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, 208 insertions, 0 deletions

diff --git a/drivers/tc/tc.c b/drivers/tc/tc.c
new file mode 100644
index 000000000..ebc835cf1
--- /dev/null
+++ b/drivers/tc/tc.c
@@ -0,0 +1,208 @@
+/*
+ *	TURBOchannel bus services.
+ *
+ *	Copyright (c) Harald Koerfgen, 1998
+ *	Copyright (c) 2001, 2003, 2005, 2006, 2018  Maciej W. Rozycki
+ *	Copyright (c) 2005  James Simmons
+ *
+ *	This file is subject to the terms and conditions of the GNU
+ *	General Public License.  See the file "COPYING" in the main
+ *	directory of this archive for more details.
+ */
+#include <linux/compiler.h>
+#include <linux/dma-mapping.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/ioport.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/tc.h>
+#include <linux/types.h>
+
+#include <asm/io.h>
+
+static struct tc_bus tc_bus = {
+	.name = "TURBOchannel",
+};
+
+/*
+ * Probing for TURBOchannel modules.
+ */
+static void __init tc_bus_add_devices(struct tc_bus *tbus)
+{
+	resource_size_t slotsize = tbus->info.slot_size << 20;
+	resource_size_t extslotsize = tbus->ext_slot_size;
+	resource_size_t slotaddr;
+	resource_size_t extslotaddr;
+	resource_size_t devsize;
+	void __iomem *module;
+	struct tc_dev *tdev;
+	int i, slot, err;
+	u8 pattern[4];
+	long offset;
+
+	for (slot = 0; slot < tbus->num_tcslots; slot++) {
+		slotaddr = tbus->slot_base + slot * slotsize;
+		extslotaddr = tbus->ext_slot_base + slot * extslotsize;
+		module = ioremap(slotaddr, slotsize);
+		BUG_ON(!module);
+
+		offset = TC_OLDCARD;
+
+		err = 0;
+		err |= tc_preadb(pattern + 0, module + offset + TC_PATTERN0);
+		err |= tc_preadb(pattern + 1, module + offset + TC_PATTERN1);
+		err |= tc_preadb(pattern + 2, module + offset + TC_PATTERN2);
+		err |= tc_preadb(pattern + 3, module + offset + TC_PATTERN3);
+		if (err)
+			goto out_err;
+
+		if (pattern[0] != 0x55 || pattern[1] != 0x00 ||
+		    pattern[2] != 0xaa || pattern[3] != 0xff) {
+			offset = TC_NEWCARD;
+
+			err = 0;
+			err |= tc_preadb(pattern + 0,
+					 module + offset + TC_PATTERN0);
+			err |= tc_preadb(pattern + 1,
+					 module + offset + TC_PATTERN1);
+			err |= tc_preadb(pattern + 2,
+					 module + offset + TC_PATTERN2);
+			err |= tc_preadb(pattern + 3,
+					 module + offset + TC_PATTERN3);
+			if (err)
+				goto out_err;
+		}
+
+		if (pattern[0] != 0x55 || pattern[1] != 0x00 ||
+		    pattern[2] != 0xaa || pattern[3] != 0xff)
+			goto out_err;
+
+		/* Found a board, allocate it an entry in the list */
+		tdev = kzalloc_obj(*tdev);
+		if (!tdev) {
+			pr_err("tc%x: unable to allocate tc_dev\n", slot);
+			goto out_err;
+		}
+		dev_set_name(&tdev->dev, "tc%x", slot);
+		tdev->bus = tbus;
+		tdev->dev.parent = &tbus->dev;
+		tdev->dev.bus = &tc_bus_type;
+		tdev->slot = slot;
+
+		/* TURBOchannel has 34-bit DMA addressing (16GiB space). */
+		tdev->dma_mask = DMA_BIT_MASK(34);
+		tdev->dev.dma_mask = &tdev->dma_mask;
