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, 255 insertions, 0 deletions

diff --git a/include/trace/events/neigh.h b/include/trace/events/neigh.h
new file mode 100644
index 000000000..12362c35d
--- /dev/null
+++ b/include/trace/events/neigh.h
@@ -0,0 +1,255 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM neigh
+
+#if !defined(_TRACE_NEIGH_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_NEIGH_H
+
+#include <linux/skbuff.h>
+#include <linux/netdevice.h>
+#include <linux/tracepoint.h>
+#include <net/neighbour.h>
+
+#define neigh_state_str(state)				\
+	__print_symbolic(state,				\
+		{ NUD_INCOMPLETE, "incomplete" },	\
+		{ NUD_REACHABLE, "reachable" },		\
+		{ NUD_STALE, "stale" },			\
+		{ NUD_DELAY, "delay" },			\
+		{ NUD_PROBE, "probe" },			\
+		{ NUD_FAILED, "failed" },		\
+		{ NUD_NOARP, "noarp" },			\
+		{ NUD_PERMANENT, "permanent"})
+
+TRACE_EVENT(neigh_create,
+
+	TP_PROTO(struct neigh_table *tbl, struct net_device *dev,
+		 const void *pkey, const struct neighbour *n,
+		 bool exempt_from_gc),
+
+	TP_ARGS(tbl, dev, pkey, n, exempt_from_gc),
+
+	TP_STRUCT__entry(
+		__field(u32, family)
+		__string(dev, dev ? dev->name : "NULL")
+		__field(int, entries)
+		__field(u8, created)
+		__field(u8, gc_exempt)
+		__array(u8, primary_key4, 4)
+		__array(u8, primary_key6, 16)
+	),
+
+	TP_fast_assign(
+		__be32 *p32;
+
+		__entry->family = tbl->family;
+		__assign_str(dev);
+		__entry->entries = atomic_read(&tbl->gc_entries);
+		__entry->created = n != NULL;
+		__entry->gc_exempt = exempt_from_gc;
+		p32 = (__be32 *)__entry->primary_key4;
+
+		if (tbl->family == AF_INET)
+			*p32 = *(__be32 *)pkey;
+		else
+			*p32 = 0;
+
+#if IS_ENABLED(CONFIG_IPV6)
+		if (tbl->family == AF_INET6) {
+			struct in6_addr *pin6;
+
+			pin6 = (struct in6_addr *)__entry->primary_key6;
+			*pin6 = *(struct in6_addr *)pkey;
+		}
+#endif
+	),
+
+	TP_printk("family %d dev %s entries %d primary_key4 %pI4 primary_key6 %pI6c created %d gc_exempt %d",
+		  __entry->family, __get_str(dev), __entry->entries,
+		  __entry->primary_key4, __entry->primary_key6,
+		  __entry->created, __entry->gc_exempt)
+);
+
+TRACE_EVENT(neigh_update,
+
+	TP_PROTO(struct neighbour *n, const u8 *lladdr, u8 new,
+		 u32 flags, u32 nlmsg_pid),
+
+	TP_ARGS(n, lladdr, new, flags, nlmsg_pid),
+
+	TP_STRUCT__entry(
+		__field(u32, family)
+		__string(dev, (n->dev ? n->dev->name : "NULL"))
+		__array(u8, lladdr, MAX_ADDR_LEN)
+		__field(u8, lladdr_len)
+		__field(u8, flags)
+		__field(u8, nud_state)
+		__field(u8, type)
+		__field(u8, dead)
+		__field(int, refcnt)
+		__array(__u8, primary_key4, 4)
+		__array(__u8, primary_key6, 16)
+		__field(unsigned long, confirmed)
+		__field(unsigned long, updated)
+		__field(unsigned long, used)
+		__array(u8, new_lladdr, MAX_ADDR_LEN)
+		__field(u8, new_state)
+		__field(u32, update_flags)
+		__field(u32, pid)
+	),
+
+	TP_fast_assign(
+		int lladdr_len = (n->dev ? n->dev->addr_len : MAX_ADDR_LEN);
+		struct in6_addr *pin6;
+		__be32 *p32;
+
+		__entry->family = n->tbl->family;
+		__assign_str(dev);
+		__entry->lladdr_len = lladdr_len;
+		memcpy(__entry->lladdr, n->ha, lladdr_len);
+		__entry->flags = n->flags;
+		__entry->nud_state = n->nud_state;
+		__entry->type = n->type;
+		__entry->dead = n->dead;
+		__entry->refcnt = refcount_read(&n->refcnt);
+		pin6 = (struct in6_addr *)__entry->primary_key6;
+		p32 = (__be32 *)__entry->primary_key4;
+
+		if (n->tbl->family == AF_INET)
+			*p32 = *(__be32 *)n->primary_key;
+		else
+			*p32 = 0;
+
+#if IS_ENABLED(CONFIG_IPV6)
+		if (n->tbl->family == AF_INET6) {
+			pin6 = (struct in6_addr *)__entry->primary_key6;
+			*pin6 = *(struct in6_addr *)n->primary_key;
+		} else
+#endif
+		{
+			ipv6_addr_set_v4mapped(*p32, pin6);
+		}
+		__entry->confirmed = n->confirmed;
