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, 311 insertions, 0 deletions

diff --git a/net/mctp/test/utils.c b/net/mctp/test/utils.c
new file mode 100644
index 000000000..6eef8d485
--- /dev/null
+++ b/net/mctp/test/utils.c
@@ -0,0 +1,311 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/netdevice.h>
+#include <linux/mctp.h>
+#include <linux/if_arp.h>
+
+#include <net/mctp.h>
+#include <net/mctpdevice.h>
+#include <net/pkt_sched.h>
+
+#include "utils.h"
+
+static netdev_tx_t mctp_test_dev_tx(struct sk_buff *skb,
+				    struct net_device *ndev)
+{
+	struct mctp_test_dev *dev = netdev_priv(ndev);
+
+	skb_queue_tail(&dev->pkts, skb);
+
+	return NETDEV_TX_OK;
+}
+
+static const struct net_device_ops mctp_test_netdev_ops = {
+	.ndo_start_xmit = mctp_test_dev_tx,
+};
+
+static void mctp_test_dev_setup(struct net_device *ndev)
+{
+	ndev->type = ARPHRD_MCTP;
+	ndev->mtu = MCTP_DEV_TEST_MTU;
+	ndev->hard_header_len = 0;
+	ndev->tx_queue_len = 0;
+	ndev->flags = IFF_NOARP;
+	ndev->netdev_ops = &mctp_test_netdev_ops;
+	ndev->needs_free_netdev = true;
+}
+
+static struct mctp_test_dev *__mctp_test_create_dev(unsigned short lladdr_len,
+						    const unsigned char *lladdr)
+{
+	struct mctp_test_dev *dev;
+	struct net_device *ndev;
+	int rc;
+
+	if (WARN_ON(lladdr_len > MAX_ADDR_LEN))
+		return NULL;
+
+	ndev = alloc_netdev(sizeof(*dev), "mctptest%d", NET_NAME_ENUM,
+			    mctp_test_dev_setup);
+	if (!ndev)
+		return NULL;
+
+	dev = netdev_priv(ndev);
+	dev->ndev = ndev;
+	ndev->addr_len = lladdr_len;
+	dev_addr_set(ndev, lladdr);
+	skb_queue_head_init(&dev->pkts);
+
+	rc = register_netdev(ndev);
+	if (rc) {
+		free_netdev(ndev);
+		return NULL;
+	}
+
+	rcu_read_lock();
+	dev->mdev = __mctp_dev_get(ndev);
+	dev->mdev->net = mctp_default_net(dev_net(ndev));
+	rcu_read_unlock();
+
+	/* bring the device up; we want to be able to TX immediately */
+	rtnl_lock();
+	dev_open(ndev, NULL);
+	rtnl_unlock();
+
+	return dev;
+}
+
+struct mctp_test_dev *mctp_test_create_dev(void)
+{
+	return __mctp_test_create_dev(0, NULL);
+}
+
+struct mctp_test_dev *mctp_test_create_dev_with_addr(mctp_eid_t addr)
+{
+	struct mctp_test_dev *dev;
+
+	dev = __mctp_test_create_dev(0, NULL);
+	if (!dev)
+		return NULL;
+
+	dev->mdev->addrs = kmalloc_objs(u8, 1, GFP_KERNEL);
+	if (!dev->mdev->addrs) {
+		mctp_test_destroy_dev(dev);
+		return NULL;
+	}
+
+	dev->mdev->num_addrs = 1;
+	dev->mdev->addrs[0] = addr;
+
+	return dev;
+}
+
+struct mctp_test_dev *mctp_test_create_dev_lladdr(unsigned short lladdr_len,
+						  const unsigned char *lladdr)
+{
+	return __mctp_test_create_dev(lladdr_len, lladdr);
+}
+
+void mctp_test_destroy_dev(struct mctp_test_dev *dev)
+{
+	skb_queue_purge(&dev->pkts);
+	mctp_dev_put(dev->mdev);
+	unregister_netdev(dev->ndev);
+}
+
+static int mctp_test_dst_output(struct mctp_dst *dst, struct sk_buff *skb)
+{
+	skb->dev = dst->dev->dev;
+	dev_direct_xmit(skb, 0);
+
+	return 0;
+}
+
+/* local version of mctp_route_alloc() */
+static struct mctp_test_route *mctp_route_test_alloc(void)
+{
+	struct mctp_test_route *rt;
+
+	rt = kzalloc_obj(*rt);
+	if (!rt)
+		return NULL;
+
+	INIT_LIST_HEAD(&rt->rt.list);
+	refcount_set(&rt->rt.refs, 1);
+	rt->rt.output = mctp_test_dst_output;
+
+	return rt;
+}
+
+struct mctp_test_route *mctp_test_create_route_direct(struct net *net,
+						      struct mctp_dev *dev,
+						      mctp_eid_t eid,
+						      unsigned int mtu)
+{
+	struct mctp_test_route *rt;
+
+	rt = mctp_route_test_alloc();
+	if (!rt)
+		return NULL;
+
+	rt->rt.min = eid;
+	rt->rt.max = eid;
+	rt->rt.mtu = mtu;
+	rt->rt.type = RTN_UNSPEC;
+	rt->rt.dst_type = MCTP_ROUTE_DIRECT;
+	if (dev)
+		mctp_dev_hold(dev);
+	rt->rt.dev = dev;
+
