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, 79 insertions, 0 deletions

diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h
new file mode 100644
index 000000000..5909171a4
--- /dev/null
+++ b/drivers/dax/bus.h
@@ -0,0 +1,79 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright(c) 2016 - 2018 Intel Corporation. All rights reserved. */
+#ifndef __DAX_BUS_H__
+#define __DAX_BUS_H__
+#include <linux/device.h>
+#include <linux/platform_device.h>
+#include <linux/range.h>
+#include <linux/workqueue.h>
+
+struct dev_dax;
+struct resource;
+struct dax_device;
+struct dax_region;
+
+/* dax bus specific ioresource flags */
+#define IORESOURCE_DAX_STATIC BIT(0)
+#define IORESOURCE_DAX_KMEM BIT(1)
+
+struct dax_region *alloc_dax_region(struct device *parent, int region_id,
+		struct range *range, int target_node, unsigned int align,
+		unsigned long flags);
+
+struct dev_dax_data {
+	struct dax_region *dax_region;
+	struct dev_pagemap *pgmap;
+	resource_size_t size;
+	int id;
+	bool memmap_on_memory;
+};
+
+struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data);
+
+enum dax_driver_type {
+	DAXDRV_KMEM_TYPE,
+	DAXDRV_DEVICE_TYPE,
+	DAXDRV_FSDEV_TYPE,
+};
+
+struct dax_device_driver {
+	struct device_driver drv;
+	struct list_head ids;
+	enum dax_driver_type type;
+	int (*probe)(struct dev_dax *dev);
+	void (*remove)(struct dev_dax *dev);
+};
+
+#define to_dax_drv(__drv) container_of_const(__drv, struct dax_device_driver, drv)
+
+int __dax_driver_register(struct dax_device_driver *dax_drv,
+		struct module *module, const char *mod_name);
+#define dax_driver_register(driver) \
+	__dax_driver_register(driver, THIS_MODULE, KBUILD_MODNAME)
+void dax_driver_unregister(struct dax_device_driver *dax_drv);
+void kill_dev_dax(struct dev_dax *dev_dax);
+bool static_dev_dax(struct dev_dax *dev_dax);
+
+struct hmem_platform_device {
+	struct platform_device pdev;
+	struct work_struct work;
+	bool did_probe;
+};
+
+static inline struct hmem_platform_device *
+to_hmem_platform_device(struct platform_device *pdev)
+{
+	return container_of(pdev, struct hmem_platform_device, pdev);
+}
+
+#if IS_ENABLED(CONFIG_DEV_DAX_HMEM)
+void dax_hmem_flush_work(void);
+#else
+static inline void dax_hmem_flush_work(void) { }
+#endif
+
+#define MODULE_ALIAS_DAX_DEVICE(type) \
+	MODULE_ALIAS("dax:t" __stringify(type) "*")
+#define DAX_DEVICE_MODALIAS_FMT "dax:t%d"
+
+#endif /* __DAX_BUS_H__ */