+		__entry->updated = n->updated;
+		__entry->used = n->used;
+		if (lladdr)
+			memcpy(__entry->new_lladdr, lladdr, lladdr_len);
+		__entry->new_state = new;
+		__entry->update_flags = flags;
+		__entry->pid = nlmsg_pid;
+	),
+
+	TP_printk("family %d dev %s lladdr %s flags %02x nud_state %s type %02x "
+		  "dead %d refcnt %d primary_key4 %pI4 primary_key6 %pI6c "
+		  "confirmed %lu updated %lu used %lu new_lladdr %s "
+		  "new_state %s update_flags %02x pid %d",
+		  __entry->family, __get_str(dev),
+		  __print_hex_str(__entry->lladdr, __entry->lladdr_len),
+		  __entry->flags, neigh_state_str(__entry->nud_state),
+		  __entry->type, __entry->dead, __entry->refcnt,
+		  __entry->primary_key4, __entry->primary_key6,
+		  __entry->confirmed, __entry->updated, __entry->used,
+		  __print_hex_str(__entry->new_lladdr, __entry->lladdr_len),
+		  neigh_state_str(__entry->new_state),
+		  __entry->update_flags, __entry->pid)
+);
+
+DECLARE_EVENT_CLASS(neigh__update,
+	TP_PROTO(struct neighbour *n, int err),
+	TP_ARGS(n, err),
+	TP_STRUCT__entry(
+		__field(u32, family)
+		__string(dev, (n->dev ? n->dev->name : "NULL"))
+		__array(u8, lladdr, MAX_ADDR_LEN)
+		__field(u8, lladdr_len)
+		__field(u8, flags)
+		__field(u8, nud_state)
+		__field(u8, type)
+		__field(u8, dead)
+		__field(int, refcnt)
+		__array(__u8, primary_key4, 4)
+		__array(__u8, primary_key6, 16)
+		__field(unsigned long, confirmed)
+		__field(unsigned long, updated)
+		__field(unsigned long, used)
+		__field(u32, err)
+	),
+
+	TP_fast_assign(
+		int lladdr_len = (n->dev ? n->dev->addr_len : MAX_ADDR_LEN);
+		struct in6_addr *pin6;
+		__be32 *p32;
+
+		__entry->family = n->tbl->family;
+		__assign_str(dev);
+		__entry->lladdr_len = lladdr_len;
+		memcpy(__entry->lladdr, n->ha, lladdr_len);
+		__entry->flags = n->flags;
+		__entry->nud_state = n->nud_state;
+		__entry->type = n->type;
+		__entry->dead = n->dead;
+		__entry->refcnt = refcount_read(&n->refcnt);
+		pin6 = (struct in6_addr *)__entry->primary_key6;
+		p32 = (__be32 *)__entry->primary_key4;
+
+		if (n->tbl->family == AF_INET)
+			*p32 = *(__be32 *)n->primary_key;
+		else
+			*p32 = 0;
+
+#if IS_ENABLED(CONFIG_IPV6)
+		if (n->tbl->family == AF_INET6) {
+			pin6 = (struct in6_addr *)__entry->primary_key6;
+			*pin6 = *(struct in6_addr *)n->primary_key;
+		} else
+#endif
+		{
+			ipv6_addr_set_v4mapped(*p32, pin6);
+		}
+
+		__entry->confirmed = n->confirmed;
+		__entry->updated = n->updated;
+		__entry->used = n->used;
+		__entry->err = err;
+	),
+
+	TP_printk("family %d dev %s lladdr %s flags %02x nud_state %s type %02x "
+		  "dead %d refcnt %d primary_key4 %pI4 primary_key6 %pI6c "
+		  "confirmed %lu updated %lu used %lu err %d",
+		  __entry->family, __get_str(dev),
+		  __print_hex_str(__entry->lladdr, __entry->lladdr_len),
+		  __entry->flags, neigh_state_str(__entry->nud_state),
+		  __entry->type, __entry->dead, __entry->refcnt,
+		  __entry->primary_key4, __entry->primary_key6,
+		  __entry->confirmed, __entry->updated, __entry->used,
+		  __entry->err)
+);
+
+DEFINE_EVENT(neigh__update, neigh_update_done,
+	TP_PROTO(struct neighbour *neigh, int err),
+	TP_ARGS(neigh, err)
+);
+
+DEFINE_EVENT(neigh__update, neigh_timer_handler,
+	TP_PROTO(struct neighbour *neigh, int err),
+	TP_ARGS(neigh, err)
+);
+
+DEFINE_EVENT(neigh__update, neigh_event_send_done,
+	TP_PROTO(struct neighbour *neigh, int err),
+	TP_ARGS(neigh, err)
+);
+
+DEFINE_EVENT(neigh__update, neigh_event_send_dead,
+	TP_PROTO(struct neighbour *neigh, int err),
+	TP_ARGS(neigh, err)
+);
+
+DEFINE_EVENT(neigh__update, neigh_cleanup_and_release,
+	TP_PROTO(struct neighbour *neigh, int rc),
+	TP_ARGS(neigh, rc)
+);
+
+#endif /* _TRACE_NEIGH_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>