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, 297 insertions, 0 deletions

diff --git a/drivers/ssb/driver_gige.c b/drivers/ssb/driver_gige.c
new file mode 100644
index 000000000..0aca07118
--- /dev/null
+++ b/drivers/ssb/driver_gige.c
@@ -0,0 +1,297 @@
+/*
+ * Sonics Silicon Backplane
+ * Broadcom Gigabit Ethernet core driver
+ *
+ * Copyright 2008, Broadcom Corporation
+ * Copyright 2008, Michael Buesch <m@bues.ch>
+ *
+ * Licensed under the GNU/GPL. See COPYING for details.
+ */
+
+#include <linux/ssb/ssb.h>
+#include <linux/ssb/ssb_driver_gige.h>
+#include <linux/export.h>
+#include <linux/pci.h>
+#include <linux/pci_regs.h>
+#include <linux/slab.h>
+
+
+/*
+MODULE_DESCRIPTION("SSB Broadcom Gigabit Ethernet driver");
+MODULE_AUTHOR("Michael Buesch");
+MODULE_LICENSE("GPL");
+*/
+
+static const struct ssb_device_id ssb_gige_tbl[] = {
+	SSB_DEVICE(SSB_VENDOR_BROADCOM, SSB_DEV_ETHERNET_GBIT, SSB_ANY_REV),
+	{},
+};
+/* MODULE_DEVICE_TABLE(ssb, ssb_gige_tbl); */
+
+
+static inline u8 gige_read8(struct ssb_gige *dev, u16 offset)
+{
+	return ssb_read8(dev->dev, offset);
+}
+
+static inline u16 gige_read16(struct ssb_gige *dev, u16 offset)
+{
+	return ssb_read16(dev->dev, offset);
+}
+
+static inline u32 gige_read32(struct ssb_gige *dev, u16 offset)
+{
+	return ssb_read32(dev->dev, offset);
+}
+
+static inline void gige_write8(struct ssb_gige *dev,
+			       u16 offset, u8 value)
+{
+	ssb_write8(dev->dev, offset, value);
+}
+
+static inline void gige_write16(struct ssb_gige *dev,
+				u16 offset, u16 value)
+{
+	ssb_write16(dev->dev, offset, value);
+}
+
+static inline void gige_write32(struct ssb_gige *dev,
+				u16 offset, u32 value)
+{
+	ssb_write32(dev->dev, offset, value);
+}
+
+static inline
+u8 gige_pcicfg_read8(struct ssb_gige *dev, unsigned int offset)
+{
+	BUG_ON(offset >= 256);
+	return gige_read8(dev, SSB_GIGE_PCICFG + offset);
+}
+
+static inline
+u16 gige_pcicfg_read16(struct ssb_gige *dev, unsigned int offset)
+{
+	BUG_ON(offset >= 256);
+	return gige_read16(dev, SSB_GIGE_PCICFG + offset);
+}
+
+static inline
+u32 gige_pcicfg_read32(struct ssb_gige *dev, unsigned int offset)
+{
+	BUG_ON(offset >= 256);
+	return gige_read32(dev, SSB_GIGE_PCICFG + offset);
+}
+
+static inline
+void gige_pcicfg_write8(struct ssb_gige *dev,
+			unsigned int offset, u8 value)
+{
+	BUG_ON(offset >= 256);
+	gige_write8(dev, SSB_GIGE_PCICFG + offset, value);
+}
+
+static inline
+void gige_pcicfg_write16(struct ssb_gige *dev,
+			 unsigned int offset, u16 value)
+{
+	BUG_ON(offset >= 256);
+	gige_write16(dev, SSB_GIGE_PCICFG + offset, value);
+}
+
+static inline
+void gige_pcicfg_write32(struct ssb_gige *dev,
+			 unsigned int offset, u32 value)
+{
+	BUG_ON(offset >= 256);
+	gige_write32(dev, SSB_GIGE_PCICFG + offset, value);
+}
+
+static int ssb_gige_pci_read_config(struct pci_bus *bus, unsigned int devfn,
