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, 384 insertions, 0 deletions

diff --git a/include/trace/events/xdp.h b/include/trace/events/xdp.h
new file mode 100644
index 000000000..18c0ac514
--- /dev/null
+++ b/include/trace/events/xdp.h
@@ -0,0 +1,384 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM xdp
+
+#if !defined(_TRACE_XDP_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_XDP_H
+
+#include <linux/netdevice.h>
+#include <linux/filter.h>
+#include <linux/tracepoint.h>
+#include <linux/bpf.h>
+#include <net/xdp.h>
+
+#define __XDP_ACT_MAP(FN)	\
+	FN(ABORTED)		\
+	FN(DROP)		\
+	FN(PASS)		\
+	FN(TX)			\
+	FN(REDIRECT)
+
+#define __XDP_ACT_TP_FN(x)	\
+	TRACE_DEFINE_ENUM(XDP_##x);
+#define __XDP_ACT_SYM_FN(x)	\
+	{ XDP_##x, #x },
+#define __XDP_ACT_SYM_TAB	\
+	__XDP_ACT_MAP(__XDP_ACT_SYM_FN) { -1, NULL }
+__XDP_ACT_MAP(__XDP_ACT_TP_FN)
+
+TRACE_EVENT(xdp_exception,
+
+	TP_PROTO(const struct net_device *dev,
+		 const struct bpf_prog *xdp, u32 act),
+
+	TP_ARGS(dev, xdp, act),
+
+	TP_STRUCT__entry(
+		__field(int, prog_id)
+		__field(u32, act)
+		__field(int, ifindex)
+	),
+
+	TP_fast_assign(
+		__entry->prog_id	= xdp->aux->id;
+		__entry->act		= act;
+		__entry->ifindex	= dev->ifindex;
+	),
+
+	TP_printk("prog_id=%d action=%s ifindex=%d",
+		  __entry->prog_id,
+		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
+		  __entry->ifindex)
+);
+
+TRACE_EVENT(xdp_bulk_tx,
+
+	TP_PROTO(const struct net_device *dev,
+		 int sent, int drops, int err),
+
+	TP_ARGS(dev, sent, drops, err),
+
+	TP_STRUCT__entry(
+		__field(int, ifindex)
+		__field(u32, act)
+		__field(int, drops)
+		__field(int, sent)
+		__field(int, err)
+	),
+
+	TP_fast_assign(
+		__entry->ifindex	= dev->ifindex;
+		__entry->act		= XDP_TX;
+		__entry->drops		= drops;
+		__entry->sent		= sent;
+		__entry->err		= err;
+	),
+
+	TP_printk("ifindex=%d action=%s sent=%d drops=%d err=%d",
+		  __entry->ifindex,
+		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
+		  __entry->sent, __entry->drops, __entry->err)
+);
+
+#ifndef __DEVMAP_OBJ_TYPE
+#define __DEVMAP_OBJ_TYPE
+struct _bpf_dtab_netdev {
+	struct net_device *dev;
+};
+#endif /* __DEVMAP_OBJ_TYPE */
+
+DECLARE_EVENT_CLASS(xdp_redirect_template,
+
+	TP_PROTO(const struct net_device *dev,
+		 const struct bpf_prog *xdp,
+		 const void *tgt, int err,
+		 enum bpf_map_type map_type,
+		 u32 map_id, u32 index),
+
+	TP_ARGS(dev, xdp, tgt, err, map_type, map_id, index),
+
+	TP_STRUCT__entry(
+		__field(int, prog_id)
+		__field(u32, act)
+		__field(int, ifindex)
+		__field(int, err)
+		__field(int, to_ifindex)
+		__field(u32, map_id)
+		__field(int, map_index)
+	),
+
+	TP_fast_assign(
+		u32 ifindex = 0, map_index = index;
+
+		if (map_type == BPF_MAP_TYPE_DEVMAP || map_type == BPF_MAP_TYPE_DEVMAP_HASH) {
+			/* Just leave to_ifindex to 0 if do broadcast redirect,
+			 * as tgt will be NULL.
