kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 462 insertions, 0 deletions

diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
new file mode 100644
index 000000000..78f50c93c
--- /dev/null
+++ b/net/ipv6/ip6_offload.c
@@ -0,0 +1,462 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *	IPV6 GSO/GRO offload support
+ *	Linux INET6 implementation
+ */
+
+#include <linux/kernel.h>
+#include <linux/socket.h>
+#include <linux/netdevice.h>
+#include <linux/skbuff.h>
+#include <linux/printk.h>
+
+#include <net/protocol.h>
+#include <net/ipv6.h>
+#include <net/inet_common.h>
+#include <net/tcp.h>
+#include <net/udp.h>
+#include <net/gro.h>
+#include <net/gso.h>
+
+#include "ip6_offload.h"
+#include "tcpv6_offload.c"
+
+static int ipv6_gro_pull_exthdrs(struct sk_buff *skb, int off, int proto)
+{
+	const struct net_offload *ops = NULL;
+	struct ipv6_opt_hdr *opth;
+
+	for (;;) {
+		int len;
+
+		ops = rcu_dereference(inet6_offloads[proto]);
+
+		if (unlikely(!ops))
+			break;
+
+		if (!(ops->flags & INET6_PROTO_GSO_EXTHDR))
+			break;
+
+		opth = skb_gro_header(skb, off + sizeof(*opth), off);
+		if (unlikely(!opth))
+			break;
+
+		len = ipv6_optlen(opth);
+
+		opth = skb_gro_header(skb, off + len, off);
+		if (unlikely(!opth))
+			break;
+		proto = opth->nexthdr;
+
+		off += len;
+	}
+
+	skb_gro_pull(skb, off - skb_gro_receive_network_offset(skb));
+	return proto;
+}
+
+static int ipv6_gso_pull_exthdrs(struct sk_buff *skb, int proto)
+{
+	const struct net_offload *ops = NULL;
+
+	for (;;) {
+		struct ipv6_opt_hdr *opth;
+		int len;
+
+		ops = rcu_dereference(inet6_offloads[proto]);
+
+		if (unlikely(!ops))
+			break;
+
+		if (!(ops->flags & INET6_PROTO_GSO_EXTHDR))
+			break;
+
+		if (unlikely(!pskb_may_pull(skb, 8)))
+			break;
+
+		opth = (void *)skb->data;
+		len = ipv6_optlen(opth);
+
+		if (unlikely(!pskb_may_pull(skb, len)))
+			break;
+
+		opth = (void *)skb->data;
+		proto = opth->nexthdr;
+		__skb_pull(skb, len);
+	}
+
+	return proto;
+}
+
+static struct sk_buff *ipv6_gso_segment(struct sk_buff *skb,
+	netdev_features_t features)
+{
+	struct sk_buff *segs = ERR_PTR(-EINVAL);
+	struct ipv6hdr *ipv6h;
+	const struct net_offload *ops;
+	int proto;
+	struct frag_hdr *fptr;
+	unsigned int payload_len;
+	u8 *prevhdr;
+	int offset = 0;
+	bool encap, udpfrag;
+	int nhoff;
+	bool gso_partial;
+
+	skb_reset_network_header(skb);
+	nhoff = skb_network_header(skb) - skb_mac_header(skb);
+	if (unlikely(!pskb_may_pull(skb, sizeof(*ipv6h))))
+		goto out;
+
+	encap = SKB_GSO_CB(skb)->encap_level > 0;
+	if (encap)
+		features &= skb->dev->hw_enc_features;
+	SKB_GSO_CB(skb)->encap_level += sizeof(*ipv6h);
+
+	ipv6h = ipv6_hdr(skb);
+	__skb_pull(skb, sizeof(*ipv6h));
+	segs = ERR_PTR(-EPROTONOSUPPORT);
+
+	proto = ipv6_gso_pull_exthdrs(skb, ipv6h->nexthdr);
+
+	if (skb->encapsulation &&
+	    skb_shinfo(skb)->gso_type & (SKB_GSO_IPXIP4 | SKB_GSO_IPXIP6))
+		udpfrag = proto == IPPROTO_UDP && encap &&
+			  (skb_shinfo(skb)->gso_type & SKB_GSO_UDP);
+	else
+		udpfrag = proto == IPPROTO_UDP && !skb->encapsulation &&
+			  (skb_shinfo(skb)->gso_type & SKB_GSO_UDP);
+
+	ops = rcu_dereference(inet6_offloads[proto]);
+	if (likely(ops && ops->callbacks.gso_segment)) {
+		if (!skb_reset_transport_header_careful(skb))
+			goto out;
