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, 134 insertions, 0 deletions

diff --git a/drivers/memory/pl353-smc.c b/drivers/memory/pl353-smc.c
new file mode 100644
index 000000000..28a8cc560
--- /dev/null
+++ b/drivers/memory/pl353-smc.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ARM PL353 SMC driver
+ *
+ * Copyright (C) 2012 - 2018 Xilinx, Inc
+ * Author: Punnaiah Choudary Kalluri <punnaiah@xilinx.com>
+ * Author: Naga Sureshkumar Relli <nagasure@xilinx.com>
+ */
+
+#include <linux/clk.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/amba/bus.h>
+
+/**
+ * struct pl353_smc_data - Private smc driver structure
+ * @memclk:		Pointer to the peripheral clock
+ * @aclk:		Pointer to the AXI peripheral clock
+ */
+struct pl353_smc_data {
+	struct clk		*memclk;
+	struct clk		*aclk;
+};
+
+static int __maybe_unused pl353_smc_suspend(struct device *dev)
+{
+	struct pl353_smc_data *pl353_smc = dev_get_drvdata(dev);
+
+	clk_disable(pl353_smc->memclk);
+	clk_disable(pl353_smc->aclk);
+
+	return 0;
+}
+
+static int __maybe_unused pl353_smc_resume(struct device *dev)
+{
+	struct pl353_smc_data *pl353_smc = dev_get_drvdata(dev);
+	int ret;
+
+	ret = clk_enable(pl353_smc->aclk);
+	if (ret) {
+		dev_err(dev, "Cannot enable axi domain clock.\n");
+		return ret;
+	}
+
+	ret = clk_enable(pl353_smc->memclk);
+	if (ret) {
+		dev_err(dev, "Cannot enable memory clock.\n");
+		clk_disable(pl353_smc->aclk);
+		return ret;
+	}
+
+	return ret;
+}
+
+static SIMPLE_DEV_PM_OPS(pl353_smc_dev_pm_ops, pl353_smc_suspend,
+			 pl353_smc_resume);
+
+static const struct of_device_id pl353_smc_supported_children[] = {
+	{
+		.compatible = "cfi-flash"
+	},
+	{
+		.compatible = "arm,pl353-nand-r2p1",
+	},
+	{}
+};
+
+static int pl353_smc_probe(struct amba_device *adev, const struct amba_id *id)
+{
+	struct device_node *of_node = adev->dev.of_node;
+	const struct of_device_id *match = NULL;
+	struct pl353_smc_data *pl353_smc;
+
+	pl353_smc = devm_kzalloc(&adev->dev, sizeof(*pl353_smc), GFP_KERNEL);
+	if (!pl353_smc)
+		return -ENOMEM;
+
+	pl353_smc->aclk = devm_clk_get_enabled(&adev->dev, "apb_pclk");
+	if (IS_ERR(pl353_smc->aclk))
+		return dev_err_probe(&adev->dev, PTR_ERR(pl353_smc->aclk),
+				     "aclk clock not found.\n");
+
+	pl353_smc->memclk = devm_clk_get_enabled(&adev->dev, "memclk");
+	if (IS_ERR(pl353_smc->memclk))
+		return dev_err_probe(&adev->dev, PTR_ERR(pl353_smc->memclk),
+				     "memclk clock not found.\n");
+
+	amba_set_drvdata(adev, pl353_smc);
+
+	/* Find compatible children. Only a single child is supported */
+	for_each_available_child_of_node_scoped(of_node, child) {
+		match = of_match_node(pl353_smc_supported_children, child);
+		if (!match) {
+			dev_warn(&adev->dev, "unsupported child node\n");
+			continue;
+		}
+		of_platform_device_create(child, NULL, &adev->dev);
+		break;
+	}
+	if (!match) {
+		dev_err(&adev->dev, "no matching children\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+static const struct amba_id pl353_ids[] = {
+	{
+		.id = 0x00041353,
+		.mask = 0x000fffff,
+	},
+	{ 0, 0 },
+};
+MODULE_DEVICE_TABLE(amba, pl353_ids);
+
+static struct amba_driver pl353_smc_driver = {
+	.drv = {
+		.name = "pl353-smc",
+		.pm = &pl353_smc_dev_pm_ops,
+	},
+	.id_table = pl353_ids,
+	.probe = pl353_smc_probe,
+};
+
+module_amba_driver(pl353_smc_driver);
+
+MODULE_AUTHOR("Xilinx, Inc.");
+MODULE_DESCRIPTION("ARM PL353 SMC Driver");
+MODULE_LICENSE("GPL");