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, 324 insertions, 0 deletions

diff --git a/drivers/mtd/maps/pci.c b/drivers/mtd/maps/pci.c
new file mode 100644
index 000000000..34041cc8f
--- /dev/null
+++ b/drivers/mtd/maps/pci.c
@@ -0,0 +1,324 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  linux/drivers/mtd/maps/pci.c
+ *
+ *  Copyright (C) 2001 Russell King, All rights reserved.
+ *
+ * Generic PCI memory map driver.  We support the following boards:
+ *  - Intel IQ80310 ATU.
+ *  - Intel EBSA285 (blank rom programming mode). Tested working 27/09/2001
+ */
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/pci.h>
+#include <linux/slab.h>
+
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/map.h>
+#include <linux/mtd/partitions.h>
+
+struct map_pci_info;
+
+struct mtd_pci_info {
+	int  (*init)(struct pci_dev *dev, struct map_pci_info *map);
+	void (*exit)(struct pci_dev *dev, struct map_pci_info *map);
+	unsigned long (*translate)(struct map_pci_info *map, unsigned long ofs);
+	const char *map_name;
+};
+
+struct map_pci_info {
+	struct map_info map;
+	void __iomem *base;
+	void (*exit)(struct pci_dev *dev, struct map_pci_info *map);
+	unsigned long (*translate)(struct map_pci_info *map, unsigned long ofs);
+	struct pci_dev *dev;
+};
+
+static map_word mtd_pci_read8(struct map_info *_map, unsigned long ofs)
+{
+	struct map_pci_info *map = (struct map_pci_info *)_map;
+	map_word val;
+	val.x[0]= readb(map->base + map->translate(map, ofs));
+	return val;
+}
+
+static map_word mtd_pci_read32(struct map_info *_map, unsigned long ofs)
+{
+	struct map_pci_info *map = (struct map_pci_info *)_map;
+	map_word val;
+	val.x[0] = readl(map->base + map->translate(map, ofs));
+	return val;
+}
+
+static void mtd_pci_copyfrom(struct map_info *_map, void *to, unsigned long from, ssize_t len)
+{
+	struct map_pci_info *map = (struct map_pci_info *)_map;
+	memcpy_fromio(to, map->base + map->translate(map, from), len);
+}
+
+static void mtd_pci_write8(struct map_info *_map, map_word val, unsigned long ofs)
+{
+	struct map_pci_info *map = (struct map_pci_info *)_map;
+	writeb(val.x[0], map->base + map->translate(map, ofs));
+}
+
+static void mtd_pci_write32(struct map_info *_map, map_word val, unsigned long ofs)
+{
+	struct map_pci_info *map = (struct map_pci_info *)_map;
+	writel(val.x[0], map->base + map->translate(map, ofs));
+}
+
+static void mtd_pci_copyto(struct map_info *_map, unsigned long to, const void *from, ssize_t len)
+{
+	struct map_pci_info *map = (struct map_pci_info *)_map;
+	memcpy_toio(map->base + map->translate(map, to), from, len);
+}
+
+static const struct map_info mtd_pci_map = {
+	.phys =		NO_XIP,
+	.copy_from =	mtd_pci_copyfrom,
+	.copy_to =	mtd_pci_copyto,
+};
+
+/*
+ * Intel IOP80310 Flash driver
+ */
+
+static int
+intel_iq80310_init(struct pci_dev *dev, struct map_pci_info *map)
+{
+	u32 win_base;
+
+	map->map.bankwidth = 1;
+	map->map.read = mtd_pci_read8;
+	map->map.write = mtd_pci_write8;
+
+	map->map.size     = 0x00800000;
+	map->base         = ioremap(pci_resource_start(dev, 0),
+					    pci_resource_len(dev, 0));
+
+	if (!map->base)
+		return -ENOMEM;
+
+	/*
+	 * We want to base the memory window at Xscale
+	 * bus address 0, not 0x1000.
+	 */
+	pci_read_config_dword(dev, 0x44, &win_base);
+	pci_write_config_dword(dev, 0x44, 0);
+
+	map->map.map_priv_2 = win_base;
+
+	return 0;
+}
+
+static void
+intel_iq80310_exit(struct pci_dev *dev, struct map_pci_info *map)
+{
+	if (map->base)
+		iounmap(map->base);
+	pci_write_config_dword(dev, 0x44, map->map.map_priv_2);
+}
+
+static unsigned long
+intel_iq80310_translate(struct map_pci_info *map, unsigned long ofs)
+{
+	unsigned long page_addr = ofs & 0x00400000;
+
+	/*
+	 * This mundges the flash location so we avoid
+	 * the first 80 bytes (they appear to read nonsense).
