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, 348 insertions, 0 deletions

diff --git a/drivers/usb/phy/phy-generic.c b/drivers/usb/phy/phy-generic.c
new file mode 100644
index 000000000..de26b3023
--- /dev/null
+++ b/drivers/usb/phy/phy-generic.c
@@ -0,0 +1,348 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * NOP USB transceiver for all USB transceiver which are either built-in
+ * into USB IP or which are mostly autonomous.
+ *
+ * Copyright (C) 2009 Texas Instruments Inc
+ * Author: Ajay Kumar Gupta <ajay.gupta@ti.com>
+ *
+ * Current status:
+ *	This provides a "nop" transceiver for PHYs which are
+ *	autonomous such as isp1504, isp1707, etc.
+ */
+
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/dma-mapping.h>
+#include <linux/usb/gadget.h>
+#include <linux/usb/otg.h>
+#include <linux/usb/usb_phy_generic.h>
+#include <linux/slab.h>
+#include <linux/clk.h>
+#include <linux/regulator/consumer.h>
+#include <linux/property.h>
+#include <linux/gpio/consumer.h>
+#include <linux/delay.h>
+
+#include "phy-generic.h"
+
+#define VBUS_IRQ_FLAGS \
+	(IRQF_SHARED | IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING | \
+		IRQF_ONESHOT)
+
+struct platform_device *usb_phy_generic_register(void)
+{
+	return platform_device_register_simple("usb_phy_generic",
+			PLATFORM_DEVID_AUTO, NULL, 0);
+}
+EXPORT_SYMBOL_GPL(usb_phy_generic_register);
+
+void usb_phy_generic_unregister(struct platform_device *pdev)
+{
+	platform_device_unregister(pdev);
+}
+EXPORT_SYMBOL_GPL(usb_phy_generic_unregister);
+
+static int nop_set_suspend(struct usb_phy *x, int suspend)
+{
+	struct usb_phy_generic *nop = dev_get_drvdata(x->dev);
+	int ret = 0;
+
+	if (suspend) {
+		clk_disable_unprepare(nop->clk);
+		if (!IS_ERR(nop->vcc) && !device_may_wakeup(x->dev))
+			ret = regulator_disable(nop->vcc);
+	} else {
+		if (!IS_ERR(nop->vcc) && !device_may_wakeup(x->dev))
+			ret = regulator_enable(nop->vcc);
+		clk_prepare_enable(nop->clk);
+	}
+
+	return ret;
+}
+
+static void nop_reset(struct usb_phy_generic *nop)
+{
+	if (!nop->gpiod_reset)
+		return;
+
+	gpiod_set_value_cansleep(nop->gpiod_reset, 1);
+	usleep_range(10000, 20000);
+	gpiod_set_value_cansleep(nop->gpiod_reset, 0);
+	usleep_range(10000, 30000);
+}
+
+/* interface to regulator framework */
+static int nop_set_vbus(struct usb_otg *otg, bool enable)
+{
+	int ret = 0;
+	struct usb_phy_generic *nop = dev_get_drvdata(otg->usb_phy->dev);
+
+	if (!nop->vbus_draw)
+		return 0;
+
+	if (enable && !nop->vbus_draw_enabled) {
+		ret = regulator_enable(nop->vbus_draw);
+		if (ret)
+			nop->vbus_draw_enabled = false;
+		else
+			nop->vbus_draw_enabled = true;
+
+	} else if (!enable && nop->vbus_draw_enabled) {
+		ret = regulator_disable(nop->vbus_draw);
+		nop->vbus_draw_enabled = false;
+	}
+	return ret;
+}
+
+
+static irqreturn_t nop_gpio_vbus_thread(int irq, void *data)
+{
+	struct usb_phy_generic *nop = data;
+	struct usb_otg *otg = nop->phy.otg;
+	int vbus, status;
+
+	vbus = gpiod_get_value(nop->gpiod_vbus);
