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, 279 insertions, 0 deletions

diff --git a/drivers/misc/atmel-ssc.c b/drivers/misc/atmel-ssc.c
new file mode 100644
index 000000000..35a196341
--- /dev/null
+++ b/drivers/misc/atmel-ssc.c
@@ -0,0 +1,279 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Atmel SSC driver
+ *
+ * Copyright (C) 2007 Atmel Corporation
+ */
+
+#include <linux/platform_device.h>
+#include <linux/list.h>
+#include <linux/clk.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/mutex.h>
+#include <linux/atmel-ssc.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+
+#include <linux/of.h>
+
+#include "../../sound/soc/atmel/atmel_ssc_dai.h"
+
+/* Serialize access to ssc_list and user count */
+static DEFINE_MUTEX(user_lock);
+static LIST_HEAD(ssc_list);
+
+struct ssc_device *ssc_request(unsigned int ssc_num)
+{
+	int ssc_valid = 0;
+	struct ssc_device *ssc;
+
+	mutex_lock(&user_lock);
+	list_for_each_entry(ssc, &ssc_list, list) {
+		if (ssc->pdev->dev.of_node) {
+			if (of_alias_get_id(ssc->pdev->dev.of_node, "ssc")
+				== ssc_num) {
+				ssc->pdev->id = ssc_num;
+				ssc_valid = 1;
+				break;
+			}
+		} else if (ssc->pdev->id == ssc_num) {
+			ssc_valid = 1;
+			break;
+		}
+	}
+
+	if (!ssc_valid) {
+		mutex_unlock(&user_lock);
+		pr_err("ssc: ssc%d platform device is missing\n", ssc_num);
+		return ERR_PTR(-ENODEV);
+	}
+
+	if (ssc->user) {
+		mutex_unlock(&user_lock);
+		dev_dbg(&ssc->pdev->dev, "module busy\n");
+		return ERR_PTR(-EBUSY);
+	}
+	ssc->user++;
+	mutex_unlock(&user_lock);
+
+	clk_prepare(ssc->clk);
+
+	return ssc;
+}
+EXPORT_SYMBOL(ssc_request);
+
+void ssc_free(struct ssc_device *ssc)
+{
+	bool disable_clk = true;
+
+	mutex_lock(&user_lock);
+	if (ssc->user)
+		ssc->user--;
+	else {
+		disable_clk = false;
+		dev_dbg(&ssc->pdev->dev, "device already free\n");
+	}
+	mutex_unlock(&user_lock);
+
+	if (disable_clk)
+		clk_unprepare(ssc->clk);
+}
+EXPORT_SYMBOL(ssc_free);
+
+static struct atmel_ssc_platform_data at91rm9200_config = {
+	.use_dma = 0,
+	.has_fslen_ext = 0,
+};
+
+static struct atmel_ssc_platform_data at91sam9rl_config = {
+	.use_dma = 0,
+	.has_fslen_ext = 1,
+};
+
+static struct atmel_ssc_platform_data at91sam9g45_config = {
+	.use_dma = 1,
+	.has_fslen_ext = 1,
+};
+
+static const struct platform_device_id atmel_ssc_devtypes[] = {
+	{
+		.name = "at91rm9200_ssc",
+		.driver_data = (unsigned long) &at91rm9200_config,
+	}, {
+		.name = "at91sam9rl_ssc",
+		.driver_data = (unsigned long) &at91sam9rl_config,
+	}, {
+		.name = "at91sam9g45_ssc",
+		.driver_data = (unsigned long) &at91sam9g45_config,
+	}, {
+		/* sentinel */
+	}
+};
+
+#ifdef CONFIG_OF
+static const struct of_device_id atmel_ssc_dt_ids[] = {
+	{
+		.compatible = "atmel,at91rm9200-ssc",
+		.data = &at91rm9200_config,
+	}, {
+		.compatible = "atmel,at91sam9rl-ssc",
+		.data = &at91sam9rl_config,
+	}, {
+		.compatible = "atmel,at91sam9g45-ssc",
+		.data = &at91sam9g45_config,
+	}, {
+		/* sentinel */
+	}
+};
+MODULE_DEVICE_TABLE(of, atmel_ssc_dt_ids);
+#endif
+
+static inline const struct atmel_ssc_platform_data *
+	atmel_ssc_get_driver_data(struct platform_device *pdev)
+{
+	if (pdev->dev.of_node) {
+		const struct of_device_id *match;
+		match = of_match_node(atmel_ssc_dt_ids, pdev->dev.of_node);