+
+		segs = ops->callbacks.gso_segment(skb, features);
+		if (!segs)
+			skb->network_header = skb_mac_header(skb) + nhoff - skb->head;
+	}
+
+	if (IS_ERR_OR_NULL(segs))
+		goto out;
+
+	gso_partial = !!(skb_shinfo(segs)->gso_type & SKB_GSO_PARTIAL);
+
+	for (skb = segs; skb; skb = skb->next) {
+		ipv6h = (struct ipv6hdr *)(skb_mac_header(skb) + nhoff);
+		if (gso_partial && skb_is_gso(skb))
+			payload_len = skb_shinfo(skb)->gso_size +
+				      SKB_GSO_CB(skb)->data_offset +
+				      skb->head - (unsigned char *)(ipv6h + 1);
+		else
+			payload_len = skb->len - nhoff - sizeof(*ipv6h);
+		ipv6h->payload_len = htons(payload_len);
+		skb->network_header = (u8 *)ipv6h - skb->head;
+		skb_reset_mac_len(skb);
+
+		if (udpfrag) {
+			int err = ip6_find_1stfragopt(skb, &prevhdr);
+			if (err < 0) {
+				kfree_skb_list(segs);
+				return ERR_PTR(err);
+			}
+			fptr = (struct frag_hdr *)((u8 *)ipv6h + err);
+			fptr->frag_off = htons(offset);
+			if (skb->next)
+				fptr->frag_off |= htons(IP6_MF);
+			offset += (ntohs(ipv6h->payload_len) -
+				   sizeof(struct frag_hdr));
+		}
+		if (encap)
+			skb_reset_inner_headers(skb);
+	}
+
+out:
+	return segs;
+}
+
+/* Return the total length of all the extension hdrs, following the same
+ * logic in ipv6_gso_pull_exthdrs() when parsing ext-hdrs.
+ */
+static int ipv6_exthdrs_len(struct ipv6hdr *iph,
+			    const struct net_offload **opps)
+{
+	struct ipv6_opt_hdr *opth = (void *)iph;
+	int len = 0, proto, optlen = sizeof(*iph);
+
+	proto = iph->nexthdr;
+	for (;;) {
+		*opps = rcu_dereference(inet6_offloads[proto]);
+		if (unlikely(!(*opps)))
+			break;
+		if (!((*opps)->flags & INET6_PROTO_GSO_EXTHDR))
+			break;
+
+		opth = (void *)opth + optlen;
+		optlen = ipv6_optlen(opth);
+		len += optlen;
+		proto = opth->nexthdr;
+	}
+	return len;
+}
+
+INDIRECT_CALLABLE_SCOPE struct sk_buff *ipv6_gro_receive(struct list_head *head,
+							 struct sk_buff *skb)
+{
+	const struct net_offload *ops;
+	struct sk_buff *pp = NULL;
+	struct sk_buff *p;
+	struct ipv6hdr *iph;
+	unsigned int nlen;
+	unsigned int hlen;
+	unsigned int off;
+	u16 flush = 1;
+	int proto;
+
+	off = skb_gro_offset(skb);
+	hlen = off + sizeof(*iph);
+	iph = skb_gro_header(skb, hlen, off);
+	if (unlikely(!iph))
+		goto out;
+
+	NAPI_GRO_CB(skb)->network_offsets[NAPI_GRO_CB(skb)->encap_mark] = off;
+
+	flush += ntohs(iph->payload_len) != skb->len - hlen;
+
+	proto = iph->nexthdr;
+	ops = rcu_dereference(inet6_offloads[proto]);
+	if (!ops || !ops->callbacks.gro_receive) {
+		proto = ipv6_gro_pull_exthdrs(skb, hlen, proto);
+
+		ops = rcu_dereference(inet6_offloads[proto]);
+		if (!ops || !ops->callbacks.gro_receive)
+			goto out;
+
+		iph = skb_gro_network_header(skb);
+	} else {
+		skb_gro_pull(skb, sizeof(*iph));
+	}
+
+	skb_set_transport_header(skb, skb_gro_offset(skb));
+
+	NAPI_GRO_CB(skb)->proto = proto;
+
+	flush--;
+	nlen = skb_gro_offset(skb) - off;
+
+	list_for_each_entry(p, head, list) {
+		const struct ipv6hdr *iph2;
+		__be32 first_word; /* <Version:4><Traffic_Class:8><Flow_Label:20> */
+
+		if (!NAPI_GRO_CB(p)->same_flow)
+			continue;
+
+		iph2 = (struct ipv6hdr *)(p->data + off);
+		first_word = *(__be32 *)iph ^ *(__be32 *)iph2;
+
+		/* All fields must match except length and Traffic Class.
