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, 177 insertions, 0 deletions

diff --git a/drivers/usb/host/ehci-grlib.c b/drivers/usb/host/ehci-grlib.c
new file mode 100644
index 000000000..bd9762eaa
--- /dev/null
+++ b/drivers/usb/host/ehci-grlib.c
@@ -0,0 +1,177 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Driver for Aeroflex Gaisler GRLIB GRUSBHC EHCI host controller
+ *
+ * GRUSBHC is typically found on LEON/GRLIB SoCs
+ *
+ * (c) Jan Andersson <jan@gaisler.com>
+ *
+ * Based on ehci-ppc-of.c which is:
+ * (c) Valentine Barshak <vbarshak@ru.mvista.com>
+ * and in turn based on "ehci-ppc-soc.c" by Stefan Roese <sr@denx.de>
+ * and "ohci-ppc-of.c" by Sylvain Munaut <tnt@246tNt.com>
+ */
+
+#include <linux/err.h>
+#include <linux/signal.h>
+
+#include <linux/of_irq.h>
+#include <linux/of_address.h>
+#include <linux/of_platform.h>
+
+#define GRUSBHC_HCIVERSION 0x0100 /* Known value of cap. reg. HCIVERSION */
+
+static const struct hc_driver ehci_grlib_hc_driver = {
+	.description		= hcd_name,
+	.product_desc		= "GRLIB GRUSBHC EHCI",
+	.hcd_priv_size		= sizeof(struct ehci_hcd),
+
+	/*
+	 * generic hardware linkage
+	 */
+	.irq			= ehci_irq,
+	.flags			= HCD_MEMORY | HCD_DMA | HCD_USB2 | HCD_BH,
+
+	/*
+	 * basic lifecycle operations
+	 */
+	.reset			= ehci_setup,
+	.start			= ehci_run,
+	.stop			= ehci_stop,
+	.shutdown		= ehci_shutdown,
+
+	/*
+	 * managing i/o requests and associated device resources
+	 */
+	.urb_enqueue		= ehci_urb_enqueue,
+	.urb_dequeue		= ehci_urb_dequeue,
+	.endpoint_disable	= ehci_endpoint_disable,
+	.endpoint_reset		= ehci_endpoint_reset,
+
+	/*
+	 * scheduling support
+	 */
+	.get_frame_number	= ehci_get_frame,
+
+	/*
+	 * root hub support
+	 */
+	.hub_status_data	= ehci_hub_status_data,
+	.hub_control		= ehci_hub_control,
+#ifdef	CONFIG_PM
+	.bus_suspend		= ehci_bus_suspend,
+	.bus_resume		= ehci_bus_resume,
+#endif
+	.relinquish_port	= ehci_relinquish_port,
+	.port_handed_over	= ehci_port_handed_over,
+
+	.clear_tt_buffer_complete	= ehci_clear_tt_buffer_complete,
+};
+
+
+static int ehci_hcd_grlib_probe(struct platform_device *op)
+{
+	struct device_node *dn = op->dev.of_node;
+	struct usb_hcd *hcd;
+	struct ehci_hcd	*ehci = NULL;
+	struct resource res;
+	u32 hc_capbase;
+	int irq;
+	int rv;
+
+	if (usb_disabled())
+		return -ENODEV;
+
+	dev_dbg(&op->dev, "initializing GRUSBHC EHCI 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(&ehci_grlib_hc_driver, &op->dev,
+			"GRUSBHC EHCI 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) {
+		dev_err(&op->dev, "%s: irq_of_parse_and_map failed\n",
+			__FILE__);
+		rv = -EBUSY;
+		goto err_irq;
+	}
+
+	hcd->regs = devm_ioremap_resource(&op->dev, &res);
+	if (IS_ERR(hcd->regs)) {
+		rv = PTR_ERR(hcd->regs);
+		goto err_ioremap;
+	}
+
+	ehci = hcd_to_ehci(hcd);
+
+	ehci->caps = hcd->regs;
+
+	/* determine endianness of this implementation */
+	hc_capbase = ehci_readl(ehci, &ehci->caps->hc_capbase);
+	if (HC_VERSION(ehci, hc_capbase) != GRUSBHC_HCIVERSION) {
+		ehci->big_endian_mmio = 1;
+		ehci->big_endian_desc = 1;
+		ehci->big_endian_capbase = 1;
+	}
+
+	rv = usb_add_hcd(hcd, irq, 0);
+	if (rv)
+		goto err_ioremap;
+
+	device_wakeup_enable(hcd->self.controller);
+	return 0;
+
+err_ioremap:
+	irq_dispose_mapping(irq);
+err_irq:
+	usb_put_hcd(hcd);
+
+	return rv;
+}
+
+
+static void ehci_hcd_grlib_remove(struct platform_device *op)
+{
+	struct usb_hcd *hcd = platform_get_drvdata(op);
+
+	dev_dbg(&op->dev, "stopping GRLIB GRUSBHC EHCI USB Controller\n");
+
+	usb_remove_hcd(hcd);
+
+	irq_dispose_mapping(hcd->irq);
+
+	usb_put_hcd(hcd);
+}
+
+
+static const struct of_device_id ehci_hcd_grlib_of_match[] = {
+	{
+		.name = "GAISLER_EHCI",
+	 },
+	{
+		.name = "01_026",
+	 },
+	{},
+};
+MODULE_DEVICE_TABLE(of, ehci_hcd_grlib_of_match);
+
+
+static struct platform_driver ehci_grlib_driver = {
+	.probe		= ehci_hcd_grlib_probe,
+	.remove		= ehci_hcd_grlib_remove,
+	.shutdown	= usb_hcd_platform_shutdown,
+	.driver = {
+		.name = "grlib-ehci",
+		.of_match_table = ehci_hcd_grlib_of_match,
+	},
+};