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, 242 insertions, 0 deletions

diff --git a/drivers/misc/ocxl/trace.h b/drivers/misc/ocxl/trace.h
new file mode 100644
index 000000000..a33a5094f
--- /dev/null
+++ b/drivers/misc/ocxl/trace.h
@@ -0,0 +1,242 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+// Copyright 2017 IBM Corp.
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM ocxl
+
+#if !defined(_TRACE_OCXL_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_OCXL_H
+
+#include <linux/tracepoint.h>
+
+
+TRACE_EVENT(ocxl_mmu_notifier_range,
+	TP_PROTO(unsigned long start, unsigned long end, unsigned long pidr),
+	TP_ARGS(start, end, pidr),
+
+	TP_STRUCT__entry(
+		__field(unsigned long, start)
+		__field(unsigned long, end)
+		__field(unsigned long, pidr)
+	),
+
+	TP_fast_assign(
+		__entry->start = start;
+		__entry->end = end;
+		__entry->pidr = pidr;
+	),
+
+	TP_printk("start=0x%lx end=0x%lx pidr=0x%lx",
+		__entry->start,
+		__entry->end,
+		__entry->pidr
+	)
+);
+
+TRACE_EVENT(ocxl_init_mmu_notifier,
+	TP_PROTO(int pasid, unsigned long pidr),
+	TP_ARGS(pasid, pidr),
+
+	TP_STRUCT__entry(
+		__field(int, pasid)
+		__field(unsigned long, pidr)
+	),
+
+	TP_fast_assign(
+		__entry->pasid = pasid;
+		__entry->pidr = pidr;
+	),
+
+	TP_printk("pasid=%d, pidr=0x%lx",
+		__entry->pasid,
+		__entry->pidr
+	)
+);
+
+TRACE_EVENT(ocxl_release_mmu_notifier,
+	TP_PROTO(int pasid, unsigned long pidr),
+	TP_ARGS(pasid, pidr),
+
+	TP_STRUCT__entry(
+		__field(int, pasid)
+		__field(unsigned long, pidr)
+	),
+
+	TP_fast_assign(
+		__entry->pasid = pasid;
+		__entry->pidr = pidr;
+	),
+
+	TP_printk("pasid=%d, pidr=0x%lx",
+		__entry->pasid,
+		__entry->pidr
+	)
+);
+
+DECLARE_EVENT_CLASS(ocxl_context,
+	TP_PROTO(pid_t pid, void *spa, int pasid, u32 pidr, u32 tidr),
+	TP_ARGS(pid, spa, pasid, pidr, tidr),
+
+	TP_STRUCT__entry(
+		__field(pid_t, pid)
+		__field(void*, spa)
+		__field(int, pasid)
+		__field(u32, pidr)
+		__field(u32, tidr)
+	),
+
+	TP_fast_assign(
+		__entry->pid = pid;
+		__entry->spa = spa;
+		__entry->pasid = pasid;
+		__entry->pidr = pidr;
+		__entry->tidr = tidr;
+	),
+
+	TP_printk("linux pid=%d spa=0x%p pasid=0x%x pidr=0x%x tidr=0x%x",
+		__entry->pid,
+		__entry->spa,
+		__entry->pasid,
+		__entry->pidr,
+		__entry->tidr
+	)
+);
+
+DEFINE_EVENT(ocxl_context, ocxl_context_add,
+	TP_PROTO(pid_t pid, void *spa, int pasid, u32 pidr, u32 tidr),
+	TP_ARGS(pid, spa, pasid, pidr, tidr)
+);
+
+DEFINE_EVENT(ocxl_context, ocxl_context_remove,
+	TP_PROTO(pid_t pid, void *spa, int pasid, u32 pidr, u32 tidr),