+				    int reg, int size, u32 *val)
+{
+	struct ssb_gige *dev = container_of(bus->ops, struct ssb_gige, pci_ops);
+	unsigned long flags;
+
+	if ((PCI_SLOT(devfn) > 0) || (PCI_FUNC(devfn) > 0))
+		return PCIBIOS_DEVICE_NOT_FOUND;
+	if (reg >= 256)
+		return PCIBIOS_DEVICE_NOT_FOUND;
+
+	spin_lock_irqsave(&dev->lock, flags);
+	switch (size) {
+	case 1:
+		*val = gige_pcicfg_read8(dev, reg);
+		break;
+	case 2:
+		*val = gige_pcicfg_read16(dev, reg);
+		break;
+	case 4:
+		*val = gige_pcicfg_read32(dev, reg);
+		break;
+	default:
+		WARN_ON(1);
+	}
+	spin_unlock_irqrestore(&dev->lock, flags);
+
+	return PCIBIOS_SUCCESSFUL;
+}
+
+static int ssb_gige_pci_write_config(struct pci_bus *bus, unsigned int devfn,
+				     int reg, int size, u32 val)
+{
+	struct ssb_gige *dev = container_of(bus->ops, struct ssb_gige, pci_ops);
+	unsigned long flags;
+
+	if ((PCI_SLOT(devfn) > 0) || (PCI_FUNC(devfn) > 0))
+		return PCIBIOS_DEVICE_NOT_FOUND;
+	if (reg >= 256)
+		return PCIBIOS_DEVICE_NOT_FOUND;
+
+	spin_lock_irqsave(&dev->lock, flags);
+	switch (size) {
+	case 1:
+		gige_pcicfg_write8(dev, reg, val);
+		break;
+	case 2:
+		gige_pcicfg_write16(dev, reg, val);
+		break;
+	case 4:
+		gige_pcicfg_write32(dev, reg, val);
+		break;
+	default:
+		WARN_ON(1);
+	}
+	spin_unlock_irqrestore(&dev->lock, flags);
+
+	return PCIBIOS_SUCCESSFUL;
+}
+
+static int ssb_gige_probe(struct ssb_device *sdev,
+			  const struct ssb_device_id *id)
+{
+	struct ssb_gige *dev;
+	u32 base, tmslow, tmshigh;
+
+	dev = kzalloc_obj(*dev);
+	if (!dev)
+		return -ENOMEM;
+	dev->dev = sdev;
+
+	spin_lock_init(&dev->lock);
+	dev->pci_controller.pci_ops = &dev->pci_ops;
+	dev->pci_controller.io_resource = &dev->io_resource;
+	dev->pci_controller.mem_resource = &dev->mem_resource;
+	dev->pci_controller.io_map_base = 0x800;
+	dev->pci_ops.read = ssb_gige_pci_read_config;
+	dev->pci_ops.write = ssb_gige_pci_write_config;
+
+	dev->io_resource.name = SSB_GIGE_IO_RES_NAME;
+	dev->io_resource.start = 0x800;
+	dev->io_resource.end = 0x8FF;
+	dev->io_resource.flags = IORESOURCE_IO | IORESOURCE_PCI_FIXED;
+
+	if (!ssb_device_is_enabled(sdev))
+		ssb_device_enable(sdev, 0);
+
+	/* Setup BAR0. This is a 64k MMIO region. */
+	base = ssb_admatch_base(ssb_read32(sdev, SSB_ADMATCH1));
+	gige_pcicfg_write32(dev, PCI_BASE_ADDRESS_0, base);
+	gige_pcicfg_write32(dev, PCI_BASE_ADDRESS_1, 0);
+
+	dev->mem_resource.name = SSB_GIGE_MEM_RES_NAME;
+	dev->mem_resource.start = base;
+	dev->mem_resource.end = base + 0x10000 - 1;
+	dev->mem_resource.flags = IORESOURCE_MEM | IORESOURCE_PCI_FIXED;
+
+	/* Enable the memory region. */
+	gige_pcicfg_write16(dev, PCI_COMMAND,
+			    gige_pcicfg_read16(dev, PCI_COMMAND)
+			    | PCI_COMMAND_MEMORY);
+
+	/* Write flushing is controlled by the Flush Status Control register.
