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, 171 insertions, 0 deletions

diff --git a/drivers/phy/broadcom/phy-brcm-usb-init.h b/drivers/phy/broadcom/phy-brcm-usb-init.h
new file mode 100644
index 000000000..4c7be78d0
--- /dev/null
+++ b/drivers/phy/broadcom/phy-brcm-usb-init.h
@@ -0,0 +1,171 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2014-2017 Broadcom
+ */
+
+#ifndef _USB_BRCM_COMMON_INIT_H
+#define _USB_BRCM_COMMON_INIT_H
+
+#include <linux/regmap.h>
+
+#define USB_CTLR_MODE_HOST 0
+#define USB_CTLR_MODE_DEVICE 1
+#define USB_CTLR_MODE_DRD 2
+#define USB_CTLR_MODE_TYPEC_PD 3
+
+enum brcmusb_reg_sel {
+	BRCM_REGS_CTRL = 0,
+	BRCM_REGS_XHCI_EC,
+	BRCM_REGS_XHCI_GBL,
+	BRCM_REGS_USB_PHY,
+	BRCM_REGS_USB_MDIO,
+	BRCM_REGS_BDC_EC,
+	BRCM_REGS_MAX
+};
+
+#define USB_CTRL_REG(base, reg)	((void __iomem *)base + USB_CTRL_##reg)
+#define USB_XHCI_EC_REG(base, reg) ((void __iomem *)base + USB_XHCI_EC_##reg)
+#define USB_CTRL_MASK(reg, field) \
+	USB_CTRL_##reg##_##field##_MASK
+#define USB_CTRL_SET(base, reg, field)	\
+	brcm_usb_ctrl_set(USB_CTRL_REG(base, reg),	\
+			  USB_CTRL_##reg##_##field##_MASK)
+#define USB_CTRL_UNSET(base, reg, field)	\
+	brcm_usb_ctrl_unset(USB_CTRL_REG(base, reg),		\
+			    USB_CTRL_##reg##_##field##_MASK)
+
+#define USB_XHCI_GBL_REG(base, reg) ((void __iomem *)base + USB_XHCI_GBL_##reg)
+#define USB_XHCI_GBL_SET(base, reg, field) \
+	brcm_usb_ctrl_set(USB_XHCI_GBL_REG(base, reg), \
+			  USB_XHCI_GBL_##reg##_##field##_MASK)
+#define USB_XHCI_GBL_UNSET(base, reg, field) \
+	brcm_usb_ctrl_unset(USB_XHCI_GBL_REG(base, reg), \
+			    USB_XHCI_GBL_##reg##_##field##_MASK)
+
+struct  brcm_usb_init_params;
+
+struct brcm_usb_init_ops {
+	void (*init_ipp)(struct brcm_usb_init_params *params);
+	void (*init_common)(struct brcm_usb_init_params *params);
+	void (*init_eohci)(struct brcm_usb_init_params *params);
+	void (*init_xhci)(struct brcm_usb_init_params *params);
+	void (*uninit_common)(struct brcm_usb_init_params *params);
+	void (*uninit_eohci)(struct brcm_usb_init_params *params);
+	void (*uninit_xhci)(struct brcm_usb_init_params *params);
+	int  (*get_dual_select)(struct brcm_usb_init_params *params);
+	void (*set_dual_select)(struct brcm_usb_init_params *params);
+};
+
+struct  brcm_usb_init_params {
+	void __iomem *regs[BRCM_REGS_MAX];
+	int ioc;
+	int ipp;
+	int supported_port_modes;
+	int port_mode;
+	u32 family_id;
+	u32 product_id;
+	int selected_family;
+	const char *family_name;
+	const u32 *usb_reg_bits_map;
+	const struct brcm_usb_init_ops *ops;
+	struct regmap *syscon_piarbctl;
+	bool wake_enabled;
+};
+
+void brcm_usb_dvr_init_74110(struct brcm_usb_init_params *params);
+void brcm_usb_dvr_init_4908(struct brcm_usb_init_params *params);
+void brcm_usb_dvr_init_7445(struct brcm_usb_init_params *params);
+void brcm_usb_dvr_init_7216(struct brcm_usb_init_params *params);
+void brcm_usb_dvr_init_7211b0(struct brcm_usb_init_params *params);
+
+static inline u32 brcm_usb_readl(void __iomem *addr)
+{
+	/*
+	 * MIPS endianness is configured by boot strap, which also reverses all
+	 * bus endianness (i.e., big-endian CPU + big endian bus ==> native
+	 * endian I/O).
+	 *
+	 * Other architectures (e.g., ARM) either do not support big endian, or
+	 * else leave I/O in little endian mode.
+	 */
+	if (IS_ENABLED(CONFIG_MIPS) && IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
+		return __raw_readl(addr);
+	else
+		return readl_relaxed(addr);
+}
+
+static inline void brcm_usb_writel(u32 val, void __iomem *addr)
+{
+	/* See brcmnand_readl() comments */
+	if (IS_ENABLED(CONFIG_MIPS) && IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
+		__raw_writel(val, addr);
+	else
+		writel_relaxed(val, addr);
+}
+
+static inline void brcm_usb_ctrl_unset(void __iomem *reg, u32 mask)
+{
+	brcm_usb_writel(brcm_usb_readl(reg) & ~(mask), reg);
+};
+
+static inline void brcm_usb_ctrl_set(void __iomem *reg, u32 mask)
+{
+	brcm_usb_writel(brcm_usb_readl(reg) | (mask), reg);
+};
+
+static inline void brcm_usb_init_ipp(struct brcm_usb_init_params *ini)
+{
+	if (ini->ops->init_ipp)
+		ini->ops->init_ipp(ini);
+}
+
+static inline void brcm_usb_init_common(struct brcm_usb_init_params *ini)
+{
+	if (ini->ops->init_common)
+		ini->ops->init_common(ini);
+}
+
+static inline void brcm_usb_init_eohci(struct brcm_usb_init_params *ini)
+{
+	if (ini->ops->init_eohci)
+		ini->ops->init_eohci(ini);
+}
+
+static inline void brcm_usb_init_xhci(struct brcm_usb_init_params *ini)
+{
+	if (ini->ops->init_xhci)
+		ini->ops->init_xhci(ini);
+}
+
+static inline void brcm_usb_uninit_common(struct brcm_usb_init_params *ini)
+{
+	if (ini->ops->uninit_common)
+		ini->ops->uninit_common(ini);
+}
+
+static inline void brcm_usb_uninit_eohci(struct brcm_usb_init_params *ini)
+{
+	if (ini->ops->uninit_eohci)
+		ini->ops->uninit_eohci(ini);
+}
+
+static inline void brcm_usb_uninit_xhci(struct brcm_usb_init_params *ini)
+{
+	if (ini->ops->uninit_xhci)
+		ini->ops->uninit_xhci(ini);
+}
+
+static inline int brcm_usb_get_dual_select(struct brcm_usb_init_params *ini)
+{
+	if (ini->ops->get_dual_select)
+		return ini->ops->get_dual_select(ini);
+	return 0;
+}
+
+static inline void brcm_usb_set_dual_select(struct brcm_usb_init_params *ini)
+{
+	if (ini->ops->set_dual_select)
+		ini->ops->set_dual_select(ini);
+}
+
+#endif /* _USB_BRCM_COMMON_INIT_H */