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, 84 insertions, 0 deletions

diff --git a/drivers/md/dm-audit.c b/drivers/md/dm-audit.c
new file mode 100644
index 000000000..2e979eeb1
--- /dev/null
+++ b/drivers/md/dm-audit.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Creating audit records for mapped devices.
+ *
+ * Copyright (C) 2021 Fraunhofer AISEC. All rights reserved.
+ *
+ * Authors: Michael Weiß <michael.weiss@aisec.fraunhofer.de>
+ */
+
+#include <linux/audit.h>
+#include <linux/module.h>
+#include <linux/device-mapper.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+
+#include "dm-audit.h"
+#include "dm-core.h"
+
+static struct audit_buffer *dm_audit_log_start(int audit_type,
+					       const char *dm_msg_prefix,
+					       const char *op)
+{
+	struct audit_buffer *ab;
+
+	if (audit_enabled == AUDIT_OFF)
+		return NULL;
+
+	ab = audit_log_start(audit_context(), GFP_KERNEL, audit_type);
+	if (unlikely(!ab))
+		return NULL;
+
+	audit_log_format(ab, "module=%s op=%s", dm_msg_prefix, op);
+	return ab;
+}
+
+void dm_audit_log_ti(int audit_type, const char *dm_msg_prefix, const char *op,
+		     struct dm_target *ti, int result)
+{
+	struct audit_buffer *ab = NULL;
+	struct mapped_device *md = dm_table_get_md(ti->table);
+	int dev_major = dm_disk(md)->major;
+	int dev_minor = dm_disk(md)->first_minor;
+
+	switch (audit_type) {
+	case AUDIT_DM_CTRL:
+		ab = dm_audit_log_start(audit_type, dm_msg_prefix, op);
+		if (unlikely(!ab))
+			return;
+		audit_log_task_info(ab);
+		audit_log_format(ab, " dev=%d:%d error_msg='%s'", dev_major,
+				 dev_minor, !result ? ti->error : "success");
+		break;
+	case AUDIT_DM_EVENT:
+		ab = dm_audit_log_start(audit_type, dm_msg_prefix, op);
+		if (unlikely(!ab))
+			return;
+		audit_log_format(ab, " dev=%d:%d sector=?", dev_major,
+				 dev_minor);
+		break;
+	default: /* unintended use */
+		return;
+	}
+
+	audit_log_format(ab, " res=%d", result);
+	audit_log_end(ab);
+}
+EXPORT_SYMBOL_GPL(dm_audit_log_ti);
+
+void dm_audit_log_bio(const char *dm_msg_prefix, const char *op,
+		      struct bio *bio, sector_t sector, int result)
+{
+	struct audit_buffer *ab;
+	int dev_major = MAJOR(bio->bi_bdev->bd_dev);
+	int dev_minor = MINOR(bio->bi_bdev->bd_dev);
+
+	ab = dm_audit_log_start(AUDIT_DM_EVENT, dm_msg_prefix, op);
+	if (unlikely(!ab))
+		return;
+
+	audit_log_format(ab, " dev=%d:%d sector=%llu res=%d",
+			 dev_major, dev_minor, sector, result);
+	audit_log_end(ab);
+}
+EXPORT_SYMBOL_GPL(dm_audit_log_bio);