+		 * XXX skbs on the gro_list have all been parsed and pulled
+		 * already so we don't need to compare nlen
+		 * (nlen != (sizeof(*iph2) + ipv6_exthdrs_len(iph2, &ops)))
+		 * memcmp() alone below is sufficient, right?
+		 */
+		 if ((first_word & htonl(0xF00FFFFF)) ||
+		     !ipv6_addr_equal(&iph->saddr, &iph2->saddr) ||
+		     !ipv6_addr_equal(&iph->daddr, &iph2->daddr) ||
+		     iph->nexthdr != iph2->nexthdr) {
+not_same_flow:
+			NAPI_GRO_CB(p)->same_flow = 0;
+			continue;
+		}
+		if (unlikely(nlen > sizeof(struct ipv6hdr))) {
+			if (memcmp(iph + 1, iph2 + 1,
+				   nlen - sizeof(struct ipv6hdr)))
+				goto not_same_flow;
+		}
+	}
+
+	NAPI_GRO_CB(skb)->flush |= flush;
+
+	skb_gro_postpull_rcsum(skb, iph, nlen);
+
+	if (unlikely(gro_recursion_inc_test(skb))) {
+		flush = 1;
+		goto out;
+	}
+
+	if (likely(proto == IPPROTO_TCP))
+		pp = tcp6_gro_receive(head, skb);
+#if IS_ENABLED(CONFIG_IPV6)
+	else if (likely(proto == IPPROTO_UDP))
+		pp = udp6_gro_receive(head, skb);
+#endif
+	else
+		pp = ops->callbacks.gro_receive(head, skb);
+out:
+	skb_gro_flush_final(skb, pp, flush);
+
+	return pp;
+}
+EXPORT_INDIRECT_CALLABLE(ipv6_gro_receive);
+
+static struct sk_buff *sit_ip6ip6_gro_receive(struct list_head *head,
+					      struct sk_buff *skb)
+{
+	/* Common GRO receive for SIT and IP6IP6 */
+
+	if (NAPI_GRO_CB(skb)->encap_mark) {
+		NAPI_GRO_CB(skb)->flush = 1;
+		return NULL;
+	}
+
+	NAPI_GRO_CB(skb)->encap_mark = 1;
+
+	return ipv6_gro_receive(head, skb);
+}
+
+static struct sk_buff *ip4ip6_gro_receive(struct list_head *head,
+					  struct sk_buff *skb)
+{
+	/* Common GRO receive for SIT and IP6IP6 */
+
+	if (NAPI_GRO_CB(skb)->encap_mark) {
+		NAPI_GRO_CB(skb)->flush = 1;
+		return NULL;
+	}
+
+	NAPI_GRO_CB(skb)->encap_mark = 1;
+
+	return inet_gro_receive(head, skb);
+}
+
+INDIRECT_CALLABLE_SCOPE int ipv6_gro_complete(struct sk_buff *skb, int nhoff)
+{
+	const struct net_offload *ops;
+	struct ipv6hdr *iph;
+	int err = -ENOSYS;
+
+	if (skb->encapsulation) {
+		skb_set_inner_protocol(skb, cpu_to_be16(ETH_P_IPV6));
+		skb_set_inner_network_header(skb, nhoff);
+	}
+
+	iph = (struct ipv6hdr *)(skb->data + nhoff);
+	ipv6_set_payload_len(iph, skb->len - nhoff - sizeof(*iph));
+
+	nhoff += sizeof(*iph) + ipv6_exthdrs_len(iph, &ops);
+
+	if (likely(ops == &net_hotdata.tcpv6_offload))
+		return tcp6_gro_complete(skb, nhoff);
+#if IS_ENABLED(CONFIG_IPV6)
+	if (ops == &net_hotdata.udpv6_offload)
+		return udp6_gro_complete(skb, nhoff);
+#endif
+
+	if (WARN_ON(!ops || !ops->callbacks.gro_complete))
+		goto out;
+
+	err = ops->callbacks.gro_complete(skb, nhoff);
+
+out:
+	return err;
+}