+	TP_ARGS(pid, spa, pasid, pidr, tidr)
+);
+
+TRACE_EVENT(ocxl_terminate_pasid,
+	TP_PROTO(int pasid, int rc),
+	TP_ARGS(pasid, rc),
+
+	TP_STRUCT__entry(
+		__field(int, pasid)
+		__field(int, rc)
+	),
+
+	TP_fast_assign(
+		__entry->pasid = pasid;
+		__entry->rc = rc;
+	),
+
+	TP_printk("pasid=0x%x rc=%d",
+		__entry->pasid,
+		__entry->rc
+	)
+);
+
+DECLARE_EVENT_CLASS(ocxl_fault_handler,
+	TP_PROTO(void *spa, u64 pe, u64 dsisr, u64 dar, u64 tfc),
+	TP_ARGS(spa, pe, dsisr, dar, tfc),
+
+	TP_STRUCT__entry(
+		__field(void *, spa)
+		__field(u64, pe)
+		__field(u64, dsisr)
+		__field(u64, dar)
+		__field(u64, tfc)
+	),
+
+	TP_fast_assign(
+		__entry->spa = spa;
+		__entry->pe = pe;
+		__entry->dsisr = dsisr;
+		__entry->dar = dar;
+		__entry->tfc = tfc;
+	),
+
+	TP_printk("spa=%p pe=0x%llx dsisr=0x%llx dar=0x%llx tfc=0x%llx",
+		__entry->spa,
+		__entry->pe,
+		__entry->dsisr,
+		__entry->dar,
+		__entry->tfc
+	)
+);
+
+DEFINE_EVENT(ocxl_fault_handler, ocxl_fault,
+	TP_PROTO(void *spa, u64 pe, u64 dsisr, u64 dar, u64 tfc),
+	TP_ARGS(spa, pe, dsisr, dar, tfc)
+);
+
+DEFINE_EVENT(ocxl_fault_handler, ocxl_fault_ack,
+	TP_PROTO(void *spa, u64 pe, u64 dsisr, u64 dar, u64 tfc),
+	TP_ARGS(spa, pe, dsisr, dar, tfc)
+);
+
+TRACE_EVENT(ocxl_afu_irq_alloc,
+	TP_PROTO(int pasid, int irq_id, unsigned int virq, int hw_irq),
+	TP_ARGS(pasid, irq_id, virq, hw_irq),
+
+	TP_STRUCT__entry(
+		__field(int, pasid)
+		__field(int, irq_id)
+		__field(unsigned int, virq)
+		__field(int, hw_irq)
+	),
+
+	TP_fast_assign(
+		__entry->pasid = pasid;
+		__entry->irq_id = irq_id;
+		__entry->virq = virq;
+		__entry->hw_irq = hw_irq;
+	),
+
+	TP_printk("pasid=0x%x irq_id=%d virq=%u hw_irq=%d",
+		__entry->pasid,
+		__entry->irq_id,
+		__entry->virq,
+		__entry->hw_irq
+	)
+);
+
+TRACE_EVENT(ocxl_afu_irq_free,
+	TP_PROTO(int pasid, int irq_id),
+	TP_ARGS(pasid, irq_id),
+
+	TP_STRUCT__entry(
+		__field(int, pasid)
+		__field(int, irq_id)
+	),
+
+	TP_fast_assign(
+		__entry->pasid = pasid;
+		__entry->irq_id = irq_id;
+	),
+
+	TP_printk("pasid=0x%x irq_id=%d",
+		__entry->pasid,
+		__entry->irq_id
+	)
+);
+
+TRACE_EVENT(ocxl_afu_irq_receive,
+	TP_PROTO(int virq),
+	TP_ARGS(virq),
+
+	TP_STRUCT__entry(
+		__field(int, virq)
+	),
+
+	TP_fast_assign(
+		__entry->virq = virq;
+	),
+
+	TP_printk("virq=%d",
+		__entry->virq
+	)
+);
+
+#endif /* _TRACE_OCXL_H */
+
+/* This part must be outside protection */
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH .
+#define TRACE_INCLUDE_FILE trace
+#include <trace/define_trace.h>