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, 223 insertions, 0 deletions

diff --git a/include/trace/events/oom.h b/include/trace/events/oom.h
new file mode 100644
index 000000000..9f0a5d148
--- /dev/null
+++ b/include/trace/events/oom.h
@@ -0,0 +1,223 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM oom
+
+#if !defined(_TRACE_OOM_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_OOM_H
+#include <linux/tracepoint.h>
+#include <trace/events/mmflags.h>
+
+#define PG_COUNT_TO_KB(x) ((x) << (PAGE_SHIFT - 10))
+
+TRACE_EVENT(oom_score_adj_update,
+
+	TP_PROTO(struct task_struct *task),
+
+	TP_ARGS(task),
+
+	TP_STRUCT__entry(
+		__field(	pid_t,	pid)
+		__array(	char,	comm,	TASK_COMM_LEN )
+		__field(	short,	oom_score_adj)
+	),
+
+	TP_fast_assign(
+		__entry->pid = task->pid;
+		memcpy(__entry->comm, task->comm, TASK_COMM_LEN);
+		__entry->oom_score_adj = task->signal->oom_score_adj;
+	),
+
+	TP_printk("pid=%d comm=%s oom_score_adj=%hd",
+		__entry->pid, __entry->comm, __entry->oom_score_adj)
+);
+
+TRACE_EVENT(reclaim_retry_zone,
+
+	TP_PROTO(struct zoneref *zoneref,
+		int order,
+		unsigned long reclaimable,
+		unsigned long available,
+		unsigned long min_wmark,
+		int no_progress_loops,
+		bool wmark_check),
+
+	TP_ARGS(zoneref, order, reclaimable, available, min_wmark, no_progress_loops, wmark_check),
+
+	TP_STRUCT__entry(
+		__field(	int, node)
+		__field(	int, zone_idx)
+		__field(	int,	order)
+		__field(	unsigned long,	reclaimable)
+		__field(	unsigned long,	available)
+		__field(	unsigned long,	min_wmark)
+		__field(	int,	no_progress_loops)
+		__field(	bool,	wmark_check)
+	),
+
+	TP_fast_assign(
+		__entry->node = zonelist_node_idx(zoneref);
+		__entry->zone_idx = zonelist_zone_idx(zoneref);
+		__entry->order = order;
+		__entry->reclaimable = reclaimable;
+		__entry->available = available;
+		__entry->min_wmark = min_wmark;
+		__entry->no_progress_loops = no_progress_loops;
+		__entry->wmark_check = wmark_check;
+	),
+
+	TP_printk("node=%d zone=%-8s order=%d reclaimable=%lu available=%lu min_wmark=%lu no_progress_loops=%d wmark_check=%d",
+			__entry->node, __print_symbolic(__entry->zone_idx, ZONE_TYPE),
+			__entry->order,
+			__entry->reclaimable, __entry->available, __entry->min_wmark,
+			__entry->no_progress_loops,
+			__entry->wmark_check)
+);
+
+TRACE_EVENT(mark_victim,
+	TP_PROTO(struct task_struct *task, uid_t uid),
+
+	TP_ARGS(task, uid),
+
+	TP_STRUCT__entry(
+		__field(int, pid)
+		__string(comm, task->comm)
+		__field(unsigned long, total_vm)
+		__field(unsigned long, anon_rss)
+		__field(unsigned long, file_rss)
+		__field(unsigned long, shmem_rss)
+		__field(uid_t, uid)
+		__field(unsigned long, pgtables)
+		__field(short, oom_score_adj)
+	),
+
+	TP_fast_assign(
+		__entry->pid = task->pid;
+		__assign_str(comm);
+		__entry->total_vm = PG_COUNT_TO_KB(task->mm->total_vm);
+		__entry->anon_rss = PG_COUNT_TO_KB(get_mm_counter(task->mm, MM_ANONPAGES));
+		__entry->file_rss = PG_COUNT_TO_KB(get_mm_counter(task->mm, MM_FILEPAGES));
+		__entry->shmem_rss = PG_COUNT_TO_KB(get_mm_counter(task->mm, MM_SHMEMPAGES));
+		__entry->uid = uid;
+		__entry->pgtables = mm_pgtables_bytes(task->mm) >> 10;
+		__entry->oom_score_adj = task->signal->oom_score_adj;
+	),
+
+	TP_printk("pid=%d comm=%s total-vm=%lukB anon-rss=%lukB file-rss:%lukB shmem-rss:%lukB uid=%u pgtables=%lukB oom_score_adj=%hd",
+		__entry->pid,
+		__get_str(comm),
+		__entry->total_vm,
+		__entry->anon_rss,
+		__entry->file_rss,
+		__entry->shmem_rss,
+		__entry->uid,
+		__entry->pgtables,
+		__entry->oom_score_adj
+	)
+);
+
+TRACE_EVENT(wake_reaper,
+	TP_PROTO(int pid),
+
+	TP_ARGS(pid),
+
+	TP_STRUCT__entry(
+		__field(int, pid)
+	),
+
+	TP_fast_assign(
+		__entry->pid = pid;
+	),
+
+	TP_printk("pid=%d", __entry->pid)
+);
+
+TRACE_EVENT(start_task_reaping,
+	TP_PROTO(int pid),
+
+	TP_ARGS(pid),
+
+	TP_STRUCT__entry(
+		__field(int, pid)
+	),
+
+	TP_fast_assign(
+		__entry->pid = pid;
+	),
+
+	TP_printk("pid=%d", __entry->pid)
+);
+
+TRACE_EVENT(finish_task_reaping,
+	TP_PROTO(int pid),
+
+	TP_ARGS(pid),
+
+	TP_STRUCT__entry(
+		__field(int, pid)
+	),
+
+	TP_fast_assign(
+		__entry->pid = pid;
+	),
+
+	TP_printk("pid=%d", __entry->pid)
+);
+
+TRACE_EVENT(skip_task_reaping,
+	TP_PROTO(int pid),
+
+	TP_ARGS(pid),
+
+	TP_STRUCT__entry(
+		__field(int, pid)
+	),
+
+	TP_fast_assign(
+		__entry->pid = pid;
+	),
+
+	TP_printk("pid=%d", __entry->pid)
+);
+
+#ifdef CONFIG_COMPACTION
+TRACE_EVENT(compact_retry,
+
+	TP_PROTO(int order,
+		enum compact_priority priority,
+		enum compact_result result,
+		int retries,
+		int max_retries,
+		bool ret),
+
+	TP_ARGS(order, priority, result, retries, max_retries, ret),
+
+	TP_STRUCT__entry(
+		__field(	int, order)
+		__field(	int, priority)
+		__field(	int, result)
+		__field(	int, retries)
+		__field(	int, max_retries)
+		__field(	bool, ret)
+	),
+
+	TP_fast_assign(
+		__entry->order = order;
+		__entry->priority = priority;
+		__entry->result = compact_result_to_feedback(result);
+		__entry->retries = retries;
+		__entry->max_retries = max_retries;
+		__entry->ret = ret;
+	),
+
+	TP_printk("order=%d priority=%s compaction_result=%s retries=%d max_retries=%d should_retry=%d",
+			__entry->order,
+			__print_symbolic(__entry->priority, COMPACTION_PRIORITY),
+			__print_symbolic(__entry->result, COMPACTION_FEEDBACK),
+			__entry->retries, __entry->max_retries,
+			__entry->ret)
+);
+#endif /* CONFIG_COMPACTION */
+#endif
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>