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, 100 insertions, 0 deletions

diff --git a/drivers/usb/chipidea/udc.h b/drivers/usb/chipidea/udc.h
new file mode 100644
index 000000000..c8a47389a
--- /dev/null
+++ b/drivers/usb/chipidea/udc.h
@@ -0,0 +1,100 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * udc.h - ChipIdea UDC structures
+ *
+ * Copyright (C) 2008 Chipidea - MIPS Technologies, Inc. All rights reserved.
+ *
+ * Author: David Lopo
+ */
+
+#ifndef __DRIVERS_USB_CHIPIDEA_UDC_H
+#define __DRIVERS_USB_CHIPIDEA_UDC_H
+
+#include <linux/list.h>
+
+#define CTRL_PAYLOAD_MAX   64
+#define RX        0  /* similar to USB_DIR_OUT but can be used as an index */
+#define TX        1  /* similar to USB_DIR_IN  but can be used as an index */
+
+/* DMA layout of transfer descriptors */
+struct ci_hw_td {
+	/* 0 */
+	__le32 next;
+#define TD_TERMINATE          BIT(0)
+#define TD_ADDR_MASK          (0xFFFFFFEUL << 5)
+	/* 1 */
+	__le32 token;
+#define TD_STATUS             (0x00FFUL <<  0)
+#define TD_STATUS_TR_ERR      BIT(3)
+#define TD_STATUS_DT_ERR      BIT(5)
+#define TD_STATUS_HALTED      BIT(6)
+#define TD_STATUS_ACTIVE      BIT(7)
+#define TD_MULTO              (0x0003UL << 10)
+#define TD_IOC                BIT(15)
+#define TD_TOTAL_BYTES        (0x7FFFUL << 16)
+	/* 2 */
+	__le32 page[5];
+#define TD_CURR_OFFSET        (0x0FFFUL <<  0)
+#define TD_FRAME_NUM          (0x07FFUL <<  0)
+#define TD_RESERVED_MASK      (0x0FFFUL <<  0)
+} __attribute__ ((packed, aligned(4)));
+
+/* DMA layout of queue heads */
+struct ci_hw_qh {
+	/* 0 */
+	__le32 cap;
+#define QH_IOS                BIT(15)
+#define QH_MAX_PKT            (0x07FFUL << 16)
+#define QH_ZLT                BIT(29)
+#define QH_MULT               (0x0003UL << 30)
+#define QH_ISO_MULT(x)		((x >> 11) & 0x03)
+	/* 1 */
+	__le32 curr;
+	/* 2 - 8 */
+	struct ci_hw_td		td;
+	/* 9 */
+	__le32 RESERVED;
+	struct usb_ctrlrequest   setup;
+} __attribute__ ((packed, aligned(4)));
+
+struct td_node {
+	struct list_head	td;
+	dma_addr_t		dma;
+	struct ci_hw_td		*ptr;
+	int			td_remaining_size;
+};
+
+/**
+ * struct ci_hw_req - usb request representation
+ * @req: request structure for gadget drivers
+ * @queue: link to QH list
+ * @tds: link to TD list
+ * @sgt: hold original sglist when bounce sglist
+ */
+struct ci_hw_req {
+	struct usb_request	req;
+	struct list_head	queue;
+	struct list_head	tds;
+	struct sg_table		sgt;
+};
+
+#ifdef CONFIG_USB_CHIPIDEA_UDC
+
+int ci_hdrc_gadget_init(struct ci_hdrc *ci);
+void ci_hdrc_gadget_destroy(struct ci_hdrc *ci);
+
+#else
+
+static inline int ci_hdrc_gadget_init(struct ci_hdrc *ci)
+{
+	return -ENXIO;
+}
+
+static inline void ci_hdrc_gadget_destroy(struct ci_hdrc *ci)
+{
+
+}
+
+#endif
+
+#endif /* __DRIVERS_USB_CHIPIDEA_UDC_H */