+	if ((vbus ^ nop->vbus) == 0)
+		return IRQ_HANDLED;
+	nop->vbus = vbus;
+
+	if (vbus) {
+		status = USB_EVENT_VBUS;
+		otg->state = OTG_STATE_B_PERIPHERAL;
+		nop->phy.last_event = status;
+
+		atomic_notifier_call_chain(&nop->phy.notifier, status,
+					   otg->gadget);
+	} else {
+		status = USB_EVENT_NONE;
+		otg->state = OTG_STATE_B_IDLE;
+		nop->phy.last_event = status;
+
+		atomic_notifier_call_chain(&nop->phy.notifier, status,
+					   otg->gadget);
+	}
+	return IRQ_HANDLED;
+}
+
+int usb_gen_phy_init(struct usb_phy *phy)
+{
+	struct usb_phy_generic *nop = dev_get_drvdata(phy->dev);
+	int ret;
+
+	if (!IS_ERR(nop->vcc)) {
+		if (regulator_enable(nop->vcc))
+			dev_err(phy->dev, "Failed to enable power\n");
+	}
+
+	ret = clk_prepare_enable(nop->clk);
+	if (ret)
+		return ret;
+
+	nop_reset(nop);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(usb_gen_phy_init);
+
+void usb_gen_phy_shutdown(struct usb_phy *phy)
+{
+	struct usb_phy_generic *nop = dev_get_drvdata(phy->dev);
+
+	gpiod_set_value_cansleep(nop->gpiod_reset, 1);
+
+	clk_disable_unprepare(nop->clk);
+
+	if (!IS_ERR(nop->vcc)) {
+		if (regulator_disable(nop->vcc))
+			dev_err(phy->dev, "Failed to disable power\n");
+	}
+}
+EXPORT_SYMBOL_GPL(usb_gen_phy_shutdown);
+
+static int nop_set_peripheral(struct usb_otg *otg, struct usb_gadget *gadget)
+{
+	if (!otg)
+		return -ENODEV;
+
+	if (!gadget) {
+		otg->gadget = NULL;
+		return -ENODEV;
+	}
+
+	otg->gadget = gadget;
+	if (otg->state == OTG_STATE_B_PERIPHERAL)
+		atomic_notifier_call_chain(&otg->usb_phy->notifier,
+					   USB_EVENT_VBUS, otg->gadget);
+	else
+		otg->state = OTG_STATE_B_IDLE;
+	return 0;
+}
+
+static int nop_set_host(struct usb_otg *otg, struct usb_bus *host)
+{
+	if (!otg)
+		return -ENODEV;
+
+	if (!host) {
+		otg->host = NULL;
+		return -ENODEV;
+	}
+
+	otg->host = host;
+	return 0;
+}
+
+int usb_phy_gen_create_phy(struct device *dev, struct usb_phy_generic *nop)
+{
+	enum usb_phy_type type = USB_PHY_TYPE_USB2;
+	int err = 0;
+	u32 clk_rate = 0;
+
+	device_property_read_u32(dev, "clock-frequency", &clk_rate);
+	nop->gpiod_reset = devm_gpiod_get_optional(dev, "reset",
+						   GPIOD_ASIS);
+	err = PTR_ERR_OR_ZERO(nop->gpiod_reset);
+	if (!err) {
+		nop->gpiod_vbus = devm_gpiod_get_optional(dev,
+						 "vbus-detect",
+						 GPIOD_ASIS);
+		err = PTR_ERR_OR_ZERO(nop->gpiod_vbus);
+	}
+
+	if (err)
+		return dev_err_probe(dev, err,
+				     "Error requesting RESET or VBUS GPIO\n");
+	if (nop->gpiod_reset)
+		gpiod_direction_output(nop->gpiod_reset, 1);
+
+	nop->phy.otg = devm_kzalloc(dev, sizeof(*nop->phy.otg),
+			GFP_KERNEL);
+	if (!nop->phy.otg)
+		return -ENOMEM;
+
+	nop->clk = devm_clk_get_optional(dev, "main_clk");
+	if (IS_ERR(nop->clk))
+		return dev_err_probe(dev, PTR_ERR(nop->clk),
+				     "Can't get phy clock\n");
+
+	if (clk_rate) {
+		err = clk_set_rate(nop->clk, clk_rate);
+		if (err)
+			return dev_err_probe(dev, err,
+					     "Error setting clock rate\n");
+	}
+
+	nop->vcc = devm_regulator_get_optional(dev, "vcc");
