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, 193 insertions, 0 deletions

diff --git a/drivers/usb/host/uhci-grlib.c b/drivers/usb/host/uhci-grlib.c
new file mode 100644
index 000000000..8a1f6d1b5
--- /dev/null
+++ b/drivers/usb/host/uhci-grlib.c
@@ -0,0 +1,193 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * UHCI HCD (Host Controller Driver) for GRLIB GRUSBHC
+ *
+ * Copyright (c) 2011 Jan Andersson <jan@gaisler.com>
+ *
+ * This file is based on UHCI PCI HCD:
+ * (C) Copyright 1999 Linus Torvalds
+ * (C) Copyright 1999-2002 Johannes Erdfelt, johannes@erdfelt.com
+ * (C) Copyright 1999 Randy Dunlap
+ * (C) Copyright 1999 Georg Acher, acher@in.tum.de
+ * (C) Copyright 1999 Deti Fliegl, deti@fliegl.de
+ * (C) Copyright 1999 Thomas Sailer, sailer@ife.ee.ethz.ch
+ * (C) Copyright 1999 Roman Weissgaerber, weissg@vienna.at
+ * (C) Copyright 2000 Yggdrasil Computing, Inc. (port of new PCI interface
+ *               support from usb-ohci.c by Adam Richter, adam@yggdrasil.com).
+ * (C) Copyright 1999 Gregory P. Smith (from usb-ohci.c)
+ * (C) Copyright 2004-2007 Alan Stern, stern@rowland.harvard.edu
+ */
+
+#include <linux/device.h>
+#include <linux/of_irq.h>
+#include <linux/of_address.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+
+static int uhci_grlib_init(struct usb_hcd *hcd)
+{
+	struct uhci_hcd *uhci = hcd_to_uhci(hcd);
+
+	/*
+	 * Probe to determine the endianness of the controller.
+	 * We know that bit 7 of the PORTSC1 register is always set
+	 * and bit 15 is always clear.  If uhci_readw() yields a value
+	 * with bit 7 (0x80) turned on then the current little-endian
+	 * setting is correct.  Otherwise we assume the value was
+	 * byte-swapped; hence the register interface and presumably
+	 * also the descriptors are big-endian.
+	 */
+	if (!(uhci_readw(uhci, USBPORTSC1) & 0x80)) {
+		uhci->big_endian_mmio = 1;
+		uhci->big_endian_desc = 1;
+	}
+
+	uhci->rh_numports = uhci_count_ports(hcd);
+
+	/* Set up pointers to generic functions */
+	uhci->reset_hc = uhci_generic_reset_hc;
+	uhci->check_and_reset_hc = uhci_generic_check_and_reset_hc;
+	/* No special actions need to be taken for the functions below */
+	uhci->configure_hc = NULL;
+	uhci->resume_detect_interrupts_are_broken = NULL;
+	uhci->global_suspend_mode_is_broken = NULL;
+
+	/* Reset if the controller isn't already safely quiescent. */
+	check_and_reset_hc(uhci);
+	return 0;
+}
+
+static const struct hc_driver uhci_grlib_hc_driver = {
+	.description =		hcd_name,
+	.product_desc =		"GRLIB GRUSBHC UHCI Host Controller",
+	.hcd_priv_size =	sizeof(struct uhci_hcd),
+
+	/* Generic hardware linkage */
+	.irq =			uhci_irq,
+	.flags =		HCD_MEMORY | HCD_DMA | HCD_USB11,
+
+	/* Basic lifecycle operations */
+	.reset =		uhci_grlib_init,
+	.start =		uhci_start,
+#ifdef CONFIG_PM
+	.pci_suspend =		NULL,
+	.pci_resume =		NULL,
