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, 188 insertions, 0 deletions

diff --git a/drivers/mfd/lpc_sch.c b/drivers/mfd/lpc_sch.c
new file mode 100644
index 000000000..d069165f9
--- /dev/null
+++ b/drivers/mfd/lpc_sch.c
@@ -0,0 +1,188 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  lpc_sch.c - LPC interface for Intel Poulsbo SCH
+ *
+ *  LPC bridge function of the Intel SCH contains many other
+ *  functional units, such as Interrupt controllers, Timers,
+ *  Power Management, System Management, GPIO, RTC, and LPC
+ *  Configuration Registers.
+ *
+ *  Copyright (c) 2010 CompuLab Ltd
+ *  Copyright (c) 2014 Intel Corp.
+ *  Author: Denis Turischev <denis@compulab.co.il>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/acpi.h>
+#include <linux/pci.h>
+#include <linux/mfd/core.h>
+
+#define SMBASE		0x40
+#define SMBUS_IO_SIZE	64
+
+#define GPIO_BASE	0x44
+#define GPIO_IO_SIZE	64
+#define GPIO_IO_SIZE_CENTERTON	128
+
+#define WDTBASE		0x84
+#define WDT_IO_SIZE	64
+
+enum sch_chipsets {
+	LPC_SCH = 0,		/* Intel Poulsbo SCH */
+	LPC_ITC,		/* Intel Tunnel Creek */
+	LPC_CENTERTON,		/* Intel Centerton */
+	LPC_QUARK_X1000,	/* Intel Quark X1000 */
+};
+
+struct lpc_sch_info {
+	unsigned int io_size_smbus;
+	unsigned int io_size_gpio;
+	unsigned int io_size_wdt;
+};
+
+static struct lpc_sch_info sch_chipset_info[] = {
+	[LPC_SCH] = {
+		.io_size_smbus = SMBUS_IO_SIZE,
+		.io_size_gpio = GPIO_IO_SIZE,
+	},
+	[LPC_ITC] = {
+		.io_size_smbus = SMBUS_IO_SIZE,
+		.io_size_gpio = GPIO_IO_SIZE,
+		.io_size_wdt = WDT_IO_SIZE,
+	},
+	[LPC_CENTERTON] = {
+		.io_size_smbus = SMBUS_IO_SIZE,
+		.io_size_gpio = GPIO_IO_SIZE_CENTERTON,
+		.io_size_wdt = WDT_IO_SIZE,
+	},
+	[LPC_QUARK_X1000] = {
+		.io_size_gpio = GPIO_IO_SIZE,
+		.io_size_wdt = WDT_IO_SIZE,
+	},
+};
+
+static const struct pci_device_id lpc_sch_ids[] = {
+	{ PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_SCH_LPC), .driver_data = LPC_SCH },
+	{ PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_ITC_LPC), .driver_data = LPC_ITC },
+	{ PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_CENTERTON_ILB), .driver_data = LPC_CENTERTON },
+	{ PCI_VDEVICE(INTEL, PCI_DEVICE_ID_INTEL_QUARK_X1000_ILB), .driver_data = LPC_QUARK_X1000 },
+	{ }
+};
+MODULE_DEVICE_TABLE(pci, lpc_sch_ids);
+
+#define LPC_NO_RESOURCE		1
+#define LPC_SKIP_RESOURCE	2
+
+static int lpc_sch_get_io(struct pci_dev *pdev, int where, const char *name,
+			  struct resource *res, int size)
+{
+	unsigned int base_addr_cfg;
+	unsigned short base_addr;
+
+	if (size == 0)
+		return LPC_NO_RESOURCE;
+
+	pci_read_config_dword(pdev, where, &base_addr_cfg);
+	base_addr = 0;
+	if (!(base_addr_cfg & (1 << 31)))
+		dev_warn(&pdev->dev, "Decode of the %s I/O range disabled\n",
+			 name);
+	else
+		base_addr = (unsigned short)base_addr_cfg;
+
+	if (base_addr == 0) {
+		dev_warn(&pdev->dev, "I/O space for %s uninitialized\n", name);
+		return LPC_SKIP_RESOURCE;
+	}
+
+	res->start = base_addr;
+	res->end = base_addr + size - 1;
+	res->flags = IORESOURCE_IO;
+
+	return 0;
+}
+
+static int lpc_sch_populate_cell(struct pci_dev *pdev, int where,
+				 const char *name, int size, int id,
+				 struct mfd_cell *cell)
+{
+	struct resource *res;
+	int ret;
+
+	res = devm_kzalloc(&pdev->dev, sizeof(*res), GFP_KERNEL);
+	if (!res)
+		return -ENOMEM;
+
+	ret = lpc_sch_get_io(pdev, where, name, res, size);
+	if (ret)
+		return ret;
+
+	memset(cell, 0, sizeof(*cell));
+
+	cell->name = name;
+	cell->resources = res;
+	cell->num_resources = 1;
+	cell->ignore_resource_conflicts = true;
+	cell->id = id;
+
+	return 0;
+}
+
+static int lpc_sch_probe(struct pci_dev *dev, const struct pci_device_id *id)
+{
+	struct mfd_cell lpc_sch_cells[3];
+	struct lpc_sch_info *info = &sch_chipset_info[id->driver_data];
+	unsigned int cells = 0;
+	int ret;
+
+	ret = lpc_sch_populate_cell(dev, SMBASE, "isch_smbus",
+				    info->io_size_smbus,
+				    id->device, &lpc_sch_cells[cells]);
+	if (ret < 0)
+		return ret;
+	if (ret == 0)
+		cells++;
+
+	ret = lpc_sch_populate_cell(dev, GPIO_BASE, "sch_gpio",
+				    info->io_size_gpio,
+				    id->device, &lpc_sch_cells[cells]);
+	if (ret < 0)
+		return ret;
+	if (ret == 0)
+		cells++;
+
+	ret = lpc_sch_populate_cell(dev, WDTBASE, "ie6xx_wdt",
+				    info->io_size_wdt,
+				    id->device, &lpc_sch_cells[cells]);
+	if (ret < 0)
+		return ret;
+	if (ret == 0)
+		cells++;
+
+	if (cells == 0) {
+		dev_err(&dev->dev, "All decode registers disabled.\n");
+		return -ENODEV;
+	}
+
+	return mfd_add_devices(&dev->dev, 0, lpc_sch_cells, cells, NULL, 0, NULL);
+}
+
+static void lpc_sch_remove(struct pci_dev *dev)
+{
+	mfd_remove_devices(&dev->dev);
+}
+
+static struct pci_driver lpc_sch_driver = {
+	.name		= "lpc_sch",
+	.id_table	= lpc_sch_ids,
+	.probe		= lpc_sch_probe,
+	.remove		= lpc_sch_remove,
+};
+
+module_pci_driver(lpc_sch_driver);
+
+MODULE_AUTHOR("Denis Turischev <denis@compulab.co.il>");
+MODULE_DESCRIPTION("LPC interface for Intel Poulsbo SCH");
+MODULE_LICENSE("GPL");