+	if (IS_ERR(nop->vcc) && PTR_ERR(nop->vcc) != -ENODEV)
+		return dev_err_probe(dev, PTR_ERR(nop->vcc),
+				     "could not get vcc regulator\n");
+
+	nop->vbus_draw = devm_regulator_get_exclusive(dev, "vbus");
+	if (PTR_ERR(nop->vbus_draw) == -ENODEV)
+		nop->vbus_draw = NULL;
+	if (IS_ERR(nop->vbus_draw))
+		return dev_err_probe(dev, PTR_ERR(nop->vbus_draw),
+				     "could not get vbus regulator\n");
+
+	nop->dev		= dev;
+	nop->phy.dev		= nop->dev;
+	nop->phy.label		= "nop-xceiv";
+	nop->phy.set_suspend	= nop_set_suspend;
+	nop->phy.type		= type;
+
+	nop->phy.otg->state		= OTG_STATE_UNDEFINED;
+	nop->phy.otg->usb_phy		= &nop->phy;
+	nop->phy.otg->set_host		= nop_set_host;
+	nop->phy.otg->set_peripheral	= nop_set_peripheral;
+	nop->phy.otg->set_vbus          = nop_set_vbus;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(usb_phy_gen_create_phy);
+
+static int usb_phy_generic_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct usb_phy_generic	*nop;
+	int err;
+
+	nop = devm_kzalloc(dev, sizeof(*nop), GFP_KERNEL);
+	if (!nop)
+		return -ENOMEM;
+
+	err = usb_phy_gen_create_phy(dev, nop);
+	if (err)
+		return err;
+
+	if (nop->gpiod_vbus) {
+		err = devm_request_threaded_irq(dev,
+						gpiod_to_irq(nop->gpiod_vbus),
+						NULL, nop_gpio_vbus_thread,
+						VBUS_IRQ_FLAGS, "vbus_detect",
+						nop);
+		if (err)
+			return dev_err_probe(dev, err, "can't request irq %i\n",
+					     gpiod_to_irq(nop->gpiod_vbus));
+
+		nop->phy.otg->state = gpiod_get_value(nop->gpiod_vbus) ?
+			OTG_STATE_B_PERIPHERAL : OTG_STATE_B_IDLE;
+	}
+
+	nop->phy.init		= usb_gen_phy_init;
+	nop->phy.shutdown	= usb_gen_phy_shutdown;
+
+	err = usb_add_phy_dev(&nop->phy);
+	if (err)
+		return dev_err_probe(dev, err, "can't register transceiver\n");
+
+	platform_set_drvdata(pdev, nop);
+
+	device_set_wakeup_capable(dev,
+				  device_property_read_bool(dev, "wakeup-source"));
+
+	return 0;
+}
+
+static void usb_phy_generic_remove(struct platform_device *pdev)
+{
+	struct usb_phy_generic *nop = platform_get_drvdata(pdev);
+
+	usb_remove_phy(&nop->phy);
+
+	if (nop->vbus_draw && nop->vbus_draw_enabled)
+		regulator_disable(nop->vbus_draw);
+}
+
+static const struct of_device_id nop_xceiv_dt_ids[] = {
+	{ .compatible = "usb-nop-xceiv" },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(of, nop_xceiv_dt_ids);
+
+static struct platform_driver usb_phy_generic_driver = {
+	.probe		= usb_phy_generic_probe,
+	.remove		= usb_phy_generic_remove,
+	.driver		= {
+		.name	= "usb_phy_generic",
+		.of_match_table = nop_xceiv_dt_ids,
+	},
+};
+
+static int __init usb_phy_generic_init(void)
+{
+	return platform_driver_register(&usb_phy_generic_driver);
+}
+subsys_initcall(usb_phy_generic_init);
+
+static void __exit usb_phy_generic_exit(void)
+{
+	platform_driver_unregister(&usb_phy_generic_driver);
+}
+module_exit(usb_phy_generic_exit);
+
+MODULE_ALIAS("platform:usb_phy_generic");
+MODULE_AUTHOR("Texas Instruments Inc");
+MODULE_DESCRIPTION("NOP USB Transceiver driver");
+MODULE_LICENSE("GPL");