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>

3 files changed, 215 insertions, 0 deletions

diff --git a/drivers/interconnect/samsung/Kconfig b/drivers/interconnect/samsung/Kconfig
new file mode 100644
index 000000000..fbee87e37
--- /dev/null
+++ b/drivers/interconnect/samsung/Kconfig
@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config INTERCONNECT_SAMSUNG
+	bool "Samsung SoC interconnect drivers"
+	depends on ARCH_EXYNOS || COMPILE_TEST
+	help
+	  Interconnect drivers for Samsung SoCs.
+
+config INTERCONNECT_EXYNOS
+	tristate "Exynos SoC generic interconnect driver"
+	depends on INTERCONNECT_SAMSUNG
+	default y if ARCH_EXYNOS
+	help
+	  Generic interconnect driver for Samsung Exynos SoCs (e.g. Exynos3250,
+	  Exynos4210, Exynos4412, Exynos542x, Exynos5433).
+	  Choose Y here only if you build for such Samsung SoC.
diff --git a/drivers/interconnect/samsung/Makefile b/drivers/interconnect/samsung/Makefile
new file mode 100644
index 000000000..e19d1df7d
--- /dev/null
+++ b/drivers/interconnect/samsung/Makefile
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
+exynos-interconnect-objs		:= exynos.o
+
+obj-$(CONFIG_INTERCONNECT_EXYNOS)	+= exynos-interconnect.o
diff --git a/drivers/interconnect/samsung/exynos.c b/drivers/interconnect/samsung/exynos.c
new file mode 100644
index 000000000..8e8f56186
--- /dev/null
+++ b/drivers/interconnect/samsung/exynos.c
@@ -0,0 +1,196 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Exynos generic interconnect provider driver
+ *
+ * Copyright (c) 2020 Samsung Electronics Co., Ltd.
+ *
+ * Authors: Artur Świgoń <a.swigon@samsung.com>
+ *          Sylwester Nawrocki <s.nawrocki@samsung.com>
+ */
+#include <linux/device.h>
+#include <linux/interconnect-provider.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/pm_qos.h>
+#include <linux/slab.h>
+
+#define EXYNOS_ICC_DEFAULT_BUS_CLK_RATIO	8
+
+struct exynos_icc_priv {
+	struct device *dev;
+
+	/* One interconnect node per provider */
+	struct icc_provider provider;
+	struct icc_node *node;
+
+	struct dev_pm_qos_request qos_req;
+	u32 bus_clk_ratio;
+};
+
+static struct icc_node *exynos_icc_get_parent(struct device_node *np)
+{
+	struct of_phandle_args args;
+	struct icc_node_data *icc_node_data;
+	struct icc_node *icc_node;
+	int num, ret;
+
+	num = of_count_phandle_with_args(np, "interconnects",
+					 "#interconnect-cells");
+	if (num < 1)
+		return NULL; /* parent nodes are optional */
+
+	/* Get the interconnect target node */
+	ret = of_parse_phandle_with_args(np, "interconnects",
+					"#interconnect-cells", 0, &args);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
+	icc_node_data = of_icc_get_from_provider(&args);
+	of_node_put(args.np);
+
+	if (IS_ERR(icc_node_data))
+		return ERR_CAST(icc_node_data);
+
+	icc_node = icc_node_data->node;
+	kfree(icc_node_data);
+
+	return icc_node;
+}
+
+static int exynos_generic_icc_set(struct icc_node *src, struct icc_node *dst)
+{
+	struct exynos_icc_priv *src_priv = src->data, *dst_priv = dst->data;
+	s32 src_freq = max(src->avg_bw, src->peak_bw) / src_priv->bus_clk_ratio;
+	s32 dst_freq = max(dst->avg_bw, dst->peak_bw) / dst_priv->bus_clk_ratio;
+	int ret;
+
+	ret = dev_pm_qos_update_request(&src_priv->qos_req, src_freq);
