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, 161 insertions, 0 deletions

diff --git a/drivers/soc/tegra/common.c b/drivers/soc/tegra/common.c
new file mode 100644
index 000000000..0864eb018
--- /dev/null
+++ b/drivers/soc/tegra/common.c
@@ -0,0 +1,161 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2014 NVIDIA CORPORATION.  All rights reserved.
+ */
+
+#define dev_fmt(fmt)	"tegra-soc: " fmt
+
+#include <linux/clk.h>
+#include <linux/device.h>
+#include <linux/export.h>
+#include <linux/of.h>
+#include <linux/pm_opp.h>
+#include <linux/pm_runtime.h>
+
+#include <soc/tegra/common.h>
+#include <soc/tegra/fuse.h>
+
+static const struct of_device_id tegra_machine_match[] = {
+	{ .compatible = "nvidia,tegra20", },
+	{ .compatible = "nvidia,tegra30", },
+	{ .compatible = "nvidia,tegra114", },
+	{ .compatible = "nvidia,tegra124", },
+	{ .compatible = "nvidia,tegra132", },
+	{ .compatible = "nvidia,tegra210", },
+	{ }
+};
+
+bool soc_is_tegra(void)
+{
+	return of_machine_device_match(tegra_machine_match);
+}
+
+static int tegra_core_dev_init_opp_state(struct device *dev)
+{
+	unsigned long rate;
+	struct clk *clk;
+	bool rpm_enabled;
+	int err;
+
+	clk = devm_clk_get(dev, NULL);
+	if (IS_ERR(clk)) {
+		dev_err(dev, "failed to get clk: %pe\n", clk);
+		return PTR_ERR(clk);
+	}
+
+	rate = clk_get_rate(clk);
+	if (!rate) {
+		dev_err(dev, "failed to get clk rate\n");
+		return -EINVAL;
+	}
+
+	/*
+	 * Runtime PM of the device must be enabled in order to set up
+	 * GENPD's performance properly because GENPD core checks whether
+	 * device is suspended and this check doesn't work while RPM is
+	 * disabled. This makes sure the OPP vote below gets cached in
+	 * GENPD for the device. Instead, the vote is done the next time
+	 * the device gets runtime resumed.
+	 */
+	rpm_enabled = pm_runtime_enabled(dev);
+	if (!rpm_enabled)
+		pm_runtime_enable(dev);
+
+	/* should never happen in practice */
+	if (!pm_runtime_enabled(dev)) {
+		dev_WARN(dev, "failed to enable runtime PM\n");
+		pm_runtime_disable(dev);
+		return -EINVAL;
+	}
+
+	/* first dummy rate-setting initializes voltage vote */
+	err = dev_pm_opp_set_rate(dev, rate);
+
+	if (!rpm_enabled)
+		pm_runtime_disable(dev);
+
+	if (err) {
+		dev_err(dev, "failed to initialize OPP clock: %d\n", err);
+		return err;
+	}
+
+	return 0;
+}
+
+/**
+ * devm_tegra_core_dev_init_opp_table() - initialize OPP table
+ * @dev: device for which OPP table is initialized
+ * @params: pointer to the OPP table configuration
+ *
+ * This function will initialize OPP table and sync OPP state of a Tegra SoC
+ * core device.
+ *
+ * Return: 0 on success or errorno.
+ */
+int devm_tegra_core_dev_init_opp_table(struct device *dev,
+				       struct tegra_core_opp_params *params)
+{
+	u32 hw_version;
+	int err;
+	/*
+	 * The clk's connection id to set is NULL and this is a NULL terminated
+	 * array, hence two NULL entries.
+	 */
+	const char *clk_names[] = { NULL, NULL };
+	struct dev_pm_opp_config config = {
+		/*
+		 * For some devices we don't have any OPP table in the DT, and
+		 * in order to use the same code path for all the devices, we
+		 * create a dummy OPP table for them via this. The dummy OPP
+		 * table is only capable of doing clk_set_rate() on invocation
+		 * of dev_pm_opp_set_rate() and doesn't provide any other
+		 * functionality.
+		 */
+		.clk_names = clk_names,
+	};
+
+	if (of_machine_is_compatible("nvidia,tegra20")) {
+		hw_version = BIT(tegra_sku_info.soc_process_id);
+		config.supported_hw = &hw_version;
+		config.supported_hw_count = 1;
+	} else if (of_machine_is_compatible("nvidia,tegra30") ||
+		   of_machine_is_compatible("nvidia,tegra114")) {
+		hw_version = BIT(tegra_sku_info.soc_speedo_id);
+		config.supported_hw = &hw_version;
+		config.supported_hw_count = 1;
+	}
+
+	err = devm_pm_opp_set_config(dev, &config);
+	if (err) {
+		dev_err(dev, "failed to set OPP config: %d\n", err);
+		return err;
+	}
+
+	/*
+	 * Tegra124+ doesn't support OPP yet, return early for pre-Tegra124
+	 * case.
+	 */
+	if (!config.supported_hw)
+		return -ENODEV;
+
+	/*
+	 * Older device-trees have an empty OPP table, we will get
+	 * -ENODEV from devm_pm_opp_of_add_table() in this case.
+	 */
+	err = devm_pm_opp_of_add_table(dev);
+	if (err) {
+		if (err != -ENODEV)
+			dev_err(dev, "failed to add OPP table: %d\n", err);
+
+		return err;
+	}
+
+	if (params->init_state) {
+		err = tegra_core_dev_init_opp_state(dev);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(devm_tegra_core_dev_init_opp_table);