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, 137 insertions, 0 deletions

diff --git a/drivers/net/phy/ste10Xp.c b/drivers/net/phy/ste10Xp.c
new file mode 100644
index 000000000..d4835d4c5
--- /dev/null
+++ b/drivers/net/phy/ste10Xp.c
@@ -0,0 +1,137 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * drivers/net/phy/ste10Xp.c
+ *
+ * Driver for STMicroelectronics STe10Xp PHYs
+ *
+ * Author: Giuseppe Cavallaro <peppe.cavallaro@st.com>
+ *
+ * Copyright (c) 2008 STMicroelectronics Limited
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <linux/moduleparam.h>
+#include <linux/interrupt.h>
+#include <linux/netdevice.h>
+#include <linux/ethtool.h>
+#include <linux/mii.h>
+#include <linux/phy.h>
+
+#define MII_XCIIS	0x11	/* Configuration Info IRQ & Status Reg */
+#define MII_XIE		0x12	/* Interrupt Enable Register */
+#define MII_XIE_DEFAULT_MASK 0x0070 /* ANE complete, Remote Fault, Link Down */
+
+#define STE101P_PHY_ID		0x00061c50
+#define STE100P_PHY_ID		0x1c040011
+
+static int ste10Xp_config_init(struct phy_device *phydev)
+{
+	int value, err;
+
+	/* Software Reset PHY */
+	value = phy_read(phydev, MII_BMCR);
+	if (value < 0)
+		return value;
+
+	value |= BMCR_RESET;
+	err = phy_write(phydev, MII_BMCR, value);
+	if (err < 0)
+		return err;
+
+	do {
+		value = phy_read(phydev, MII_BMCR);
+	} while (value & BMCR_RESET);
+
+	return 0;
+}
+
+static int ste10Xp_ack_interrupt(struct phy_device *phydev)
+{
+	int err = phy_read(phydev, MII_XCIIS);
+
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+static int ste10Xp_config_intr(struct phy_device *phydev)
+{
+	int err;
+
+	if (phydev->interrupts == PHY_INTERRUPT_ENABLED) {
+		/* clear any pending interrupts */
+		err = ste10Xp_ack_interrupt(phydev);
+		if (err)
+			return err;
+
+		/* Enable all STe101P interrupts (PR12) */
+		err = phy_write(phydev, MII_XIE, MII_XIE_DEFAULT_MASK);
+	} else {
+		err = phy_write(phydev, MII_XIE, 0);
+		if (err)
+			return err;
+
+		err = ste10Xp_ack_interrupt(phydev);
+	}
+
+	return err;
+}
+
+static irqreturn_t ste10Xp_handle_interrupt(struct phy_device *phydev)
+{
+	int irq_status;
+
+	irq_status = phy_read(phydev, MII_XCIIS);
+	if (irq_status < 0) {
+		phy_error(phydev);
+		return IRQ_NONE;
+	}
+
+	if (!(irq_status & MII_XIE_DEFAULT_MASK))
+		return IRQ_NONE;
+
+	phy_trigger_machine(phydev);
+
+	return IRQ_HANDLED;
+}
+
+static struct phy_driver ste10xp_pdriver[] = {
+{
+	.phy_id = STE101P_PHY_ID,
+	.phy_id_mask = 0xfffffff0,
+	.name = "STe101p",
+	/* PHY_BASIC_FEATURES */
+	.config_init = ste10Xp_config_init,
+	.config_intr = ste10Xp_config_intr,
+	.handle_interrupt = ste10Xp_handle_interrupt,
+	.suspend = genphy_suspend,
+	.resume = genphy_resume,
+}, {
+	.phy_id = STE100P_PHY_ID,
+	.phy_id_mask = 0xffffffff,
+	.name = "STe100p",
+	/* PHY_BASIC_FEATURES */
+	.config_init = ste10Xp_config_init,
+	.config_intr = ste10Xp_config_intr,
+	.handle_interrupt = ste10Xp_handle_interrupt,
+	.suspend = genphy_suspend,
+	.resume = genphy_resume,
+} };
+
+module_phy_driver(ste10xp_pdriver);
+
+static const struct mdio_device_id __maybe_unused ste10Xp_tbl[] = {
+	{ STE101P_PHY_ID, 0xfffffff0 },
+	{ STE100P_PHY_ID, 0xffffffff },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(mdio, ste10Xp_tbl);
+
+MODULE_DESCRIPTION("STMicroelectronics STe10Xp PHY driver");
+MODULE_AUTHOR("Giuseppe Cavallaro <peppe.cavallaro@st.com>");
+MODULE_LICENSE("GPL");