+	 * We want to flush every register write with a timeout and we want
+	 * to disable the IRQ mask while flushing to avoid concurrency.
+	 * Note that automatic write flushing does _not_ work from
+	 * an IRQ handler. The driver must flush manually by reading a register.
+	 */
+	gige_write32(dev, SSB_GIGE_SHIM_FLUSHSTAT, 0x00000068);
+
+	/* Check if we have an RGMII or GMII PHY-bus.
+	 * On RGMII do not bypass the DLLs */
+	tmslow = ssb_read32(sdev, SSB_TMSLOW);
+	tmshigh = ssb_read32(sdev, SSB_TMSHIGH);
+	if (tmshigh & SSB_GIGE_TMSHIGH_RGMII) {
+		tmslow &= ~SSB_GIGE_TMSLOW_TXBYPASS;
+		tmslow &= ~SSB_GIGE_TMSLOW_RXBYPASS;
+		dev->has_rgmii = 1;
+	} else {
+		tmslow |= SSB_GIGE_TMSLOW_TXBYPASS;
+		tmslow |= SSB_GIGE_TMSLOW_RXBYPASS;
+		dev->has_rgmii = 0;
+	}
+	tmslow |= SSB_GIGE_TMSLOW_DLLEN;
+	ssb_write32(sdev, SSB_TMSLOW, tmslow);
+
+	ssb_set_drvdata(sdev, dev);
+	register_pci_controller(&dev->pci_controller);
+
+	return 0;
+}
+
+bool pdev_is_ssb_gige_core(struct pci_dev *pdev)
+{
+	if (!pdev->resource[0].name)
+		return false;
+	return (strcmp(pdev->resource[0].name, SSB_GIGE_MEM_RES_NAME) == 0);
+}
+EXPORT_SYMBOL(pdev_is_ssb_gige_core);
+
+int ssb_gige_pcibios_plat_dev_init(struct ssb_device *sdev,
+				   struct pci_dev *pdev)
+{
+	struct ssb_gige *dev = ssb_get_drvdata(sdev);
+	struct resource *res;
+
+	if (pdev->bus->ops != &dev->pci_ops) {
+		/* The PCI device is not on this SSB GigE bridge device. */
+		return -ENODEV;
+	}
+
+	/* Fixup the PCI resources. */
+	res = &(pdev->resource[0]);
+	res->flags = IORESOURCE_MEM | IORESOURCE_PCI_FIXED;
+	res->name = dev->mem_resource.name;
+	res->start = dev->mem_resource.start;
+	res->end = dev->mem_resource.end;
+
+	/* Fixup interrupt lines. */
+	pdev->irq = ssb_mips_irq(sdev) + 2;
+	pci_write_config_byte(pdev, PCI_INTERRUPT_LINE, pdev->irq);
+
+	return 0;
+}
+
+int ssb_gige_map_irq(struct ssb_device *sdev,
+		     const struct pci_dev *pdev)
+{
+	struct ssb_gige *dev = ssb_get_drvdata(sdev);
+
+	if (pdev->bus->ops != &dev->pci_ops) {
+		/* The PCI device is not on this SSB GigE bridge device. */
+		return -ENODEV;
+	}
+
+	return ssb_mips_irq(sdev) + 2;
+}
+
+static struct ssb_driver ssb_gige_driver = {
+	.name		= "BCM-GigE",
+	.id_table	= ssb_gige_tbl,
+	.probe		= ssb_gige_probe,
+};
+
+int ssb_gige_init(void)
+{
+	return ssb_driver_register(&ssb_gige_driver);
+}