+	 */
+	if (page_addr) {
+		writel(0x00000008, map->base + 0x1558);
+		writel(0x00000000, map->base + 0x1550);
+	} else {
+		writel(0x00000007, map->base + 0x1558);
+		writel(0x00800000, map->base + 0x1550);
+		ofs += 0x00800000;
+	}
+
+	return ofs;
+}
+
+static struct mtd_pci_info intel_iq80310_info = {
+	.init =		intel_iq80310_init,
+	.exit =		intel_iq80310_exit,
+	.translate =	intel_iq80310_translate,
+	.map_name =	"cfi_probe",
+};
+
+/*
+ * Intel DC21285 driver
+ */
+
+static int
+intel_dc21285_init(struct pci_dev *dev, struct map_pci_info *map)
+{
+	unsigned long base, len;
+
+	base = pci_resource_start(dev, PCI_ROM_RESOURCE);
+	len  = pci_resource_len(dev, PCI_ROM_RESOURCE);
+
+	if (!len || !base) {
+		/*
+		 * No ROM resource
+		 */
+		base = pci_resource_start(dev, 2);
+		len  = pci_resource_len(dev, 2);
+
+		/*
+		 * We need to re-allocate PCI BAR2 address range to the
+		 * PCI ROM BAR, and disable PCI BAR2.
+		 */
+	} else {
+		/*
+		 * Hmm, if an address was allocated to the ROM resource, but
+		 * not enabled, should we be allocating a new resource for it
+		 * or simply enabling it?
+		 */
+		pci_enable_rom(dev);
+		printk("%s: enabling expansion ROM\n", pci_name(dev));
+	}
+
+	if (!len || !base)
+		return -ENXIO;
+
+	map->map.bankwidth = 4;
+	map->map.read = mtd_pci_read32;
+	map->map.write = mtd_pci_write32;
+	map->map.size     = len;
+	map->base         = ioremap(base, len);
+
+	if (!map->base)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static void
+intel_dc21285_exit(struct pci_dev *dev, struct map_pci_info *map)
+{
+	if (map->base)
+		iounmap(map->base);
+
+	/*
+	 * We need to undo the PCI BAR2/PCI ROM BAR address alteration.
+	 */
+	pci_disable_rom(dev);
+}
+
+static unsigned long
+intel_dc21285_translate(struct map_pci_info *map, unsigned long ofs)
+{
+	return ofs & 0x00ffffc0 ? ofs : (ofs ^ (1 << 5));
+}
+
+static struct mtd_pci_info intel_dc21285_info = {
+	.init =		intel_dc21285_init,
+	.exit =		intel_dc21285_exit,
+	.translate =	intel_dc21285_translate,
+	.map_name =	"jedec_probe",
+};
+
+/*
+ * PCI device ID table
+ */
+
+static const struct pci_device_id mtd_pci_ids[] = {
+	{
+		PCI_DEVICE(PCI_VENDOR_ID_INTEL, 0x530d),
+		.class =	PCI_CLASS_MEMORY_OTHER << 8,
+		.class_mask =	0xffff00,
+		.driver_data =	(unsigned long)&intel_iq80310_info,
+	}, {
+		/* DC21285 defaults to 0 for .subvendor and .subdevice on reset */
+		PCI_DEVICE_SUB(PCI_VENDOR_ID_DEC, PCI_DEVICE_ID_DEC_21285, 0, 0),
+		.driver_data =	(unsigned long)&intel_dc21285_info,
+	},
+	{ }
+};
+
+/*
+ * Generic code follows.
+ */
+
+static int mtd_pci_probe(struct pci_dev *dev, const struct pci_device_id *id)
+{
+	struct mtd_pci_info *info = (struct mtd_pci_info *)id->driver_data;
+	struct map_pci_info *map = NULL;
+	struct mtd_info *mtd = NULL;
+	int err;
+
+	err = pci_enable_device(dev);
+	if (err)
+		goto out;
+
+	err = pci_request_regions(dev, "pci mtd");
+	if (err)
+		goto out;
+
+	map = kmalloc_obj(*map);
+	err = -ENOMEM;
+	if (!map)
+		goto release;
+
+	map->map       = mtd_pci_map;
+	map->map.name  = pci_name(dev);
+	map->dev       = dev;
+	map->exit      = info->exit;
+	map->translate = info->translate;
+
+	err = info->init(dev, map);
+	if (err)
+		goto release;
+
+	mtd = do_map_probe(info->map_name, &map->map);
+	err = -ENODEV;
+	if (!mtd)
+		goto release;
+
+	mtd->owner = THIS_MODULE;
+	mtd_device_register(mtd, NULL, 0);
+
+	pci_set_drvdata(dev, mtd);
+
+	return 0;
+
+release:
+	if (map) {
+		map->exit(dev, map);
+		kfree(map);
+	}
+
+	pci_release_regions(dev);
+out:
+	return err;
+}
+
+static void mtd_pci_remove(struct pci_dev *dev)
+{
+	struct mtd_info *mtd = pci_get_drvdata(dev);
+	struct map_pci_info *map = mtd->priv;
+
+	mtd_device_unregister(mtd);
+	map_destroy(mtd);
+	map->exit(dev, map);
+	kfree(map);
+
+	pci_release_regions(dev);
+}
+
+static struct pci_driver mtd_pci_driver = {
+	.name =		"MTD PCI",
+	.probe =	mtd_pci_probe,
+	.remove =	mtd_pci_remove,
+	.id_table =	mtd_pci_ids,
+};
+
+module_pci_driver(mtd_pci_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Russell King <rmk@arm.linux.org.uk>");
+MODULE_DESCRIPTION("Generic PCI map driver");
+MODULE_DEVICE_TABLE(pci, mtd_pci_ids);