpf_iter_link *link)
 
 	tinfo = link->tinfo;
 	total_priv_dsize = offsetof(struct bpf_iter_priv_data, target_private) +
-			   tinfo->seq_priv_size;
-	priv_data = __seq_open_private(file, tinfo->seq_ops, total_priv_dsize);
+			   tinfo->reg_info->seq_priv_size;
+	priv_data = __seq_open_private(file, tinfo->reg_info->seq_ops,
+				       total_priv_dsize);
 	if (!priv_data) {
 		err = -ENOMEM;
 		goto release_prog;
 	}
 
-	if (tinfo->init_seq_private) {
-		err = tinfo->init_seq_private(priv_data->target_private);
+	if (tinfo->reg_info->init_seq_private) {
+		err = tinfo->reg_info->init_seq_private(priv_data->target_private);
 		if (err)
 			goto release_seq_file;
 	}
@@ -526,5 +529,11 @@ int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx)
 	migrate_enable();
 	rcu_read_unlock();
 
+	/* bpf program can only return 0 or 1:
+	 *  0 : okay
+	 *  1 : retry the same object
+	 * The bpf_iter_run_prog() return value
+	 * will be seq_ops->show() return value.
+	 */
 	return ret == 0 ? 0 : -EAGAIN;
 }
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index dcd233139294..58c9af1d4808 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3694,7 +3694,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 	struct bpf_verifier_log *log = info->log;
 	const struct btf_param *args;
 	u32 nr_args, arg;
-	int ret;
+	int i, ret;
 
 	if (off % 8) {
 		bpf_log(log, "func '%s' offset %d is not multiple of 8\n",
@@ -3790,10 +3790,15 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 		return true;
 
 	/* this is a pointer to another type */
-	if (off != 0 && prog->aux->btf_id_or_null_non0_off)
-		info->reg_type = PTR_TO_BTF_ID_OR_NULL;
-	else
-		info->reg_type = PTR_TO_BTF_ID;
+	info->reg_type = PTR_TO_BTF_ID;
+	for (i = 0; i < prog->aux->ctx_arg_info_size; i++) {
+		const struct bpf_ctx_arg_aux *ctx_arg_info = &prog->aux->ctx_arg_info[i];
+
+		if (ctx_arg_info->offset == off) {
+			info->reg_type = ctx_arg_info->reg_type;
+			break;
+		}
+	}
 
 	if (tgt_prog) {
 		ret = btf_translate_to_vmlinux(log, btf, t, tgt_prog->type, arg);
diff --git a/kernel/bpf/map_iter.c b/kernel/bpf/map_iter.c
index 8162e0c00b9f..c69071e334bf 100644
--- a/kernel/bpf/map_iter.c
+++ b/kernel/bpf/map_iter.c
@@ -81,17 +81,22 @@ static const struct seq_operations bpf_map_seq_ops = {
 	.show	= bpf_map_seq_show,
 };
 
+static const struct bpf_iter_reg bpf_map_reg_info = {
+	.target			= "bpf_map",
+	.seq_ops		= &bpf_map_seq_ops,
+	.init_seq_private	= NULL,
+	.fini_seq_private	= NULL,
+	.seq_priv_size		= sizeof(struct bpf_iter_seq_map_info),
+	.ctx_arg_info_size	= 1,
+	.ctx_arg_info		= {
+		{ offsetof(struct bpf_iter__bpf_map, map),
+		  PTR_TO_BTF_ID_OR_NULL },
+	},
+};
+
 static int __init bpf_map_iter_init(void)
 {
-	struct bpf_iter_reg reg_info = {
-		.target			= "bpf_map",
-		.seq_ops		= &bpf_map_seq_ops,
-		.init_seq_private	= NULL,
-		.fini_seq_private	= NULL,
-		.seq_priv_size		= sizeof(struct bpf_iter_seq_map_info),
-	};
-
-	return bpf_iter_reg_target(&reg_info);
+	return bpf_iter_reg_target(&bpf_map_reg_info);
 }
 
 late_initcall(bpf_map_iter_init);
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index aeed662d8451..a9b7264dda08 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -306,22 +306,36 @@ static const struct seq_operations task_file_seq_ops = {
 	.show	= task_file_seq_show,
 };
 
