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, 94 insertions, 0 deletions

diff --git a/drivers/dca/dca-sysfs.c b/drivers/dca/dca-sysfs.c
new file mode 100644
index 000000000..b915c2b46
--- /dev/null
+++ b/drivers/dca/dca-sysfs.c
@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright(c) 2007 - 2009 Intel Corporation. All rights reserved.
+ */
+
+#include <linux/kernel.h>
+#include <linux/spinlock.h>
+#include <linux/device.h>
+#include <linux/idr.h>
+#include <linux/kdev_t.h>
+#include <linux/err.h>
+#include <linux/dca.h>
+#include <linux/gfp.h>
+#include <linux/export.h>
+
+static const struct class dca_class = {
+	.name = "dca",
+};
+static struct idr dca_idr;
+static spinlock_t dca_idr_lock;
+
+int dca_sysfs_add_req(struct dca_provider *dca, struct device *dev, int slot)
+{
+	struct device *cd;
+	static int req_count;
+
+	cd = device_create(&dca_class, dca->cd, MKDEV(0, slot + 1), NULL,
+			   "requester%d", req_count++);
+	return PTR_ERR_OR_ZERO(cd);
+}
+
+void dca_sysfs_remove_req(struct dca_provider *dca, int slot)
+{
+	device_destroy(&dca_class, MKDEV(0, slot + 1));
+}
+
+int dca_sysfs_add_provider(struct dca_provider *dca, struct device *dev)
+{
+	struct device *cd;
+	int ret;
+
+	idr_preload(GFP_KERNEL);
+	spin_lock(&dca_idr_lock);
+
+	ret = idr_alloc(&dca_idr, dca, 0, 0, GFP_NOWAIT);
+	if (ret >= 0)
+		dca->id = ret;
+
+	spin_unlock(&dca_idr_lock);
+	idr_preload_end();
+	if (ret < 0)
+		return ret;
+
+	cd = device_create(&dca_class, dev, MKDEV(0, 0), NULL, "dca%d", dca->id);
+	if (IS_ERR(cd)) {
+		spin_lock(&dca_idr_lock);
+		idr_remove(&dca_idr, dca->id);
+		spin_unlock(&dca_idr_lock);
+		return PTR_ERR(cd);
+	}
+	dca->cd = cd;
+	return 0;
+}
+
+void dca_sysfs_remove_provider(struct dca_provider *dca)
+{
+	device_unregister(dca->cd);
+	dca->cd = NULL;
+	spin_lock(&dca_idr_lock);
+	idr_remove(&dca_idr, dca->id);
+	spin_unlock(&dca_idr_lock);
+}
+
+int __init dca_sysfs_init(void)
+{
+	int err;
+
+	idr_init(&dca_idr);
+	spin_lock_init(&dca_idr_lock);
+
+	err = class_register(&dca_class);
+	if (err) {
+		idr_destroy(&dca_idr);
+		return err;
+	}
+	return 0;
+}
+
+void __exit dca_sysfs_exit(void)
+{
+	class_unregister(&dca_class);
+	idr_destroy(&dca_idr);
+}
+