+	list_add_rcu(&rt->rt.list, &net->mctp.routes);
+
+	return rt;
+}
+
+struct mctp_test_route *mctp_test_create_route_gw(struct net *net,
+						  unsigned int netid,
+						  mctp_eid_t eid,
+						  mctp_eid_t gw,
+						  unsigned int mtu)
+{
+	struct mctp_test_route *rt;
+
+	rt = mctp_route_test_alloc();
+	if (!rt)
+		return NULL;
+
+	rt->rt.min = eid;
+	rt->rt.max = eid;
+	rt->rt.mtu = mtu;
+	rt->rt.type = RTN_UNSPEC;
+	rt->rt.dst_type = MCTP_ROUTE_GATEWAY;
+	rt->rt.gateway.eid = gw;
+	rt->rt.gateway.net = netid;
+
+	list_add_rcu(&rt->rt.list, &net->mctp.routes);
+
+	return rt;
+}
+
+/* Convenience function for our test dst; release with mctp_dst_release() */
+void mctp_test_dst_setup(struct kunit *test, struct mctp_dst *dst,
+			 struct mctp_test_dev *dev, unsigned int mtu)
+{
+	unsigned long flags;
+
+	KUNIT_EXPECT_NOT_ERR_OR_NULL(test, dev);
+
+	memset(dst, 0, sizeof(*dst));
+
+	dst->dev = dev->mdev;
+	__mctp_dev_get(dst->dev->dev);
+	dst->mtu = mtu;
+	dst->output = mctp_test_dst_output;
+	dst->saddr = MCTP_ADDR_NULL;
+	spin_lock_irqsave(&dev->mdev->addrs_lock, flags);
+	if (dev->mdev->num_addrs)
+		dst->saddr = dev->mdev->addrs[0];
+	spin_unlock_irqrestore(&dev->mdev->addrs_lock, flags);
+}
+
+void mctp_test_route_destroy(struct kunit *test, struct mctp_test_route *rt)
+{
+	unsigned int refs;
+
+	rtnl_lock();
+	list_del_rcu(&rt->rt.list);
+	rtnl_unlock();
+
+	if (rt->rt.dst_type == MCTP_ROUTE_DIRECT && rt->rt.dev)
+		mctp_dev_put(rt->rt.dev);
+
+	refs = refcount_read(&rt->rt.refs);
+	KUNIT_ASSERT_EQ_MSG(test, refs, 1, "route ref imbalance");
+
+	kfree_rcu(&rt->rt, rcu);
+}
+
+void mctp_test_skb_set_dev(struct sk_buff *skb, struct mctp_test_dev *dev)
+{
+	struct mctp_skb_cb *cb;
+
+	cb = mctp_cb(skb);
+	cb->net = READ_ONCE(dev->mdev->net);
+	skb->dev = dev->ndev;
+}
+
+struct sk_buff *mctp_test_create_skb(const struct mctp_hdr *hdr,
+				     unsigned int data_len)
+{
+	size_t hdr_len = sizeof(*hdr);
+	struct sk_buff *skb;
+	unsigned int i;
+	u8 *buf;
+
+	skb = alloc_skb(hdr_len + data_len, GFP_KERNEL);
+	if (!skb)
+		return NULL;
+
+	__mctp_cb(skb);
+	memcpy(skb_put(skb, hdr_len), hdr, hdr_len);
+
+	buf = skb_put(skb, data_len);
+	for (i = 0; i < data_len; i++)
+		buf[i] = i & 0xff;
+
+	return skb;
+}
+
+struct sk_buff *__mctp_test_create_skb_data(const struct mctp_hdr *hdr,
+					    const void *data, size_t data_len)
+{
+	size_t hdr_len = sizeof(*hdr);
+	struct sk_buff *skb;
+
+	skb = alloc_skb(hdr_len + data_len, GFP_KERNEL);
+	if (!skb)
+		return NULL;
+
+	__mctp_cb(skb);
+	memcpy(skb_put(skb, hdr_len), hdr, hdr_len);
+	memcpy(skb_put(skb, data_len), data, data_len);
+
+	return skb;
+}
+
+void mctp_test_bind_run(struct kunit *test,
+			const struct mctp_test_bind_setup *setup,
+			int *ret_bind_errno, struct socket **sock)
+{
+	struct sockaddr_mctp addr;
+	int rc;
+
+	*ret_bind_errno = -EIO;
+
+	rc = sock_create_kern(&init_net, AF_MCTP, SOCK_DGRAM, 0, sock);
+	KUNIT_ASSERT_EQ(test, rc, 0);
+
+	/* connect() if requested */
+	if (setup->have_peer) {
+		memset(&addr, 0x0, sizeof(addr));
+		addr.smctp_family = AF_MCTP;
+		addr.smctp_network = setup->peer_net;
+		addr.smctp_addr.s_addr = setup->peer_addr;
+		/* connect() type must match bind() type */
+		addr.smctp_type = setup->bind_type;
+		rc = kernel_connect(*sock, (struct sockaddr_unsized *)&addr,
+				    sizeof(addr), 0);
+		KUNIT_EXPECT_EQ(test, rc, 0);
+	}
+
+	/* bind() */
+	memset(&addr, 0x0, sizeof(addr));
+	addr.smctp_family = AF_MCTP;
+	addr.smctp_network = setup->bind_net;
+	addr.smctp_addr.s_addr = setup->bind_addr;
+	addr.smctp_type = setup->bind_type;
+
+	*ret_bind_errno =
+		kernel_bind(*sock, (struct sockaddr_unsized *)&addr,
+			    sizeof(addr));
+}