+static const struct bpf_iter_reg task_reg_info = {
+	.target			= "task",
+	.seq_ops		= &task_seq_ops,
+	.init_seq_private	= init_seq_pidns,
+	.fini_seq_private	= fini_seq_pidns,
+	.seq_priv_size		= sizeof(struct bpf_iter_seq_task_info),
+	.ctx_arg_info_size	= 1,
+	.ctx_arg_info		= {
+		{ offsetof(struct bpf_iter__task, task),
+		  PTR_TO_BTF_ID_OR_NULL },
+	},
+};
+
+static const struct bpf_iter_reg task_file_reg_info = {
+	.target			= "task_file",
+	.seq_ops		= &task_file_seq_ops,
+	.init_seq_private	= init_seq_pidns,
+	.fini_seq_private	= fini_seq_pidns,
+	.seq_priv_size		= sizeof(struct bpf_iter_seq_task_file_info),
+	.ctx_arg_info_size	= 2,
+	.ctx_arg_info		= {
+		{ offsetof(struct bpf_iter__task_file, task),
+		  PTR_TO_BTF_ID_OR_NULL },
+		{ offsetof(struct bpf_iter__task_file, file),
+		  PTR_TO_BTF_ID_OR_NULL },
+	},
+};
+
 static int __init task_iter_init(void)
 {
-	struct bpf_iter_reg task_file_reg_info = {
-		.target			= "task_file",
-		.seq_ops		= &task_file_seq_ops,
-		.init_seq_private	= init_seq_pidns,
-		.fini_seq_private	= fini_seq_pidns,
-		.seq_priv_size		= sizeof(struct bpf_iter_seq_task_file_info),
-	};
-	struct bpf_iter_reg task_reg_info = {
-		.target			= "task",
-		.seq_ops		= &task_seq_ops,
-		.init_seq_private	= init_seq_pidns,
-		.fini_seq_private	= fini_seq_pidns,
-		.seq_priv_size		= sizeof(struct bpf_iter_seq_task_info),
-	};
 	int ret;
 
 	ret = bpf_iter_reg_target(&task_reg_info);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2a1826c76bb6..a3f2af756fd6 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -10652,7 +10652,6 @@ static int check_attach_btf_id(struct bpf_verifier_env *env)
 		prog->aux->attach_func_proto = t;
 		if (!bpf_iter_prog_supported(prog))
 			return -EINVAL;
-		prog->aux->btf_id_or_null_non0_off = true;
 		ret = btf_distill_func_proto(&env->log, btf, t,
 					     tname, &fmodel);
 		return ret;
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index a1fcc0ca21af..250ff52c674e 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -2638,11 +2638,6 @@ static void ipv6_route_native_seq_stop(struct seq_file *seq, void *v)
 }
 
 #if IS_BUILTIN(CONFIG_IPV6) && defined(CONFIG_BPF_SYSCALL)
-struct bpf_iter__ipv6_route {
-	__bpf_md_ptr(struct bpf_iter_meta *, meta);
-	__bpf_md_ptr(struct fib6_info *, rt);
-};
-
 static int ipv6_route_prog_seq_show(struct bpf_prog *prog,
 				    struct bpf_iter_meta *meta,
 				    void *v)
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 25f6d3e619d0..22e56465f14d 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -6397,22 +6397,27 @@ void __init ip6_route_init_special_entries(void)
 #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_PROC_FS)
 DEFINE_BPF_ITER_FUNC(ipv6_route, struct bpf_iter_meta *meta, struct fib6_info *rt)
 
+static const struct bpf_iter_reg ipv6_route_reg_info = {
+	.target			= "ipv6_route",
+	.seq_ops		= &ipv6_route_seq_ops,
+	.init_seq_private	= bpf_iter_init_seq_net,
+	.fini_seq_private	= bpf_iter_fini_seq_net,
+	.seq_priv_size		= sizeof(struct ipv6_route_iter),
+	.ctx_arg_info_size	= 1,
+	.ctx_arg_info		= {
+		{ offsetof(struct bpf_iter__ipv6_route, rt),
+		  PTR_TO_BTF_ID_OR_NULL },
+	},
+};
+
 static int __init bpf_iter_register(void)
 {
-	struct bpf_iter_reg reg_info = {
-		.target			= "ipv6_route",
-		.seq_ops		= &ipv6_route_seq_ops,
-		.init_seq_private	= bpf_iter_init_seq_net,
-		.fini_seq_private	= bpf_iter_fini_seq_net,
-		.seq_priv_size		= sizeof(struct ipv6_route_iter),
-	};
-
-	return bpf_iter_reg_target(&reg_info);
+	return bpf_iter_reg_target(&ipv6_route_reg_info);
 }
 
 static void bpf_iter_unregister(void)
 {
-	bpf_iter_unreg_target("ipv6_route");
+	bpf_iter_unreg_target(&ipv6_route_reg_info);
 }
 #endif
 #endif
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 33cda9baa979..4f2c3b14ddbf 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2803,17 +2803,22 @@ static const struct rhashtable_params netlink_rhashtable_params = {
 };
 
 #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_PROC_FS)
+static const struct bpf_iter_reg netlink_reg_info = {
+	.target			= "netlink",
+	.seq_ops		= &netlink_seq_ops,
+	.init_seq_private	= bpf_iter_init_seq_net,
+	.fini_seq_private	= bpf_iter_fini_seq_net,
+	.seq_priv_size		= sizeof(struct nl_seq_iter),
+	.ctx_arg_info_size	= 1,
+	.ctx_arg_info		= {
+		{ offsetof(struct bpf_iter__netlink, sk),
+		  PTR_TO_BTF_ID_OR_NULL },
+	},
+};
+
 static int __init bpf_iter_register(void)
 {
-	struct bpf_iter_reg reg_info = {
-		.target			= "netlink",
-		.seq_ops		= &netlink_seq_ops,
-		.init_seq_private	= bpf_iter_init_seq_net,
-		.fini_seq_private	= bpf_iter_fini_seq_net,
-		.seq_priv_size		= sizeof(struct nl_seq_iter),
-	};
-
-	return bpf_iter_reg_target(&reg_info);
+	return bpf_iter_reg_target(&netlink_reg_info);
 }
 #endif
 
