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, 159 insertions, 0 deletions

diff --git a/drivers/nvmem/mtk-efuse.c b/drivers/nvmem/mtk-efuse.c
new file mode 100644
index 000000000..00a84ea96
--- /dev/null
+++ b/drivers/nvmem/mtk-efuse.c
@@ -0,0 +1,159 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2015 MediaTek Inc.
+ * Author: Andrew-CT Chen <andrew-ct.chen@mediatek.com>
+ */
+
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/io.h>
+#include <linux/nvmem-provider.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+
+struct mtk_efuse_pdata {
+	bool uses_post_processing;
+};
+
+struct mtk_efuse_priv {
+	void __iomem *base;
+};
+
+static int mtk_reg_read(void *context,
+			unsigned int reg, void *_val, size_t bytes)
+{
+	struct mtk_efuse_priv *priv = context;
+	void __iomem *addr = priv->base + reg;
+	u8 *val = _val;
+	int i;
+
+	for (i = 0; i < bytes; i++, val++)
+		*val = readb(addr + i);
+
+	return 0;
+}
+
+static int mtk_efuse_gpu_speedbin_pp(void *context, const char *id, int index,
+				     unsigned int offset, void *data, size_t bytes)
+{
+	u8 *val = data;
+
+	if (val[0] < 8)
+		val[0] = BIT(val[0]);
+
+	return 0;
+}
+
+static void mtk_efuse_fixup_dt_cell_info(struct nvmem_device *nvmem,
+					 struct nvmem_cell_info *cell)
+{
+	size_t sz = strlen(cell->name);
+
+	/*
+	 * On some SoCs, the GPU speedbin is not read as bitmask but as
+	 * a number with range [0-7] (max 3 bits): post process to use
+	 * it in OPP tables to describe supported-hw.
+	 */
+	if (cell->nbits <= 3 &&
+	    strncmp(cell->name, "gpu-speedbin", min(sz, strlen("gpu-speedbin"))) == 0)
+		cell->read_post_process = mtk_efuse_gpu_speedbin_pp;
+}
+
+static int mtk_efuse_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct resource *res;
+	struct nvmem_device *nvmem;
+	struct nvmem_config econfig = {};
+	struct mtk_efuse_priv *priv;
+	const struct mtk_efuse_pdata *pdata;
+	struct platform_device *socinfo;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
+	if (IS_ERR(priv->base))
+		return PTR_ERR(priv->base);
+
+	pdata = device_get_match_data(dev);
+	econfig.add_legacy_fixed_of_cells = true;
+	econfig.stride = 1;
+	econfig.word_size = 1;
+	econfig.reg_read = mtk_reg_read;
+	econfig.size = resource_size(res);
+	econfig.priv = priv;
+	econfig.dev = dev;
+	if (pdata->uses_post_processing)
+		econfig.fixup_dt_cell_info = &mtk_efuse_fixup_dt_cell_info;
+	nvmem = devm_nvmem_register(dev, &econfig);
+	if (IS_ERR(nvmem))
+		return PTR_ERR(nvmem);
+
+	socinfo = platform_device_register_data(&pdev->dev, "mtk-socinfo",
+						PLATFORM_DEVID_AUTO, NULL, 0);
+	if (IS_ERR(socinfo))
+		dev_info(dev, "MediaTek SoC Information will be unavailable\n");
+
+	platform_set_drvdata(pdev, socinfo);
+	return 0;
+}
+
+static const struct mtk_efuse_pdata mtk_mt8186_efuse_pdata = {
+	.uses_post_processing = true,
+};
+
+static const struct mtk_efuse_pdata mtk_efuse_pdata = {
+	.uses_post_processing = false,
+};
+
+static const struct of_device_id mtk_efuse_of_match[] = {
+	{ .compatible = "mediatek,mt8173-efuse", .data = &mtk_efuse_pdata },
+	{ .compatible = "mediatek,mt8186-efuse", .data = &mtk_mt8186_efuse_pdata },
+	{ .compatible = "mediatek,efuse", .data = &mtk_efuse_pdata },
+	{/* sentinel */},
+};
+MODULE_DEVICE_TABLE(of, mtk_efuse_of_match);
+
+static void mtk_efuse_remove(struct platform_device *pdev)
+{
+	struct platform_device *socinfo = platform_get_drvdata(pdev);
+
+	if (!IS_ERR_OR_NULL(socinfo))
+		platform_device_unregister(socinfo);
+}
+
+static struct platform_driver mtk_efuse_driver = {
+	.probe = mtk_efuse_probe,
+	.remove = mtk_efuse_remove,
+	.driver = {
+		.name = "mediatek,efuse",
+		.of_match_table = mtk_efuse_of_match,
+	},
+};
+
+static int __init mtk_efuse_init(void)
+{
+	int ret;
+
+	ret = platform_driver_register(&mtk_efuse_driver);
+	if (ret) {
+		pr_err("Failed to register efuse driver\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static void __exit mtk_efuse_exit(void)
+{
+	return platform_driver_unregister(&mtk_efuse_driver);
+}
+
+subsys_initcall(mtk_efuse_init);
+module_exit(mtk_efuse_exit);
+
+MODULE_AUTHOR("Andrew-CT Chen <andrew-ct.chen@mediatek.com>");
+MODULE_DESCRIPTION("Mediatek EFUSE driver");
+MODULE_LICENSE("GPL v2");