+	if (ret < 0) {
+		dev_err(src_priv->dev, "failed to update PM QoS of %s (src)\n",
+			src->name);
+		return ret;
+	}
+
+	ret = dev_pm_qos_update_request(&dst_priv->qos_req, dst_freq);
+	if (ret < 0) {
+		dev_err(dst_priv->dev, "failed to update PM QoS of %s (dst)\n",
+			dst->name);
+		return ret;
+	}
+
+	return 0;
+}
+
+static struct icc_node *exynos_generic_icc_xlate(const struct of_phandle_args *spec,
+						 void *data)
+{
+	struct exynos_icc_priv *priv = data;
+
+	if (spec->np != priv->dev->parent->of_node)
+		return ERR_PTR(-EINVAL);
+
+	return priv->node;
+}
+
+static void exynos_generic_icc_remove(struct platform_device *pdev)
+{
+	struct exynos_icc_priv *priv = platform_get_drvdata(pdev);
+
+	icc_provider_deregister(&priv->provider);
+	icc_nodes_remove(&priv->provider);
+}
+
+static int exynos_generic_icc_probe(struct platform_device *pdev)
+{
+	struct device *bus_dev = pdev->dev.parent;
+	struct exynos_icc_priv *priv;
+	struct icc_provider *provider;
+	struct icc_node *icc_node, *icc_parent_node;
+	int ret;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->dev = &pdev->dev;
+	platform_set_drvdata(pdev, priv);
+
+	provider = &priv->provider;
+
+	provider->set = exynos_generic_icc_set;
+	provider->aggregate = icc_std_aggregate;
+	provider->xlate = exynos_generic_icc_xlate;
+	provider->dev = bus_dev;
+	provider->inter_set = true;
+	provider->data = priv;
+
+	icc_provider_init(provider);
+
+	icc_node = icc_node_create(pdev->id);
+	if (IS_ERR(icc_node))
+		return PTR_ERR(icc_node);
+
+	priv->node = icc_node;
+	icc_node->name = devm_kasprintf(&pdev->dev, GFP_KERNEL, "%pOFn",
+					bus_dev->of_node);
+	if (!icc_node->name) {
+		icc_node_destroy(pdev->id);
+		return -ENOMEM;
+	}
+
+	if (of_property_read_u32(bus_dev->of_node, "samsung,data-clock-ratio",
+				 &priv->bus_clk_ratio))
+		priv->bus_clk_ratio = EXYNOS_ICC_DEFAULT_BUS_CLK_RATIO;
+
+	icc_node->data = priv;
+	icc_node_add(icc_node, provider);
+
+	/*
+	 * Register a PM QoS request for the parent (devfreq) device.
+	 */
+	ret = dev_pm_qos_add_request(bus_dev, &priv->qos_req,
+				     DEV_PM_QOS_MIN_FREQUENCY, 0);
+	if (ret < 0)
+		goto err_node_del;
+
+	icc_parent_node = exynos_icc_get_parent(bus_dev->of_node);
+	if (IS_ERR(icc_parent_node)) {
+		ret = PTR_ERR(icc_parent_node);
+		goto err_pmqos_del;
+	}
+	if (icc_parent_node) {
+		ret = icc_link_create(icc_node, icc_parent_node->id);
+		if (ret < 0)
+			goto err_pmqos_del;
+	}
+
+	ret = icc_provider_register(provider);
+	if (ret < 0)
+		goto err_pmqos_del;
+
+	return 0;
+
+err_pmqos_del:
+	dev_pm_qos_remove_request(&priv->qos_req);
+err_node_del:
+	icc_nodes_remove(provider);
+
+	return ret;
+}
+
+static struct platform_driver exynos_generic_icc_driver = {
+	.driver = {
+		.name = "exynos-generic-icc",
+		.sync_state = icc_sync_state,
+	},
+	.probe = exynos_generic_icc_probe,
+	.remove = exynos_generic_icc_remove,
+};
+module_platform_driver(exynos_generic_icc_driver);
+
+MODULE_DESCRIPTION("Exynos generic interconnect driver");
+MODULE_AUTHOR("Artur Świgoń <a.swigon@samsung.com>");
+MODULE_AUTHOR("Sylwester Nawrocki <s.nawrocki@samsung.com>");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:exynos-generic-icc");