diff --git a/samples/bpf/offwaketime_kern.c b/samples/bpf/offwaketime_kern.c
index c4ec10dbfc3b..d459f73412a4 100644
--- a/samples/bpf/offwaketime_kern.c
+++ b/samples/bpf/offwaketime_kern.c
@@ -5,12 +5,12 @@
  * License as published by the Free Software Foundation.
  */
 #include <uapi/linux/bpf.h>
-#include <bpf/bpf_helpers.h>
-#include <bpf/bpf_tracing.h>
 #include <uapi/linux/ptrace.h>
 #include <uapi/linux/perf_event.h>
 #include <linux/version.h>
 #include <linux/sched.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
 
 #define _(P) ({typeof(P) val; bpf_probe_read(&val, sizeof(val), &P); val;})
 
diff --git a/samples/bpf/sockex2_kern.c b/samples/bpf/sockex2_kern.c
index a41dd520bc53..b7997541f7ee 100644
--- a/samples/bpf/sockex2_kern.c
+++ b/samples/bpf/sockex2_kern.c
@@ -1,12 +1,12 @@
 #include <uapi/linux/bpf.h>
-#include <bpf/bpf_helpers.h>
-#include "bpf_legacy.h"
 #include <uapi/linux/in.h>
 #include <uapi/linux/if.h>
 #include <uapi/linux/if_ether.h>
 #include <uapi/linux/ip.h>
 #include <uapi/linux/ipv6.h>
 #include <uapi/linux/if_tunnel.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_legacy.h"
 #define IP_MF		0x2000
 #define IP_OFFSET	0x1FFF
 
diff --git a/samples/bpf/sockex3_kern.c b/samples/bpf/sockex3_kern.c
index 36d4dac23549..779a5249c418 100644
--- a/samples/bpf/sockex3_kern.c
+++ b/samples/bpf/sockex3_kern.c
@@ -5,8 +5,6 @@
  * License as published by the Free Software Foundation.
  */
 #include <uapi/linux/bpf.h>
-#include <bpf/bpf_helpers.h>
-#include "bpf_legacy.h"
 #include <uapi/linux/in.h>
 #include <uapi/linux/if.h>
 #include <uapi/linux/if_ether.h>
@@ -14,6 +12,8 @@
 #include <uapi/linux/ipv6.h>
 #include <uapi/linux/if_tunnel.h>
 #include <uapi/linux/mpls.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_legacy.h"
 #define IP_MF		0x2000
 #define IP_OFFSET	0x1FFF
 
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index fd882616ab52..292257995487 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -6919,7 +6919,7 @@ invalid_prog:
 
 #define BTF_TRACE_PREFIX "btf_trace_"
 #define BTF_LSM_PREFIX "bpf_lsm_"
-#define BTF_ITER_PREFIX "__bpf_iter__"
+#define BTF_ITER_PREFIX "bpf_iter_"
 #define BTF_MAX_NAME_SIZE 128
 
 static int find_btf_by_prefix_kind(const struct btf *btf, const char *prefix,
diff --git a/tools/testing/selftests/bpf/README.rst b/tools/testing/selftests/bpf/README.rst
new file mode 100644
index 000000000000..0f67f1b470b0
--- /dev/null
+++ b/tools/testing/selftests/bpf/README.rst
@@ -0,0 +1,43 @@
+==================
+BPF Selftest Notes
+==================
+
+Additional information about selftest failures are
+documented here.
+
+bpf_iter test failures with clang/llvm 10.0.0
+=============================================
+
+With clang/llvm 10.0.0, the following two bpf_iter tests failed:
+  * ``bpf_iter/ipv6_route``
+  * ``bpf_iter/netlink``
+
+The symptom for ``bpf_iter/ipv6_route`` looks like
+
+.. code-block:: c
+
+  2: (79) r8 = *(u64 *)(r1 +8)
+  ...
+  14: (bf) r2 = r8
+  15: (0f) r2 += r1
+  ; BPF_SEQ_PRINTF(seq, "%pi6 %02x ", &rt->fib6_dst.addr, rt->fib6_dst.plen);
+  16: (7b) *(u64 *)(r8 +64) = r2
+  only read is supported
+
+The symptom for ``bpf_iter/netlink`` looks like
+
+.. code-block:: c
+
+  ; struct netlink_sock *nlk = ctx->sk;
+  2: (79) r7 = *(u64 *)(r1 +8)
+  ...
+  15: (bf) r2 = r7
+  16: (0f) r2 += r1
+  ; BPF_SEQ_PRINTF(seq, "%pK %-3d ", s, s->sk_protocol);
+  17: (7b) *(u64 *)(r7 +0) = r2
+  only read is supported
+
+This is due to a llvm BPF backend bug. The fix 
+  https://reviews.llvm.org/D78466
+has been pushed to llvm 10.x release branch and will be
+available in 10.0.1. The fix is available in llvm 11.0.0 trunk.