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, 220 insertions, 0 deletions

diff --git a/drivers/net/phy/davicom.c b/drivers/net/phy/davicom.c
new file mode 100644
index 000000000..fa3692508
--- /dev/null
+++ b/drivers/net/phy/davicom.c
@@ -0,0 +1,220 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * drivers/net/phy/davicom.c
+ *
+ * Driver for Davicom PHYs
+ *
+ * Author: Andy Fleming
+ *
+ * Copyright (c) 2004 Freescale Semiconductor, Inc.
+ */
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/unistd.h>
+#include <linux/interrupt.h>
+#include <linux/init.h>
+#include <linux/delay.h>
+#include <linux/netdevice.h>
+#include <linux/etherdevice.h>
+#include <linux/skbuff.h>
+#include <linux/spinlock.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/mii.h>
+#include <linux/ethtool.h>
+#include <linux/phy.h>
+
+#include <asm/io.h>
+#include <asm/irq.h>
+#include <linux/uaccess.h>
+
+#define MII_DM9161_SCR		0x10
+#define MII_DM9161_SCR_INIT	0x0610
+#define MII_DM9161_SCR_RMII	0x0100
+
+/* DM9161 Interrupt Register */
+#define MII_DM9161_INTR	0x15
+#define MII_DM9161_INTR_PEND		0x8000
+#define MII_DM9161_INTR_DPLX_MASK	0x0800
+#define MII_DM9161_INTR_SPD_MASK	0x0400
+#define MII_DM9161_INTR_LINK_MASK	0x0200
+#define MII_DM9161_INTR_MASK		0x0100
+#define MII_DM9161_INTR_DPLX_CHANGE	0x0010
+#define MII_DM9161_INTR_SPD_CHANGE	0x0008
+#define MII_DM9161_INTR_LINK_CHANGE	0x0004
+#define MII_DM9161_INTR_INIT		0x0000
+#define MII_DM9161_INTR_STOP	\
+	(MII_DM9161_INTR_DPLX_MASK | MII_DM9161_INTR_SPD_MASK |	\
+	 MII_DM9161_INTR_LINK_MASK | MII_DM9161_INTR_MASK)
+#define MII_DM9161_INTR_CHANGE	\
+	(MII_DM9161_INTR_DPLX_CHANGE | \
+	 MII_DM9161_INTR_SPD_CHANGE | \
+	 MII_DM9161_INTR_LINK_CHANGE)
+
+/* DM9161 10BT Configuration/Status */
+#define MII_DM9161_10BTCSR	0x12
+#define MII_DM9161_10BTCSR_INIT	0x7800
+
+MODULE_DESCRIPTION("Davicom PHY driver");
+MODULE_AUTHOR("Andy Fleming");
+MODULE_LICENSE("GPL");
+
+
+static int dm9161_ack_interrupt(struct phy_device *phydev)
+{
+	int err = phy_read(phydev, MII_DM9161_INTR);
+
+	return (err < 0) ? err : 0;
+}
+
+#define DM9161_DELAY 1
+static int dm9161_config_intr(struct phy_device *phydev)
+{
+	int temp, err;
+
+	temp = phy_read(phydev, MII_DM9161_INTR);
+
+	if (temp < 0)
+		return temp;
+
+	if (phydev->interrupts == PHY_INTERRUPT_ENABLED) {
+		err = dm9161_ack_interrupt(phydev);
+		if (err)
+			return err;
+
+		temp &= ~(MII_DM9161_INTR_STOP);
+		err = phy_write(phydev, MII_DM9161_INTR, temp);
+	} else {
+		temp |= MII_DM9161_INTR_STOP;
+		err = phy_write(phydev, MII_DM9161_INTR, temp);
+		if (err)
+			return err;
+
+		err = dm9161_ack_interrupt(phydev);
+	}
+
+	return err;
+}
+
+static irqreturn_t dm9161_handle_interrupt(struct phy_device *phydev)
+{
