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, 215 insertions, 0 deletions

diff --git a/net/mpls/internal.h b/net/mpls/internal.h
new file mode 100644
index 000000000..80cb5bbcd
--- /dev/null
+++ b/net/mpls/internal.h
@@ -0,0 +1,215 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef MPLS_INTERNAL_H
+#define MPLS_INTERNAL_H
+#include <net/mpls.h>
+
+/* put a reasonable limit on the number of labels
+ * we will accept from userspace
+ */
+#define MAX_NEW_LABELS 30
+
+struct mpls_entry_decoded {
+	u32 label;
+	u8 ttl;
+	u8 tc;
+	u8 bos;
+};
+
+struct mpls_pcpu_stats {
+	struct mpls_link_stats	stats;
+	struct u64_stats_sync	syncp;
+};
+
+struct mpls_dev {
+	int				input_enabled;
+	struct net_device		*dev;
+	struct mpls_pcpu_stats __percpu	*stats;
+
+	struct ctl_table_header		*sysctl;
+	struct rcu_head			rcu;
+};
+
+#if BITS_PER_LONG == 32
+
+#define MPLS_INC_STATS_LEN(mdev, len, pkts_field, bytes_field)		\
+	do {								\
+		TYPEOF_UNQUAL(*(mdev)->stats) *ptr =			\
+			raw_cpu_ptr((mdev)->stats);			\
+		local_bh_disable();					\
+		u64_stats_update_begin(&ptr->syncp);			\
+		ptr->stats.pkts_field++;				\
+		ptr->stats.bytes_field += (len);			\
+		u64_stats_update_end(&ptr->syncp);			\
+		local_bh_enable();					\
+	} while (0)
+
+#define MPLS_INC_STATS(mdev, field)					\
+	do {								\
+		TYPEOF_UNQUAL(*(mdev)->stats) *ptr =			\
+			raw_cpu_ptr((mdev)->stats);			\
+		local_bh_disable();					\
+		u64_stats_update_begin(&ptr->syncp);			\
+		ptr->stats.field++;					\
+		u64_stats_update_end(&ptr->syncp);			\
+		local_bh_enable();					\
+	} while (0)
+
+#else
+
+#define MPLS_INC_STATS_LEN(mdev, len, pkts_field, bytes_field)		\
+	do {								\
+		this_cpu_inc((mdev)->stats->stats.pkts_field);		\
+		this_cpu_add((mdev)->stats->stats.bytes_field, (len));	\
+	} while (0)
+
+#define MPLS_INC_STATS(mdev, field)			\
+	this_cpu_inc((mdev)->stats->stats.field)
+
+#endif
+
+struct sk_buff;
+
+#define LABEL_NOT_SPECIFIED (1 << 20)
+
+/* This maximum ha length copied from the definition of struct neighbour */
+#define VIA_ALEN_ALIGN sizeof(unsigned long)
+#define MAX_VIA_ALEN (ALIGN(MAX_ADDR_LEN, VIA_ALEN_ALIGN))
+
+enum mpls_payload_type {
+	MPT_UNSPEC, /* IPv4 or IPv6 */
+	MPT_IPV4 = 4,
+	MPT_IPV6 = 6,
+
+	/* Other types not implemented:
+	 *  - Pseudo-wire with or without control word (RFC4385)
+	 *  - GAL (RFC5586)
+	 */
+};
+
+struct mpls_nh { /* next hop label forwarding entry */
+	struct net_device	*nh_dev;
+	netdevice_tracker	nh_dev_tracker;
+
+	/* nh_flags is accessed under RCU in the packet path; it is
+	 * modified handling netdev events with rtnl lock held
+	 */
+	unsigned int		nh_flags;
+	u8			nh_labels;
+	u8			nh_via_alen;
+	u8			nh_via_table;
+	u8			nh_reserved1;
+
+	u32			nh_label[];
+};
+
+/* offset of via from beginning of mpls_nh */
+#define MPLS_NH_VIA_OFF(num_labels) \
+		ALIGN(sizeof(struct mpls_nh) + (num_labels) * sizeof(u32), \
+		      VIA_ALEN_ALIGN)
+
+/* all nexthops within a route have the same size based on the
+ * max number of labels and max via length across all nexthops
+ */
+#define MPLS_NH_SIZE(num_labels, max_via_alen)		\
+		(MPLS_NH_VIA_OFF((num_labels)) +	\
