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, 163 insertions, 0 deletions

diff --git a/drivers/net/phy/qsemi.c b/drivers/net/phy/qsemi.c
new file mode 100644
index 000000000..7b70ba6ca
--- /dev/null
+++ b/drivers/net/phy/qsemi.c
@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * drivers/net/phy/qsemi.c
+ *
+ * Driver for Quality Semiconductor 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 Quality Semiconductor QS6612 is used on the RPX CLLF                  */
+
+/* register definitions */
+
+#define MII_QS6612_MCR		17  /* Mode Control Register      */
+#define MII_QS6612_FTR		27  /* Factory Test Register      */
+#define MII_QS6612_MCO		28  /* Misc. Control Register     */
+#define MII_QS6612_ISR		29  /* Interrupt Source Register  */
+#define MII_QS6612_IMR		30  /* Interrupt Mask Register    */
+#define MII_QS6612_IMR_INIT	0x003a
+#define MII_QS6612_PCR		31  /* 100BaseTx PHY Control Reg. */
+
+#define QS6612_PCR_AN_COMPLETE	0x1000
+#define QS6612_PCR_RLBEN	0x0200
+#define QS6612_PCR_DCREN	0x0100
+#define QS6612_PCR_4B5BEN	0x0040
+#define QS6612_PCR_TX_ISOLATE	0x0020
+#define QS6612_PCR_MLT3_DIS	0x0002
+#define QS6612_PCR_SCRM_DESCRM	0x0001
+
+MODULE_DESCRIPTION("Quality Semiconductor PHY driver");
+MODULE_AUTHOR("Andy Fleming");
+MODULE_LICENSE("GPL");
+
+/* Returns 0, unless there's a write error */
+static int qs6612_config_init(struct phy_device *phydev)
+{
+	/* The PHY powers up isolated on the RPX,
+	 * so send a command to allow operation.
+	 * XXX - My docs indicate this should be 0x0940
+	 * ...or something.  The current value sets three
+	 * reserved bits, bit 11, which specifies it should be
+	 * set to one, bit 10, which specifies it should be set
+	 * to 0, and bit 7, which doesn't specify.  However, my
+	 * docs are preliminary, and I will leave it like this
+	 * until someone more knowledgable corrects me or it.
+	 * -- Andy Fleming
+	 */
+	return phy_write(phydev, MII_QS6612_PCR, 0x0dc0);
+}
+
+static int qs6612_ack_interrupt(struct phy_device *phydev)
+{
+	int err;
+
+	/* The Interrupt Source register is not self-clearing, bits 4 and 5 are
+	 * cleared when MII_BMSR is read and bits 1 and 3 are cleared when
+	 * MII_EXPANSION is read
+	 */
+	err = phy_read(phydev, MII_QS6612_ISR);
+
+	if (err < 0)
+		return err;
+
+	err = phy_read(phydev, MII_BMSR);
+
+	if (err < 0)
+		return err;
+
+	err = phy_read(phydev, MII_EXPANSION);
+
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static int qs6612_config_intr(struct phy_device *phydev)
+{
+	int err;
+
+	if (phydev->interrupts == PHY_INTERRUPT_ENABLED) {
+		/* clear any interrupts before enabling them */
+		err = qs6612_ack_interrupt(phydev);
+		if (err)
+			return err;
+
+		err = phy_write(phydev, MII_QS6612_IMR,
+				MII_QS6612_IMR_INIT);
+	} else {
+		err = phy_write(phydev, MII_QS6612_IMR, 0);
+		if (err)
+			return err;
+
+		/* clear any leftover interrupts */
+		err = qs6612_ack_interrupt(phydev);
+	}
+
+	return err;
+
+}
+
+static irqreturn_t qs6612_handle_interrupt(struct phy_device *phydev)
+{
+	int irq_status;
+
+	irq_status = phy_read(phydev, MII_QS6612_ISR);
+	if (irq_status < 0) {
+		phy_error(phydev);
+		return IRQ_NONE;
+	}
+
+	if (!(irq_status & MII_QS6612_IMR_INIT))
+		return IRQ_NONE;
+
+	/* the interrupt source register is not self-clearing */
+	qs6612_ack_interrupt(phydev);
+
+	phy_trigger_machine(phydev);
+
+	return IRQ_HANDLED;
+}
+
+static struct phy_driver qs6612_driver[] = { {
+	.phy_id		= 0x00181440,
+	.name		= "QS6612",
+	.phy_id_mask	= 0xfffffff0,
+	/* PHY_BASIC_FEATURES */
+	.config_init	= qs6612_config_init,
+	.config_intr	= qs6612_config_intr,
+	.handle_interrupt = qs6612_handle_interrupt,
+} };
+
+module_phy_driver(qs6612_driver);
+
+static const struct mdio_device_id __maybe_unused qs6612_tbl[] = {
+	{ 0x00181440, 0xfffffff0 },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(mdio, qs6612_tbl);