+	int irq_status;
+
+	irq_status = phy_read(phydev, MII_DM9161_INTR);
+	if (irq_status < 0) {
+		phy_error(phydev);
+		return IRQ_NONE;
+	}
+
+	if (!(irq_status & MII_DM9161_INTR_CHANGE))
+		return IRQ_NONE;
+
+	phy_trigger_machine(phydev);
+
+	return IRQ_HANDLED;
+}
+
+static int dm9161_config_aneg(struct phy_device *phydev)
+{
+	int err;
+
+	/* Isolate the PHY */
+	err = phy_write(phydev, MII_BMCR, BMCR_ISOLATE);
+
+	if (err < 0)
+		return err;
+
+	/* Configure the new settings */
+	err = genphy_config_aneg(phydev);
+
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static int dm9161_config_init(struct phy_device *phydev)
+{
+	int err, temp;
+
+	/* Isolate the PHY */
+	err = phy_write(phydev, MII_BMCR, BMCR_ISOLATE);
+
+	if (err < 0)
+		return err;
+
+	switch (phydev->interface) {
+	case PHY_INTERFACE_MODE_MII:
+		temp = MII_DM9161_SCR_INIT;
+		break;
+	case PHY_INTERFACE_MODE_RMII:
+		temp =  MII_DM9161_SCR_INIT | MII_DM9161_SCR_RMII;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Do not bypass the scrambler/descrambler */
+	err = phy_write(phydev, MII_DM9161_SCR, temp);
+	if (err < 0)
+		return err;
+
+	/* Clear 10BTCSR to default */
+	err = phy_write(phydev, MII_DM9161_10BTCSR, MII_DM9161_10BTCSR_INIT);
+
+	if (err < 0)
+		return err;
+
+	/* Reconnect the PHY, and enable Autonegotiation */
+	return phy_write(phydev, MII_BMCR, BMCR_ANENABLE);
+}
+
+static struct phy_driver dm91xx_driver[] = {
+{
+	.phy_id		= 0x0181b880,
+	.name		= "Davicom DM9161E",
+	.phy_id_mask	= 0x0ffffff0,
+	/* PHY_BASIC_FEATURES */
+	.config_init	= dm9161_config_init,
+	.config_aneg	= dm9161_config_aneg,
+	.config_intr	= dm9161_config_intr,
+	.handle_interrupt = dm9161_handle_interrupt,
+}, {
+	.phy_id		= 0x0181b8b0,
+	.name		= "Davicom DM9161B/C",
+	.phy_id_mask	= 0x0ffffff0,
+	/* PHY_BASIC_FEATURES */
+	.config_init	= dm9161_config_init,
+	.config_aneg	= dm9161_config_aneg,
+	.config_intr	= dm9161_config_intr,
+	.handle_interrupt = dm9161_handle_interrupt,
+}, {
+	.phy_id		= 0x0181b8a0,
+	.name		= "Davicom DM9161A",
+	.phy_id_mask	= 0x0ffffff0,
+	/* PHY_BASIC_FEATURES */
+	.config_init	= dm9161_config_init,
+	.config_aneg	= dm9161_config_aneg,
+	.config_intr	= dm9161_config_intr,
+	.handle_interrupt = dm9161_handle_interrupt,
+}, {
+	.phy_id		= 0x00181b80,
+	.name		= "Davicom DM9131",
+	.phy_id_mask	= 0x0ffffff0,
+	/* PHY_BASIC_FEATURES */
+	.config_intr	= dm9161_config_intr,
+	.handle_interrupt = dm9161_handle_interrupt,
+} };
+
+module_phy_driver(dm91xx_driver);
+
+static const struct mdio_device_id __maybe_unused davicom_tbl[] = {
+	{ 0x0181b880, 0x0ffffff0 },
+	{ 0x0181b8b0, 0x0ffffff0 },
+	{ 0x0181b8a0, 0x0ffffff0 },
+	{ 0x00181b80, 0x0ffffff0 },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(mdio, davicom_tbl);