+		if (match == NULL)
+			return NULL;
+		return match->data;
+	}
+
+	return (struct atmel_ssc_platform_data *)
+		platform_get_device_id(pdev)->driver_data;
+}
+
+#ifdef CONFIG_SND_ATMEL_SOC_SSC
+static int ssc_sound_dai_probe(struct ssc_device *ssc)
+{
+	struct device_node *np = ssc->pdev->dev.of_node;
+	int ret;
+	int id;
+
+	ssc->sound_dai = false;
+
+	if (!of_property_present(np, "#sound-dai-cells"))
+		return 0;
+
+	id = of_alias_get_id(np, "ssc");
+	if (id < 0)
+		return id;
+
+	ret = atmel_ssc_set_audio(id);
+	ssc->sound_dai = !ret;
+
+	return ret;
+}
+
+static void ssc_sound_dai_remove(struct ssc_device *ssc)
+{
+	if (!ssc->sound_dai)
+		return;
+
+	atmel_ssc_put_audio(of_alias_get_id(ssc->pdev->dev.of_node, "ssc"));
+}
+#else
+static inline int ssc_sound_dai_probe(struct ssc_device *ssc)
+{
+	if (of_property_present(ssc->pdev->dev.of_node, "#sound-dai-cells"))
+		return -ENOTSUPP;
+
+	return 0;
+}
+
+static inline void ssc_sound_dai_remove(struct ssc_device *ssc)
+{
+}
+#endif
+
+static int ssc_probe(struct platform_device *pdev)
+{
+	struct resource *regs;
+	struct ssc_device *ssc;
+	const struct atmel_ssc_platform_data *plat_dat;
+
+	ssc = devm_kzalloc(&pdev->dev, sizeof(struct ssc_device), GFP_KERNEL);
+	if (!ssc) {
+		dev_dbg(&pdev->dev, "out of memory\n");
+		return -ENOMEM;
+	}
+
+	ssc->pdev = pdev;
+
+	plat_dat = atmel_ssc_get_driver_data(pdev);
+	if (!plat_dat)
+		return -ENODEV;
+	ssc->pdata = (struct atmel_ssc_platform_data *)plat_dat;
+
+	if (pdev->dev.of_node) {
+		struct device_node *np = pdev->dev.of_node;
+		ssc->clk_from_rk_pin =
+			of_property_read_bool(np, "atmel,clk-from-rk-pin");
+	}
+
+	ssc->regs = devm_platform_get_and_ioremap_resource(pdev, 0, &regs);
+	if (IS_ERR(ssc->regs))
+		return PTR_ERR(ssc->regs);
+
+	ssc->phybase = regs->start;
+
+	ssc->clk = devm_clk_get(&pdev->dev, "pclk");
+	if (IS_ERR(ssc->clk)) {
+		dev_dbg(&pdev->dev, "no pclk clock defined\n");
+		return -ENXIO;
+	}
+
+	/* disable all interrupts */
+	clk_prepare_enable(ssc->clk);
+	ssc_writel(ssc->regs, IDR, -1);
+	ssc_readl(ssc->regs, SR);
+	clk_disable_unprepare(ssc->clk);
+
+	ssc->irq = platform_get_irq(pdev, 0);
+	if (ssc->irq < 0) {
+		dev_dbg(&pdev->dev, "could not get irq\n");
+		return ssc->irq;
+	}
+
+	mutex_lock(&user_lock);
+	list_add_tail(&ssc->list, &ssc_list);
+	mutex_unlock(&user_lock);
+
+	platform_set_drvdata(pdev, ssc);
+
+	dev_info(&pdev->dev, "Atmel SSC device at 0x%p (irq %d)\n",
+			ssc->regs, ssc->irq);
+
+	if (ssc_sound_dai_probe(ssc))
+		dev_err(&pdev->dev, "failed to auto-setup ssc for audio\n");
+
+	return 0;
+}
+
+static void ssc_remove(struct platform_device *pdev)
+{
+	struct ssc_device *ssc = platform_get_drvdata(pdev);
+
+	ssc_sound_dai_remove(ssc);
+
+	mutex_lock(&user_lock);
+	list_del(&ssc->list);
+	mutex_unlock(&user_lock);
+}
+
+static struct platform_driver ssc_driver = {
+	.driver		= {
+		.name		= "ssc",
+		.of_match_table	= of_match_ptr(atmel_ssc_dt_ids),
+	},
+	.id_table	= atmel_ssc_devtypes,
+	.probe		= ssc_probe,
+	.remove		= ssc_remove,
+};
+module_platform_driver(ssc_driver);
+
+MODULE_AUTHOR("Hans-Christian Noren Egtvedt <egtvedt@samfundet.no>");
+MODULE_DESCRIPTION("SSC driver for Atmel AT91");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:ssc");