+	.bus_suspend =		uhci_rh_suspend,
+	.bus_resume =		uhci_rh_resume,
+#endif
+	.stop =			uhci_stop,
+
+	.urb_enqueue =		uhci_urb_enqueue,
+	.urb_dequeue =		uhci_urb_dequeue,
+
+	.endpoint_disable =	uhci_hcd_endpoint_disable,
+	.get_frame_number =	uhci_hcd_get_frame_number,
+
+	.hub_status_data =	uhci_hub_status_data,
+	.hub_control =		uhci_hub_control,
+};
+
+
+static int uhci_hcd_grlib_probe(struct platform_device *op)
+{
+	struct device_node *dn = op->dev.of_node;
+	struct usb_hcd *hcd;
+	struct uhci_hcd	*uhci = NULL;
+	struct resource res;
+	int irq;
+	int rv;
+
+	if (usb_disabled())
+		return -ENODEV;
+
+	dev_dbg(&op->dev, "initializing GRUSBHC UHCI USB Controller\n");
+
+	rv = of_address_to_resource(dn, 0, &res);
+	if (rv)
+		return rv;
+
+	/* usb_create_hcd requires dma_mask != NULL */
+	op->dev.dma_mask = &op->dev.coherent_dma_mask;
+	hcd = usb_create_hcd(&uhci_grlib_hc_driver, &op->dev,
+			"GRUSBHC UHCI USB");
+	if (!hcd)
+		return -ENOMEM;
+
+	hcd->rsrc_start = res.start;
+	hcd->rsrc_len = resource_size(&res);
+
+	irq = irq_of_parse_and_map(dn, 0);
+	if (!irq) {
+		printk(KERN_ERR "%s: irq_of_parse_and_map failed\n", __FILE__);
+		rv = -EBUSY;
+		goto err_usb;
+	}
+
+	hcd->regs = devm_ioremap_resource(&op->dev, &res);
+	if (IS_ERR(hcd->regs)) {
+		rv = PTR_ERR(hcd->regs);
+		goto err_irq;
+	}
+
+	uhci = hcd_to_uhci(hcd);
+
+	uhci->regs = hcd->regs;
+
+	rv = usb_add_hcd(hcd, irq, 0);
+	if (rv)
+		goto err_irq;
+
+	device_wakeup_enable(hcd->self.controller);
+	return 0;
+
+err_irq:
+	irq_dispose_mapping(irq);
+err_usb:
+	usb_put_hcd(hcd);
+
+	return rv;
+}
+
+static void uhci_hcd_grlib_remove(struct platform_device *op)
+{
+	struct usb_hcd *hcd = platform_get_drvdata(op);
+
+	dev_dbg(&op->dev, "stopping GRLIB GRUSBHC UHCI USB Controller\n");
+
+	usb_remove_hcd(hcd);
+
+	irq_dispose_mapping(hcd->irq);
+	usb_put_hcd(hcd);
+}
+
+/* Make sure the controller is quiescent and that we're not using it
+ * any more.  This is mainly for the benefit of programs which, like kexec,
+ * expect the hardware to be idle: not doing DMA or generating IRQs.
+ *
+ * This routine may be called in a damaged or failing kernel.  Hence we
+ * do not acquire the spinlock before shutting down the controller.
+ */
+static void uhci_hcd_grlib_shutdown(struct platform_device *op)
+{
+	struct usb_hcd *hcd = platform_get_drvdata(op);
+
+	uhci_hc_died(hcd_to_uhci(hcd));
+}
+
+static const struct of_device_id uhci_hcd_grlib_of_match[] = {
+	{ .name = "GAISLER_UHCI", },
+	{ .name = "01_027", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, uhci_hcd_grlib_of_match);
+
+
+static struct platform_driver uhci_grlib_driver = {
+	.probe		= uhci_hcd_grlib_probe,
+	.remove		= uhci_hcd_grlib_remove,
+	.shutdown	= uhci_hcd_grlib_shutdown,
+	.driver = {
+		.name = "grlib-uhci",
+		.of_match_table = uhci_hcd_grlib_of_match,
+	},
+};