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, 116 insertions, 0 deletions

diff --git a/drivers/bus/tegra-aconnect.c b/drivers/bus/tegra-aconnect.c
new file mode 100644
index 000000000..9b2b22733
--- /dev/null
+++ b/drivers/bus/tegra-aconnect.c
@@ -0,0 +1,116 @@
+/*
+ * Tegra ACONNECT Bus Driver
+ *
+ * Copyright (C) 2016, NVIDIA CORPORATION.  All rights reserved.
+ *
+ * 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/clk.h>
+#include <linux/module.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/pm_runtime.h>
+
+struct tegra_aconnect {
+	struct clk	*ape_clk;
+	struct clk	*apb2ape_clk;
+};
+
+static int tegra_aconnect_probe(struct platform_device *pdev)
+{
+	struct tegra_aconnect *aconnect;
+
+	if (!pdev->dev.of_node)
+		return -EINVAL;
+
+	aconnect = devm_kzalloc(&pdev->dev, sizeof(struct tegra_aconnect),
+				GFP_KERNEL);
+	if (!aconnect)
+		return -ENOMEM;
+
+	aconnect->ape_clk = devm_clk_get(&pdev->dev, "ape");
+	if (IS_ERR(aconnect->ape_clk))
+		return dev_err_probe(&pdev->dev, PTR_ERR(aconnect->ape_clk),
+				     "can't retrieve ape clock\n");
+
+	aconnect->apb2ape_clk = devm_clk_get(&pdev->dev, "apb2ape");
+	if (IS_ERR(aconnect->apb2ape_clk))
+		return dev_err_probe(&pdev->dev, PTR_ERR(aconnect->apb2ape_clk),
+				     "can't retrieve apb2ape clock\n");
+
+	dev_set_drvdata(&pdev->dev, aconnect);
+	pm_runtime_enable(&pdev->dev);
+
+	of_platform_populate(pdev->dev.of_node, NULL, NULL, &pdev->dev);
+
+	dev_info(&pdev->dev, "Tegra ACONNECT bus registered\n");
+
+	return 0;
+}
+
+static void tegra_aconnect_remove(struct platform_device *pdev)
+{
+	pm_runtime_disable(&pdev->dev);
+}
+
+static int tegra_aconnect_runtime_resume(struct device *dev)
+{
+	struct tegra_aconnect *aconnect = dev_get_drvdata(dev);
+	int ret;
+
+	ret = clk_prepare_enable(aconnect->ape_clk);
+	if (ret) {
+		dev_err(dev, "ape clk_enable failed: %d\n", ret);
+		return ret;
+	}
+
+	ret = clk_prepare_enable(aconnect->apb2ape_clk);
+	if (ret) {
+		clk_disable_unprepare(aconnect->ape_clk);
+		dev_err(dev, "apb2ape clk_enable failed: %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+static int tegra_aconnect_runtime_suspend(struct device *dev)
+{
+	struct tegra_aconnect *aconnect = dev_get_drvdata(dev);
+
+	clk_disable_unprepare(aconnect->ape_clk);
+	clk_disable_unprepare(aconnect->apb2ape_clk);
+
+	return 0;
+}
+
+static const struct dev_pm_ops tegra_aconnect_pm_ops = {
+	SET_RUNTIME_PM_OPS(tegra_aconnect_runtime_suspend,
+			   tegra_aconnect_runtime_resume, NULL)
+	SET_NOIRQ_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend,
+				      pm_runtime_force_resume)
+};
+
+static const struct of_device_id tegra_aconnect_of_match[] = {
+	{ .compatible = "nvidia,tegra210-aconnect", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, tegra_aconnect_of_match);
+
+static struct platform_driver tegra_aconnect_driver = {
+	.probe = tegra_aconnect_probe,
+	.remove = tegra_aconnect_remove,
+	.driver = {
+		.name = "tegra-aconnect",
+		.of_match_table = tegra_aconnect_of_match,
+		.pm = &tegra_aconnect_pm_ops,
+	},
+};
+module_platform_driver(tegra_aconnect_driver);
+
+MODULE_DESCRIPTION("NVIDIA Tegra ACONNECT Bus Driver");
+MODULE_AUTHOR("Jon Hunter <jonathanh@nvidia.com>");
+MODULE_LICENSE("GPL v2");