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, 358 insertions, 0 deletions

diff --git a/drivers/net/phy/lxt.c b/drivers/net/phy/lxt.c
new file mode 100644
index 000000000..5251a61c8
--- /dev/null
+++ b/drivers/net/phy/lxt.c
@@ -0,0 +1,358 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * drivers/net/phy/lxt.c
+ *
+ * Driver for Intel LXT 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>
+
+/* The Level one LXT970 is used by many boards				     */
+
+#define MII_LXT970_IER       17  /* Interrupt Enable Register */
+
+#define MII_LXT970_IER_IEN	0x0002
+
+#define MII_LXT970_ISR       18  /* Interrupt Status Register */
+
+#define MII_LXT970_IRS_MINT  BIT(15)
+
+#define MII_LXT970_CONFIG    19  /* Configuration Register    */
+
+/* ------------------------------------------------------------------------- */
+/* The Level one LXT971 is used on some of my custom boards                  */
+
+/* register definitions for the 971 */
+#define MII_LXT971_IER		18  /* Interrupt Enable Register */
+#define MII_LXT971_IER_IEN	0x00f2
+
+#define MII_LXT971_ISR		19  /* Interrupt Status Register */
+#define MII_LXT971_ISR_MASK	0x00f0
+
+/* register definitions for the 973 */
+#define MII_LXT973_PCR 16 /* Port Configuration Register */
+#define PCR_FIBER_SELECT 1
+
+MODULE_DESCRIPTION("Intel LXT PHY driver");
+MODULE_AUTHOR("Andy Fleming");
+MODULE_LICENSE("GPL");
+
+static int lxt970_ack_interrupt(struct phy_device *phydev)
+{
+	int err;
+
+	err = phy_read(phydev, MII_BMSR);
+
+	if (err < 0)
+		return err;
+
+	err = phy_read(phydev, MII_LXT970_ISR);
+
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static int lxt970_config_intr(struct phy_device *phydev)
+{
+	int err;
+
+	if (phydev->interrupts == PHY_INTERRUPT_ENABLED) {
+		err = lxt970_ack_interrupt(phydev);
+		if (err)
+			return err;
+
+		err = phy_write(phydev, MII_LXT970_IER, MII_LXT970_IER_IEN);
+	} else {
+		err = phy_write(phydev, MII_LXT970_IER, 0);
+		if (err)
+			return err;
+
+		err = lxt970_ack_interrupt(phydev);
+	}
+
+	return err;
+}
+
+static irqreturn_t lxt970_handle_interrupt(struct phy_device *phydev)
+{
+	int irq_status;
+
+	/* The interrupt status register is cleared by reading BMSR
+	 * followed by MII_LXT970_ISR
+	 */
+	irq_status = phy_read(phydev, MII_BMSR);
+	if (irq_status < 0) {
+		phy_error(phydev);
+		return IRQ_NONE;
+	}
+
+	irq_status = phy_read(phydev, MII_LXT970_ISR);
+	if (irq_status < 0) {
+		phy_error(phydev);
+		return IRQ_NONE;
+	}
+
+	if (!(irq_status & MII_LXT970_IRS_MINT))
+		return IRQ_NONE;
+
+	phy_trigger_machine(phydev);
+
+	return IRQ_HANDLED;
+}
+
+static int lxt970_config_init(struct phy_device *phydev)
+{
+	return phy_write(phydev, MII_LXT970_CONFIG, 0);
+}
+
+
+static int lxt971_ack_interrupt(struct phy_device *phydev)
+{
+	int err = phy_read(phydev, MII_LXT971_ISR);
+
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static int lxt971_config_intr(struct phy_device *phydev)
+{
+	int err;
+
+	if (phydev->interrupts == PHY_INTERRUPT_ENABLED) {
+		err = lxt971_ack_interrupt(phydev);
+		if (err)
+			return err;
+
+		err = phy_write(phydev, MII_LXT971_IER, MII_LXT971_IER_IEN);
+	} else {
+		err = phy_write(phydev, MII_LXT971_IER, 0);
+		if (err)
+			return err;
+
+		err = lxt971_ack_interrupt(phydev);
+	}
+
+	return err;
+}
+
+static irqreturn_t lxt971_handle_interrupt(struct phy_device *phydev)
+{
+	int irq_status;
+
+	irq_status = phy_read(phydev, MII_LXT971_ISR);
+	if (irq_status < 0) {
+		phy_error(phydev);
+		return IRQ_NONE;
+	}
+
+	if (!(irq_status & MII_LXT971_ISR_MASK))
+		return IRQ_NONE;
+
+	phy_trigger_machine(phydev);
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * A2 version of LXT973 chip has an ERRATA: it randomly return the contents
+ * of the previous even register when you read a odd register regularly
+ */
+
+static int lxt973a2_update_link(struct phy_device *phydev)