+		ALIGN((max_via_alen), VIA_ALEN_ALIGN))
+
+enum mpls_ttl_propagation {
+	MPLS_TTL_PROP_DEFAULT,
+	MPLS_TTL_PROP_ENABLED,
+	MPLS_TTL_PROP_DISABLED,
+};
+
+/* The route, nexthops and vias are stored together in the same memory
+ * block:
+ *
+ * +----------------------+
+ * | mpls_route           |
+ * +----------------------+
+ * | mpls_nh 0            |
+ * +----------------------+
+ * | alignment padding    |   4 bytes for odd number of labels
+ * +----------------------+
+ * | via[rt_max_alen] 0   |
+ * +----------------------+
+ * | alignment padding    |   via's aligned on sizeof(unsigned long)
+ * +----------------------+
+ * | ...                  |
+ * +----------------------+
+ * | mpls_nh n-1          |
+ * +----------------------+
+ * | via[rt_max_alen] n-1 |
+ * +----------------------+
+ */
+struct mpls_route { /* next hop label forwarding entry */
+	struct rcu_head		rt_rcu;
+	u8			rt_protocol;
+	u8			rt_payload_type;
+	u8			rt_max_alen;
+	u8			rt_ttl_propagate;
+	u8			rt_nhn;
+	/* rt_nhn_alive is accessed under RCU in the packet path; it
+	 * is modified handling netdev events with rtnl lock held
+	 */
+	u8			rt_nhn_alive;
+	u8			rt_nh_size;
+	u8			rt_via_offset;
+	u8			rt_reserved1;
+	struct mpls_nh		rt_nh[];
+};
+
+#define for_nexthops(rt) {						\
+	int nhsel; const struct mpls_nh *nh;				\
+	for (nhsel = 0, nh = (rt)->rt_nh;				\
+	     nhsel < (rt)->rt_nhn;					\
+	     nh = (void *)nh + (rt)->rt_nh_size, nhsel++)
+
+#define change_nexthops(rt) {						\
+	int nhsel; struct mpls_nh *nh;					\
+	for (nhsel = 0, nh = (rt)->rt_nh;				\
+	     nhsel < (rt)->rt_nhn;					\
+	     nh = (void *)nh + (rt)->rt_nh_size, nhsel++)
+
+#define endfor_nexthops(rt) }
+
+static inline struct mpls_entry_decoded mpls_entry_decode(struct mpls_shim_hdr *hdr)
+{
+	struct mpls_entry_decoded result;
+	unsigned entry = be32_to_cpu(hdr->label_stack_entry);
+
+	result.label = (entry & MPLS_LS_LABEL_MASK) >> MPLS_LS_LABEL_SHIFT;
+	result.ttl = (entry & MPLS_LS_TTL_MASK) >> MPLS_LS_TTL_SHIFT;
+	result.tc =  (entry & MPLS_LS_TC_MASK) >> MPLS_LS_TC_SHIFT;
+	result.bos = (entry & MPLS_LS_S_MASK) >> MPLS_LS_S_SHIFT;
+
+	return result;
+}
+
+#define mpls_dereference(net, p)					\
+	rcu_dereference_protected(					\
+		(p),							\
+		lockdep_is_held(&(net)->mpls.platform_mutex))
+
+static inline struct mpls_dev *mpls_dev_rcu(const struct net_device *dev)
+{
+	return rcu_dereference(dev->mpls_ptr);
+}
+
+static inline struct mpls_dev *mpls_dev_get(const struct net *net,
+					    const struct net_device *dev)
+{
+	return mpls_dereference(net, dev->mpls_ptr);
+}
+
+int nla_put_labels(struct sk_buff *skb, int attrtype,  u8 labels,
+		   const u32 label[]);
+int nla_get_labels(const struct nlattr *nla, u8 max_labels, u8 *labels,
+		   u32 label[], struct netlink_ext_ack *extack);
+bool mpls_output_possible(const struct net_device *dev);
+unsigned int mpls_dev_mtu(const struct net_device *dev);
+bool mpls_pkt_too_big(const struct sk_buff *skb, unsigned int mtu);
+void mpls_stats_inc_outucastpkts(struct net *net,
+				 struct net_device *dev,
+				 const struct sk_buff *skb);
+
+#endif /* MPLS_INTERNAL_H */