+		tdev->dev.coherent_dma_mask = DMA_BIT_MASK(34);
+
+		for (i = 0; i < 8; i++) {
+			tdev->firmware[i] =
+				readb(module + offset + TC_FIRM_VER + 4 * i);
+			tdev->vendor[i] =
+				readb(module + offset + TC_VENDOR + 4 * i);
+			tdev->name[i] =
+				readb(module + offset + TC_MODULE + 4 * i);
+		}
+		tdev->firmware[8] = 0;
+		tdev->vendor[8] = 0;
+		tdev->name[8] = 0;
+
+		pr_info("%s: %s %s %s\n", dev_name(&tdev->dev), tdev->vendor,
+			tdev->name, tdev->firmware);
+
+		devsize = readb(module + offset + TC_SLOT_SIZE);
+		devsize <<= 22;
+		if (devsize <= slotsize) {
+			tdev->resource.start = slotaddr;
+			tdev->resource.end = slotaddr + devsize - 1;
+		} else if (devsize <= extslotsize) {
+			tdev->resource.start = extslotaddr;
+			tdev->resource.end = extslotaddr + devsize - 1;
+		} else {
+			pr_err("%s: Cannot provide slot space "
+			       "(%ldMiB required, up to %ldMiB supported)\n",
+			       dev_name(&tdev->dev), (long)(devsize >> 20),
+			       (long)(max(slotsize, extslotsize) >> 20));
+			kfree(tdev);
+			goto out_err;
+		}
+		tdev->resource.name = tdev->name;
+		tdev->resource.flags = IORESOURCE_MEM;
+
+		tc_device_get_irq(tdev);
+
+		if (device_register(&tdev->dev)) {
+			put_device(&tdev->dev);
+			goto out_err;
+		}
+		list_add_tail(&tdev->node, &tbus->devices);
+
+out_err:
+		iounmap(module);
+	}
+}
+
+/*
+ * The main entry.
+ */
+static int __init tc_init(void)
+{
+	/* Initialize the TURBOchannel bus */
+	if (tc_bus_get_info(&tc_bus))
+		goto out_err;
+
+	INIT_LIST_HEAD(&tc_bus.devices);
+	dev_set_name(&tc_bus.dev, "tc");
+	if (device_register(&tc_bus.dev))
+		goto out_err_device;
+
+	if (tc_bus.info.slot_size) {
+		unsigned int tc_clock = tc_get_speed(&tc_bus) / 100000;
+
+		pr_info("tc: TURBOchannel rev. %d at %u.%u MHz "
+			"(with%s parity)\n", tc_bus.info.revision,
+			tc_clock / 10, tc_clock % 10,
+			tc_bus.info.parity ? "" : "out");
+
+		tc_bus.resource[0].start = tc_bus.slot_base;
+		tc_bus.resource[0].end = tc_bus.slot_base +
+					 (tc_bus.info.slot_size << 20) *
+					 tc_bus.num_tcslots - 1;
+		tc_bus.resource[0].name = tc_bus.name;
+		tc_bus.resource[0].flags = IORESOURCE_MEM;
+		if (request_resource(&iomem_resource,
+				     &tc_bus.resource[0]) < 0) {
+			pr_err("tc: Cannot reserve resource\n");
+			goto out_err_device;
+		}
+		if (tc_bus.ext_slot_size) {
+			tc_bus.resource[1].start = tc_bus.ext_slot_base;
+			tc_bus.resource[1].end = tc_bus.ext_slot_base +
+						 tc_bus.ext_slot_size *
+						 tc_bus.num_tcslots - 1;
+			tc_bus.resource[1].name = tc_bus.name;
+			tc_bus.resource[1].flags = IORESOURCE_MEM;
+			if (request_resource(&iomem_resource,
+					     &tc_bus.resource[1]) < 0) {
+				pr_err("tc: Cannot reserve resource\n");
+				goto out_err_resource;
+			}
+		}
+
+		tc_bus_add_devices(&tc_bus);
+	}
+
+	return 0;
+
+out_err_resource:
+	release_resource(&tc_bus.resource[0]);
+out_err_device:
+	put_device(&tc_bus.dev);
+out_err:
+	return 0;
+}
+
+subsys_initcall(tc_init);