+{
+	int status;
+	int control;
+	int retry = 8; /* we try 8 times */
+
+	/* Do a fake read */
+	status = phy_read(phydev, MII_BMSR);
+
+	if (status < 0)
+		return status;
+
+	control = phy_read(phydev, MII_BMCR);
+	if (control < 0)
+		return control;
+
+	do {
+		/* Read link and autonegotiation status */
+		status = phy_read(phydev, MII_BMSR);
+	} while (status >= 0 && retry-- && status == control);
+
+	if (status < 0)
+		return status;
+
+	if ((status & BMSR_LSTATUS) == 0)
+		phydev->link = 0;
+	else
+		phydev->link = 1;
+
+	return 0;
+}
+
+static int lxt973a2_read_status(struct phy_device *phydev)
+{
+	int adv;
+	int err;
+	int lpa;
+
+	/* Update the link, but return if there was an error */
+	err = lxt973a2_update_link(phydev);
+	if (err)
+		return err;
+
+	if (AUTONEG_ENABLE == phydev->autoneg) {
+		int retry = 1;
+
+		adv = phy_read(phydev, MII_ADVERTISE);
+
+		if (adv < 0)
+			return adv;
+
+		do {
+			lpa = phy_read(phydev, MII_LPA);
+
+			if (lpa < 0)
+				return lpa;
+
+			/* If both registers are equal, it is suspect but not
+			 * impossible, hence a new try
+			 */
+		} while (lpa == adv && retry--);
+
+		mii_lpa_to_linkmode_lpa_t(phydev->lp_advertising, lpa);
+
+		lpa &= adv;
+
+		phydev->speed = SPEED_10;
+		phydev->duplex = DUPLEX_HALF;
+		phydev->pause = phydev->asym_pause = 0;
+
+		if (lpa & (LPA_100FULL | LPA_100HALF)) {
+			phydev->speed = SPEED_100;
+
+			if (lpa & LPA_100FULL)
+				phydev->duplex = DUPLEX_FULL;
+		} else {
+			if (lpa & LPA_10FULL)
+				phydev->duplex = DUPLEX_FULL;
+		}
+
+		phy_resolve_aneg_pause(phydev);
+	} else {
+		err = genphy_read_status_fixed(phydev);
+		if (err < 0)
+			return err;
+
+		phydev->pause = phydev->asym_pause = 0;
+		linkmode_zero(phydev->lp_advertising);
+	}
+
+	return 0;
+}
+
+static int lxt973_probe(struct phy_device *phydev)
+{
+	int val = phy_read(phydev, MII_LXT973_PCR);
+
+	if (val & PCR_FIBER_SELECT) {
+		/*
+		 * If fiber is selected, then the only correct setting
+		 * is 100Mbps, full duplex, and auto negotiation off.
+		 */
+		val = phy_read(phydev, MII_BMCR);
+		val |= (BMCR_SPEED100 | BMCR_FULLDPLX);
+		val &= ~BMCR_ANENABLE;
+		phy_write(phydev, MII_BMCR, val);
+		/* Remember that the port is in fiber mode. */
+		phydev->priv = lxt973_probe;
+		phydev->port = PORT_FIBRE;
+	} else {
+		phydev->priv = NULL;
+	}
+	return 0;
+}
+
+static int lxt973_config_aneg(struct phy_device *phydev)
+{
+	/* Do nothing if port is in fiber mode. */
+	return phydev->priv ? 0 : genphy_config_aneg(phydev);
+}
+
+static struct phy_driver lxt97x_driver[] = {
+{
+	.phy_id		= 0x78100000,
+	.name		= "LXT970",
+	.phy_id_mask	= 0xfffffff0,
+	/* PHY_BASIC_FEATURES */
+	.config_init	= lxt970_config_init,
+	.config_intr	= lxt970_config_intr,
+	.handle_interrupt = lxt970_handle_interrupt,
+}, {
+	.phy_id		= 0x001378e0,
+	.name		= "LXT971",
+	.phy_id_mask	= 0xfffffff0,
+	/* PHY_BASIC_FEATURES */
+	.config_intr	= lxt971_config_intr,
+	.handle_interrupt = lxt971_handle_interrupt,
+	.suspend	= genphy_suspend,
+	.resume		= genphy_resume,
+}, {
+	.phy_id		= 0x00137a10,
+	.name		= "LXT973-A2",
+	.phy_id_mask	= 0xffffffff,
+	/* PHY_BASIC_FEATURES */
+	.flags		= 0,
+	.probe		= lxt973_probe,
+	.config_aneg	= lxt973_config_aneg,
+	.read_status	= lxt973a2_read_status,
+	.suspend	= genphy_suspend,
+	.resume		= genphy_resume,
+}, {
+	.phy_id		= 0x00137a10,
+	.name		= "LXT973",
+	.phy_id_mask	= 0xfffffff0,
+	/* PHY_BASIC_FEATURES */
+	.flags		= 0,
+	.probe		= lxt973_probe,
+	.config_aneg	= lxt973_config_aneg,
+	.suspend	= genphy_suspend,
+	.resume		= genphy_resume,
+} };
+
+module_phy_driver(lxt97x_driver);
+
+static const struct mdio_device_id __maybe_unused lxt_tbl[] = {
+	{ 0x78100000, 0xfffffff0 },
+	{ 0x001378e0, 0xfffffff0 },
+	{ 0x00137a10, 0xfffffff0 },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(mdio, lxt_tbl);