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/mfd/ac100.c b/drivers/mfd/ac100.c
new file mode 100644
index 000000000..8f47c392c
--- /dev/null
+++ b/drivers/mfd/ac100.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * MFD core driver for X-Powers' AC100 Audio Codec IC
+ *
+ * The AC100 is a highly integrated audio codec and RTC subsystem designed
+ * for mobile applications. It has 3 I2S/PCM interfaces, a 2 channel DAC,
+ * a 2 channel ADC with 5 inputs and a builtin mixer. The RTC subsystem has
+ * 3 clock outputs.
+ *
+ * The audio codec and RTC parts are completely separate, sharing only the
+ * host interface for access to its registers.
+ *
+ * Copyright (2016) Chen-Yu Tsai
+ *
+ * Author: Chen-Yu Tsai <wens@csie.org>
+ */
+
+#include <linux/interrupt.h>
+#include <linux/kernel.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/ac100.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+#include <linux/sunxi-rsb.h>
+
+static const struct regmap_range ac100_writeable_ranges[] = {
+	regmap_reg_range(AC100_CHIP_AUDIO_RST, AC100_I2S_SR_CTRL),
+	regmap_reg_range(AC100_I2S1_CLK_CTRL, AC100_I2S1_MXR_GAIN),
+	regmap_reg_range(AC100_I2S2_CLK_CTRL, AC100_I2S2_MXR_GAIN),
+	regmap_reg_range(AC100_I2S3_CLK_CTRL, AC100_I2S3_SIG_PATH_CTRL),
+	regmap_reg_range(AC100_ADC_DIG_CTRL, AC100_ADC_VOL_CTRL),
+	regmap_reg_range(AC100_HMIC_CTRL1, AC100_HMIC_STATUS),
+	regmap_reg_range(AC100_DAC_DIG_CTRL, AC100_DAC_MXR_GAIN),
+	regmap_reg_range(AC100_ADC_APC_CTRL, AC100_LINEOUT_CTRL),
+	regmap_reg_range(AC100_ADC_DAP_L_CTRL, AC100_ADC_DAP_OPT),
+	regmap_reg_range(AC100_DAC_DAP_CTRL, AC100_DAC_DAP_OPT),
+	regmap_reg_range(AC100_ADC_DAP_ENA, AC100_DAC_DAP_ENA),
+	regmap_reg_range(AC100_SRC1_CTRL1, AC100_SRC1_CTRL2),
+	regmap_reg_range(AC100_SRC2_CTRL1, AC100_SRC2_CTRL2),
+	regmap_reg_range(AC100_CLK32K_ANALOG_CTRL, AC100_CLKOUT_CTRL3),
+	regmap_reg_range(AC100_RTC_RST, AC100_RTC_UPD),
+	regmap_reg_range(AC100_ALM_INT_ENA, AC100_ALM_INT_STA),
+	regmap_reg_range(AC100_ALM_SEC, AC100_RTC_GP(15)),
+};
+
+static const struct regmap_range ac100_volatile_ranges[] = {
+	regmap_reg_range(AC100_CHIP_AUDIO_RST, AC100_PLL_CTRL2),
+	regmap_reg_range(AC100_HMIC_STATUS, AC100_HMIC_STATUS),
+	regmap_reg_range(AC100_ADC_DAP_L_STA, AC100_ADC_DAP_L_STA),
+	regmap_reg_range(AC100_SRC1_CTRL1, AC100_SRC1_CTRL1),
+	regmap_reg_range(AC100_SRC1_CTRL3, AC100_SRC2_CTRL1),
+	regmap_reg_range(AC100_SRC2_CTRL3, AC100_SRC2_CTRL4),
+	regmap_reg_range(AC100_RTC_RST, AC100_RTC_RST),
+	regmap_reg_range(AC100_RTC_SEC, AC100_ALM_INT_STA),
+	regmap_reg_range(AC100_ALM_SEC, AC100_ALM_UPD),
+};
+
+static const struct regmap_access_table ac100_writeable_table = {
+	.yes_ranges	= ac100_writeable_ranges,
+	.n_yes_ranges	= ARRAY_SIZE(ac100_writeable_ranges),
+};
+
+static const struct regmap_access_table ac100_volatile_table = {
+	.yes_ranges	= ac100_volatile_ranges,
+	.n_yes_ranges	= ARRAY_SIZE(ac100_volatile_ranges),
+};
+
+static const struct regmap_config ac100_regmap_config = {
+	.reg_bits	= 8,
+	.val_bits	= 16,
+	.wr_table	= &ac100_writeable_table,
+	.volatile_table	= &ac100_volatile_table,
+	.max_register	= AC100_RTC_GP(15),
+	.cache_type	= REGCACHE_MAPLE,
+};
+
+static struct mfd_cell ac100_cells[] = {
+	{
+		.name		= "ac100-codec",
+		.of_compatible	= "x-powers,ac100-codec",
+	}, {
+		.name		= "ac100-rtc",
+		.of_compatible	= "x-powers,ac100-rtc",
+	},
+};
+
+static int ac100_rsb_probe(struct sunxi_rsb_device *rdev)
+{
+	struct ac100_dev *ac100;
+	int ret;
+
+	ac100 = devm_kzalloc(&rdev->dev, sizeof(*ac100), GFP_KERNEL);
+	if (!ac100)
+		return -ENOMEM;
+
+	ac100->dev = &rdev->dev;
+	sunxi_rsb_device_set_drvdata(rdev, ac100);
+
+	ac100->regmap = devm_regmap_init_sunxi_rsb(rdev, &ac100_regmap_config);
+	if (IS_ERR(ac100->regmap)) {
+		ret = PTR_ERR(ac100->regmap);
+		dev_err(ac100->dev, "regmap init failed: %d\n", ret);
+		return ret;
+	}
+
+	ret = devm_mfd_add_devices(ac100->dev, PLATFORM_DEVID_NONE, ac100_cells,
+				   ARRAY_SIZE(ac100_cells), NULL, 0, NULL);
+	if (ret) {
+		dev_err(ac100->dev, "failed to add MFD devices: %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+static const struct of_device_id ac100_of_match[] = {
+	{ .compatible = "x-powers,ac100" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, ac100_of_match);
+
+static struct sunxi_rsb_driver ac100_rsb_driver = {
+	.driver = {
+		.name	= "ac100",
+		.of_match_table	= of_match_ptr(ac100_of_match),
+	},
+	.probe	= ac100_rsb_probe,
+};
+module_sunxi_rsb_driver(ac100_rsb_driver);
+
+MODULE_DESCRIPTION("Audio codec MFD core driver for AC100");
+MODULE_AUTHOR("Chen-Yu Tsai <wens@csie.org>");
+MODULE_LICENSE("GPL v2");