+EXPORT_INDIRECT_CALLABLE(ipv6_gro_complete);
+
+static int sit_gro_complete(struct sk_buff *skb, int nhoff)
+{
+	skb->encapsulation = 1;
+	skb_shinfo(skb)->gso_type |= SKB_GSO_IPXIP4;
+	return ipv6_gro_complete(skb, nhoff);
+}
+
+static int ip6ip6_gro_complete(struct sk_buff *skb, int nhoff)
+{
+	skb->encapsulation = 1;
+	skb_shinfo(skb)->gso_type |= SKB_GSO_IPXIP6;
+	return ipv6_gro_complete(skb, nhoff);
+}
+
+static int ip4ip6_gro_complete(struct sk_buff *skb, int nhoff)
+{
+	skb->encapsulation = 1;
+	skb_shinfo(skb)->gso_type |= SKB_GSO_IPXIP6;
+	return inet_gro_complete(skb, nhoff);
+}
+
+
+static struct sk_buff *sit_gso_segment(struct sk_buff *skb,
+				       netdev_features_t features)
+{
+	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_IPXIP4))
+		return ERR_PTR(-EINVAL);
+
+	return ipv6_gso_segment(skb, features);
+}
+
+static struct sk_buff *ip4ip6_gso_segment(struct sk_buff *skb,
+					  netdev_features_t features)
+{
+	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_IPXIP6))
+		return ERR_PTR(-EINVAL);
+
+	return inet_gso_segment(skb, features);
+}
+
+static struct sk_buff *ip6ip6_gso_segment(struct sk_buff *skb,
+					  netdev_features_t features)
+{
+	if (!(skb_shinfo(skb)->gso_type & SKB_GSO_IPXIP6))
+		return ERR_PTR(-EINVAL);
+
+	return ipv6_gso_segment(skb, features);
+}
+
+static const struct net_offload sit_offload = {
+	.callbacks = {
+		.gso_segment	= sit_gso_segment,
+		.gro_receive    = sit_ip6ip6_gro_receive,
+		.gro_complete   = sit_gro_complete,
+	},
+};
+
+static const struct net_offload ip4ip6_offload = {
+	.callbacks = {
+		.gso_segment	= ip4ip6_gso_segment,
+		.gro_receive    = ip4ip6_gro_receive,
+		.gro_complete   = ip4ip6_gro_complete,
+	},
+};
+
+static const struct net_offload ip6ip6_offload = {
+	.callbacks = {
+		.gso_segment	= ip6ip6_gso_segment,
+		.gro_receive    = sit_ip6ip6_gro_receive,
+		.gro_complete   = ip6ip6_gro_complete,
+	},
+};
+static int __init ipv6_offload_init(void)
+{
+
+	if (tcpv6_offload_init() < 0)
+		pr_crit("%s: Cannot add TCP protocol offload\n", __func__);
+	if (ipv6_exthdrs_offload_init() < 0)
+		pr_crit("%s: Cannot add EXTHDRS protocol offload\n", __func__);
+
+	net_hotdata.ipv6_packet_offload = (struct packet_offload) {
+		.type = cpu_to_be16(ETH_P_IPV6),
+		.callbacks = {
+			.gso_segment = ipv6_gso_segment,
+			.gro_receive = ipv6_gro_receive,
+			.gro_complete = ipv6_gro_complete,
+		},
+	};
+	dev_add_offload(&net_hotdata.ipv6_packet_offload);
+
+	inet_add_offload(&sit_offload, IPPROTO_IPV6);
+	inet6_add_offload(&ip6ip6_offload, IPPROTO_IPV6);
+	inet6_add_offload(&ip4ip6_offload, IPPROTO_IPIP);
+
+	return 0;
+}
+
+fs_initcall(ipv6_offload_init);