+			 */
+			if (tgt)
+				ifindex = ((struct _bpf_dtab_netdev *)tgt)->dev->ifindex;
+		} else if (map_type == BPF_MAP_TYPE_UNSPEC && map_id == INT_MAX) {
+			ifindex = index;
+			map_index = 0;
+		}
+
+		__entry->prog_id	= xdp->aux->id;
+		__entry->act		= XDP_REDIRECT;
+		__entry->ifindex	= dev->ifindex;
+		__entry->err		= err;
+		__entry->to_ifindex	= ifindex;
+		__entry->map_id		= map_id;
+		__entry->map_index	= map_index;
+	),
+
+	TP_printk("prog_id=%d action=%s ifindex=%d to_ifindex=%d err=%d"
+		  " map_id=%d map_index=%d",
+		  __entry->prog_id,
+		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
+		  __entry->ifindex, __entry->to_ifindex,
+		  __entry->err, __entry->map_id, __entry->map_index)
+);
+
+DEFINE_EVENT(xdp_redirect_template, xdp_redirect,
+	TP_PROTO(const struct net_device *dev,
+		 const struct bpf_prog *xdp,
+		 const void *tgt, int err,
+		 enum bpf_map_type map_type,
+		 u32 map_id, u32 index),
+	TP_ARGS(dev, xdp, tgt, err, map_type, map_id, index)
+);
+
+DEFINE_EVENT(xdp_redirect_template, xdp_redirect_err,
+	TP_PROTO(const struct net_device *dev,
+		 const struct bpf_prog *xdp,
+		 const void *tgt, int err,
+		 enum bpf_map_type map_type,
+		 u32 map_id, u32 index),
+	TP_ARGS(dev, xdp, tgt, err, map_type, map_id, index)
+);
+
+#define _trace_xdp_redirect(dev, xdp, to)						\
+	 trace_xdp_redirect(dev, xdp, NULL, 0, BPF_MAP_TYPE_UNSPEC, INT_MAX, to)
+
+#define _trace_xdp_redirect_err(dev, xdp, to, err)					\
+	 trace_xdp_redirect_err(dev, xdp, NULL, err, BPF_MAP_TYPE_UNSPEC, INT_MAX, to)
+
+#define _trace_xdp_redirect_map(dev, xdp, to, map_type, map_id, index) \
+	 trace_xdp_redirect(dev, xdp, to, 0, map_type, map_id, index)
+
+#define _trace_xdp_redirect_map_err(dev, xdp, to, map_type, map_id, index, err) \
+	 trace_xdp_redirect_err(dev, xdp, to, err, map_type, map_id, index)
+
+#ifdef CONFIG_BPF_SYSCALL
+TRACE_EVENT(xdp_cpumap_kthread,
+
+	TP_PROTO(int map_id, unsigned int processed,  unsigned int drops,
+		 int sched, struct xdp_cpumap_stats *xdp_stats),
+
+	TP_ARGS(map_id, processed, drops, sched, xdp_stats),
+
+	TP_STRUCT__entry(
+		__field(int, map_id)
+		__field(u32, act)
+		__field(int, cpu)
+		__field(unsigned int, drops)
+		__field(unsigned int, processed)
+		__field(int, sched)
+		__field(unsigned int, xdp_pass)
+		__field(unsigned int, xdp_drop)
+		__field(unsigned int, xdp_redirect)
+	),
+
+	TP_fast_assign(
+		__entry->map_id		= map_id;
+		__entry->act		= XDP_REDIRECT;
+		__entry->cpu		= smp_processor_id();
+		__entry->drops		= drops;
+		__entry->processed	= processed;
+		__entry->sched	= sched;
+		__entry->xdp_pass	= xdp_stats->pass;
+		__entry->xdp_drop	= xdp_stats->drop;
+		__entry->xdp_redirect	= xdp_stats->redirect;
+	),
+
+	TP_printk("kthread"
+		  " cpu=%d map_id=%d action=%s"
+		  " processed=%u drops=%u"
+		  " sched=%d"
+		  " xdp_pass=%u xdp_drop=%u xdp_redirect=%u",
+		  __entry->cpu, __entry->map_id,
+		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
+		  __entry->processed, __entry->drops,
+		  __entry->sched,
+		  __entry->xdp_pass, __entry->xdp_drop, __entry->xdp_redirect)
+);
+
+TRACE_EVENT(xdp_cpumap_enqueue,
+
+	TP_PROTO(int map_id, unsigned int processed,  unsigned int drops,
+		 int to_cpu),
+
+	TP_ARGS(map_id, processed, drops, to_cpu),
+
+	TP_STRUCT__entry(
+		__field(int, map_id)
+		__field(u32, act)
+		__field(int, cpu)
+		__field(unsigned int, drops)
+		__field(unsigned int, processed)
+		__field(int, to_cpu)
+	),
+
+	TP_fast_assign(
+		__entry->map_id		= map_id;
