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, 77 insertions, 0 deletions

diff --git a/drivers/scsi/sr.h b/drivers/scsi/sr.h
new file mode 100644
index 000000000..2d92f9cb6
--- /dev/null
+++ b/drivers/scsi/sr.h
@@ -0,0 +1,77 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ *      sr.h by David Giller
+ *      CD-ROM disk driver header file
+ *      
+ *      adapted from:
+ *      sd.h Copyright (C) 1992 Drew Eckhardt 
+ *      SCSI disk driver header file by
+ *              Drew Eckhardt 
+ *
+ *      <drew@colorado.edu>
+ *
+ *       Modified by Eric Youngdale eric@andante.org to
+ *       add scatter-gather, multiple outstanding request, and other
+ *       enhancements.
+ */
+
+#ifndef _SR_H
+#define _SR_H
+
+#include <linux/mutex.h>
+
+#define MAX_RETRIES	3
+#define SR_TIMEOUT	(30 * HZ)
+
+struct scsi_device;
+
+/* The CDROM is fairly slow, so we need a little extra time */
+/* In fact, it is very slow if it has to spin up first */
+#define IOCTL_TIMEOUT 30*HZ
+
+
+typedef struct scsi_cd {
+	unsigned capacity;	/* size in blocks                       */
+	struct scsi_device *device;
+	unsigned int vendor;	/* vendor code, see sr_vendor.c         */
+	unsigned long ms_offset;	/* for reading multisession-CD's        */
+	unsigned use:1;		/* is this device still supportable     */
+	unsigned xa_flag:1;	/* CD has XA sectors ? */
+	unsigned readcd_known:1;	/* drive supports READ_CD (0xbe) */
+	unsigned readcd_cdda:1;	/* reading audio data using READ_CD */
+	unsigned media_present:1;	/* media is present */
+
+	/* GET_EVENT spurious event handling, blk layer guarantees exclusion */
+	int tur_mismatch;		/* nr of get_event TUR mismatches */
+	bool tur_changed:1;		/* changed according to TUR */
+	bool get_event_changed:1;	/* changed according to GET_EVENT */
+	bool ignore_get_event:1;	/* GET_EVENT is unreliable, use TUR */
+
+	struct cdrom_device_info cdi;
+	struct mutex lock;
+	struct gendisk *disk;
+} Scsi_CD;
+
+#define sr_printk(prefix, cd, fmt, a...) \
+	sdev_prefix_printk(prefix, (cd)->device, (cd)->cdi.name, fmt, ##a)
+
+int sr_do_ioctl(Scsi_CD *, struct packet_command *);
+
+int sr_lock_door(struct cdrom_device_info *, int);
+int sr_tray_move(struct cdrom_device_info *, int);
+int sr_drive_status(struct cdrom_device_info *, int);
+int sr_disk_status(struct cdrom_device_info *);
+int sr_get_last_session(struct cdrom_device_info *, struct cdrom_multisession *);
+int sr_get_mcn(struct cdrom_device_info *, struct cdrom_mcn *);
+int sr_reset(struct cdrom_device_info *);
+int sr_select_speed(struct cdrom_device_info *cdi, unsigned long speed);
+int sr_audio_ioctl(struct cdrom_device_info *, unsigned int, void *);
+
+int sr_is_xa(Scsi_CD *);
+
+/* sr_vendor.c */
+void sr_vendor_init(Scsi_CD *);
+int sr_cd_check(struct cdrom_device_info *);
+int sr_set_blocklength(Scsi_CD *, int blocklength);
+
+#endif