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, 187 insertions, 0 deletions

diff --git a/include/trace/events/bridge.h b/include/trace/events/bridge.h
new file mode 100644
index 000000000..3fe4725c8
--- /dev/null
+++ b/include/trace/events/bridge.h
@@ -0,0 +1,187 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM bridge
+
+#if !defined(_TRACE_BRIDGE_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_BRIDGE_H
+
+#include <linux/netdevice.h>
+#include <linux/tracepoint.h>
+
+#include "../../../net/bridge/br_private.h"
+
+TRACE_EVENT(br_fdb_add,
+
+	TP_PROTO(struct ndmsg *ndm, struct net_device *dev,
+		 const unsigned char *addr, u16 vid, u16 nlh_flags),
+
+	TP_ARGS(ndm, dev, addr, vid, nlh_flags),
+
+	TP_STRUCT__entry(
+		__field(u8, ndm_flags)
+		__string(dev, dev->name)
+		__array(unsigned char, addr, ETH_ALEN)
+		__field(u16, vid)
+		__field(u16, nlh_flags)
+	),
+
+	TP_fast_assign(
+		__assign_str(dev);
+		memcpy(__entry->addr, addr, ETH_ALEN);
+		__entry->vid = vid;
+		__entry->nlh_flags = nlh_flags;
+		__entry->ndm_flags = ndm->ndm_flags;
+	),
+
+	TP_printk("dev %s addr %02x:%02x:%02x:%02x:%02x:%02x vid %u nlh_flags %04x ndm_flags %02x",
+		  __get_str(dev), __entry->addr[0], __entry->addr[1],
+		  __entry->addr[2], __entry->addr[3], __entry->addr[4],
+		  __entry->addr[5], __entry->vid,
+		  __entry->nlh_flags, __entry->ndm_flags)
+);
+
+TRACE_EVENT(br_fdb_external_learn_add,
+
+	TP_PROTO(struct net_bridge *br, struct net_bridge_port *p,
+		 const unsigned char *addr, u16 vid),
+
+	TP_ARGS(br, p, addr, vid),
+
+	TP_STRUCT__entry(
+		__string(br_dev, br->dev->name)
+		__string(dev, p ? p->dev->name : "null")
+		__array(unsigned char, addr, ETH_ALEN)
+		__field(u16, vid)
+	),
+
+	TP_fast_assign(
+		__assign_str(br_dev);
+		__assign_str(dev);
+		memcpy(__entry->addr, addr, ETH_ALEN);
+		__entry->vid = vid;
+	),
+
+	TP_printk("br_dev %s port %s addr %02x:%02x:%02x:%02x:%02x:%02x vid %u",
+		  __get_str(br_dev), __get_str(dev), __entry->addr[0],
+		  __entry->addr[1], __entry->addr[2], __entry->addr[3],
+		  __entry->addr[4], __entry->addr[5], __entry->vid)
+);
+
+TRACE_EVENT(fdb_delete,
+
+	TP_PROTO(struct net_bridge *br, struct net_bridge_fdb_entry *f),
+
+	TP_ARGS(br, f),
+
+	TP_STRUCT__entry(
+		__string(br_dev, br->dev->name)
+		__string(dev, f->dst ? f->dst->dev->name : "null")
+		__array(unsigned char, addr, ETH_ALEN)
+		__field(u16, vid)
+	),
+
+	TP_fast_assign(
+		__assign_str(br_dev);
+		__assign_str(dev);
+		memcpy(__entry->addr, f->key.addr.addr, ETH_ALEN);
+		__entry->vid = f->key.vlan_id;
+	),
+
+	TP_printk("br_dev %s dev %s addr %02x:%02x:%02x:%02x:%02x:%02x vid %u",
+		  __get_str(br_dev), __get_str(dev), __entry->addr[0],
+		  __entry->addr[1], __entry->addr[2], __entry->addr[3],
+		  __entry->addr[4], __entry->addr[5], __entry->vid)
+);
+
+TRACE_EVENT(br_fdb_update,
+
+	TP_PROTO(struct net_bridge *br, struct net_bridge_port *source,
+		 const unsigned char *addr, u16 vid, unsigned long flags),
+
+	TP_ARGS(br, source, addr, vid, flags),
+
+	TP_STRUCT__entry(
+		__string(br_dev, br->dev->name)
+		__string(dev, source->dev->name)
+		__array(unsigned char, addr, ETH_ALEN)
+		__field(u16, vid)
+		__field(unsigned long, flags)
+	),
+
+	TP_fast_assign(
+		__assign_str(br_dev);
+		__assign_str(dev);
+		memcpy(__entry->addr, addr, ETH_ALEN);
+		__entry->vid = vid;
+		__entry->flags = flags;
+	),
+
+	TP_printk("br_dev %s source %s addr %02x:%02x:%02x:%02x:%02x:%02x vid %u flags 0x%lx",
+		  __get_str(br_dev), __get_str(dev), __entry->addr[0],
+		  __entry->addr[1], __entry->addr[2], __entry->addr[3],
+		  __entry->addr[4], __entry->addr[5], __entry->vid,
+		  __entry->flags)
+);
+
+TRACE_EVENT(br_mdb_full,
+
+	TP_PROTO(const struct net_device *dev,
+		 const struct br_ip *group),
+
+	TP_ARGS(dev, group),
+
+	TP_STRUCT__entry(
+		__string(dev, dev->name)
+		__field(int, af)
+		__field(u16, vid)
+		__array(__u8, src, 16)
+		__array(__u8, grp, 16)
+		__array(__u8, grpmac, ETH_ALEN) /* For af == 0. */
+	),
+
+	TP_fast_assign(
+		struct in6_addr *in6;
+
+		__assign_str(dev);
+		__entry->vid = group->vid;
+
+		if (!group->proto) {
+			__entry->af = 0;
+
+			memset(__entry->src, 0, sizeof(__entry->src));
+			memset(__entry->grp, 0, sizeof(__entry->grp));
+			memcpy(__entry->grpmac, group->dst.mac_addr, ETH_ALEN);
+		} else if (group->proto == htons(ETH_P_IP)) {
+			__entry->af = AF_INET;
+
+			in6 = (struct in6_addr *)__entry->src;
+			ipv6_addr_set_v4mapped(group->src.ip4, in6);
+
+			in6 = (struct in6_addr *)__entry->grp;
+			ipv6_addr_set_v4mapped(group->dst.ip4, in6);
+
+			memset(__entry->grpmac, 0, ETH_ALEN);
+
+#if IS_ENABLED(CONFIG_IPV6)
+		} else {
+			__entry->af = AF_INET6;
+
+			in6 = (struct in6_addr *)__entry->src;
+			*in6 = group->src.ip6;
+
+			in6 = (struct in6_addr *)__entry->grp;
+			*in6 = group->dst.ip6;
+
+			memset(__entry->grpmac, 0, ETH_ALEN);
+#endif
+		}
+	),
+
+	TP_printk("dev %s af %u src %pI6c grp %pI6c/%pM vid %u",
+		  __get_str(dev), __entry->af, __entry->src, __entry->grp,
+		  __entry->grpmac, __entry->vid)
+);
+
+#endif /* _TRACE_BRIDGE_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>