+		__entry->act		= XDP_REDIRECT;
+		__entry->cpu		= smp_processor_id();
+		__entry->drops		= drops;
+		__entry->processed	= processed;
+		__entry->to_cpu		= to_cpu;
+	),
+
+	TP_printk("enqueue"
+		  " cpu=%d map_id=%d action=%s"
+		  " processed=%u drops=%u"
+		  " to_cpu=%d",
+		  __entry->cpu, __entry->map_id,
+		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
+		  __entry->processed, __entry->drops,
+		  __entry->to_cpu)
+);
+
+TRACE_EVENT(xdp_devmap_xmit,
+
+	TP_PROTO(const struct net_device *from_dev,
+		 const struct net_device *to_dev,
+		 int sent, int drops, int err),
+
+	TP_ARGS(from_dev, to_dev, sent, drops, err),
+
+	TP_STRUCT__entry(
+		__field(int, from_ifindex)
+		__field(u32, act)
+		__field(int, to_ifindex)
+		__field(int, drops)
+		__field(int, sent)
+		__field(int, err)
+	),
+
+	TP_fast_assign(
+		__entry->from_ifindex	= from_dev->ifindex;
+		__entry->act		= XDP_REDIRECT;
+		__entry->to_ifindex	= to_dev->ifindex;
+		__entry->drops		= drops;
+		__entry->sent		= sent;
+		__entry->err		= err;
+	),
+
+	TP_printk("ndo_xdp_xmit"
+		  " from_ifindex=%d to_ifindex=%d action=%s"
+		  " sent=%d drops=%d"
+		  " err=%d",
+		  __entry->from_ifindex, __entry->to_ifindex,
+		  __print_symbolic(__entry->act, __XDP_ACT_SYM_TAB),
+		  __entry->sent, __entry->drops,
+		  __entry->err)
+);
+#endif /* CONFIG_BPF_SYSCALL */
+
+/* Expect users already include <net/xdp.h>, but not xdp_priv.h */
+#include <net/xdp_priv.h>
+
+#define __MEM_TYPE_MAP(FN)	\
+	FN(PAGE_SHARED)		\
+	FN(PAGE_ORDER0)		\
+	FN(PAGE_POOL)		\
+	FN(XSK_BUFF_POOL)
+
+#define __MEM_TYPE_TP_FN(x)	\
+	TRACE_DEFINE_ENUM(MEM_TYPE_##x);
+#define __MEM_TYPE_SYM_FN(x)	\
+	{ MEM_TYPE_##x, #x },
+#define __MEM_TYPE_SYM_TAB	\
+	__MEM_TYPE_MAP(__MEM_TYPE_SYM_FN) { -1, 0 }
+__MEM_TYPE_MAP(__MEM_TYPE_TP_FN)
+
+TRACE_EVENT(mem_disconnect,
+
+	TP_PROTO(const struct xdp_mem_allocator *xa),
+
+	TP_ARGS(xa),
+
+	TP_STRUCT__entry(
+		__field(const struct xdp_mem_allocator *,	xa)
+		__field(u32,		mem_id)
+		__field(u32,		mem_type)
+		__field(const void *,	allocator)
+	),
+
+	TP_fast_assign(
+		__entry->xa		= xa;
+		__entry->mem_id		= xa->mem.id;
+		__entry->mem_type	= xa->mem.type;
+		__entry->allocator	= xa->allocator;
+	),
+
+	TP_printk("mem_id=%d mem_type=%s allocator=%p",
+		  __entry->mem_id,
+		  __print_symbolic(__entry->mem_type, __MEM_TYPE_SYM_TAB),
+		  __entry->allocator
+	)
+);
+
+TRACE_EVENT(mem_connect,
+
+	TP_PROTO(const struct xdp_mem_allocator *xa,
+		 const struct xdp_rxq_info *rxq),
+
+	TP_ARGS(xa, rxq),
+
+	TP_STRUCT__entry(
+		__field(const struct xdp_mem_allocator *,	xa)
+		__field(u32,		mem_id)
+		__field(u32,		mem_type)
+		__field(const void *,	allocator)
+		__field(const struct xdp_rxq_info *,		rxq)
+		__field(int,		ifindex)
+	),
+
+	TP_fast_assign(
+		__entry->xa		= xa;
+		__entry->mem_id		= xa->mem.id;
+		__entry->mem_type	= xa->mem.type;
+		__entry->allocator	= xa->allocator;
+		__entry->rxq		= rxq;
+		__entry->ifindex	= rxq->dev->ifindex;
+	),
+
+	TP_printk("mem_id=%d mem_type=%s allocator=%p"
+		  " ifindex=%d",
+		  __entry->mem_id,
+		  __print_symbolic(__entry->mem_type, __MEM_TYPE_SYM_TAB),
+		  __entry->allocator,
+		  __entry->ifindex
+	)
+);
+
+TRACE_EVENT(bpf_xdp_link_attach_failed,
+
+	TP_PROTO(const char *msg),
+
+	TP_ARGS(msg),
+
+	TP_STRUCT__entry(
+		__string(msg, msg)
+	),
+
+	TP_fast_assign(
+		__assign_str(msg);
+	),
+
+	TP_printk("errmsg=%s", __get_str(msg))
+);
+
+#endif /* _TRACE_XDP_H */
+
+#include <trace/define_trace.h>