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, 276 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-rp5c01.c b/drivers/rtc/rtc-rp5c01.c
new file mode 100644
index 000000000..44afa6d99
--- /dev/null
+++ b/drivers/rtc/rtc-rp5c01.c
@@ -0,0 +1,276 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Ricoh RP5C01 RTC Driver
+ *
+ *  Copyright 2009 Geert Uytterhoeven
+ *
+ *  Based on the A3000 TOD code in arch/m68k/amiga/config.c
+ *  Copyright (C) 1993 Hamish Macdonald
+ */
+
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/slab.h>
+
+
+enum {
+	RP5C01_1_SECOND		= 0x0,	/* MODE 00 */
+	RP5C01_10_SECOND	= 0x1,	/* MODE 00 */
+	RP5C01_1_MINUTE		= 0x2,	/* MODE 00 and MODE 01 */
+	RP5C01_10_MINUTE	= 0x3,	/* MODE 00 and MODE 01 */
+	RP5C01_1_HOUR		= 0x4,	/* MODE 00 and MODE 01 */
+	RP5C01_10_HOUR		= 0x5,	/* MODE 00 and MODE 01 */
+	RP5C01_DAY_OF_WEEK	= 0x6,	/* MODE 00 and MODE 01 */
+	RP5C01_1_DAY		= 0x7,	/* MODE 00 and MODE 01 */
+	RP5C01_10_DAY		= 0x8,	/* MODE 00 and MODE 01 */
+	RP5C01_1_MONTH		= 0x9,	/* MODE 00 */
+	RP5C01_10_MONTH		= 0xa,	/* MODE 00 */
+	RP5C01_1_YEAR		= 0xb,	/* MODE 00 */
+	RP5C01_10_YEAR		= 0xc,	/* MODE 00 */
+
+	RP5C01_12_24_SELECT	= 0xa,	/* MODE 01 */
+	RP5C01_LEAP_YEAR	= 0xb,	/* MODE 01 */
+
+	RP5C01_MODE		= 0xd,	/* all modes */
+	RP5C01_TEST		= 0xe,	/* all modes */
+	RP5C01_RESET		= 0xf,	/* all modes */
+};
+
+#define RP5C01_12_24_SELECT_12	(0 << 0)
+#define RP5C01_12_24_SELECT_24	(1 << 0)
+
+#define RP5C01_10_HOUR_AM	(0 << 1)
+#define RP5C01_10_HOUR_PM	(1 << 1)
+
+#define RP5C01_MODE_TIMER_EN	(1 << 3)	/* timer enable */
+#define RP5C01_MODE_ALARM_EN	(1 << 2)	/* alarm enable */
+
+#define RP5C01_MODE_MODE_MASK	(3 << 0)
+#define RP5C01_MODE_MODE00	(0 << 0)	/* time */
+#define RP5C01_MODE_MODE01	(1 << 0)	/* alarm, 12h/24h, leap year */
+#define RP5C01_MODE_RAM_BLOCK10	(2 << 0)	/* RAM 4 bits x 13 */
+#define RP5C01_MODE_RAM_BLOCK11	(3 << 0)	/* RAM 4 bits x 13 */
+
+#define RP5C01_RESET_1HZ_PULSE	(1 << 3)
+#define RP5C01_RESET_16HZ_PULSE	(1 << 2)
+#define RP5C01_RESET_SECOND	(1 << 1)	/* reset divider stages for */
+						/* seconds or smaller units */
+#define RP5C01_RESET_ALARM	(1 << 0)	/* reset all alarm registers */
+
+
+struct rp5c01_priv {
+	u32 __iomem *regs;
+	struct rtc_device *rtc;
+	spinlock_t lock;	/* against concurrent RTC/NVRAM access */
+};
+
+static inline unsigned int rp5c01_read(struct rp5c01_priv *priv,
+				       unsigned int reg)
+{
+	return __raw_readl(&priv->regs[reg]) & 0xf;
+}
+
+static inline void rp5c01_write(struct rp5c01_priv *priv, unsigned int val,
+				unsigned int reg)
+{
+	__raw_writel(val, &priv->regs[reg]);
+}
+
+static void rp5c01_lock(struct rp5c01_priv *priv)
+{
+	rp5c01_write(priv, RP5C01_MODE_MODE00, RP5C01_MODE);
+}
+
+static void rp5c01_unlock(struct rp5c01_priv *priv)
+{
+	rp5c01_write(priv, RP5C01_MODE_TIMER_EN | RP5C01_MODE_MODE01,
+		     RP5C01_MODE);
+}
+
+static int rp5c01_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rp5c01_priv *priv = dev_get_drvdata(dev);
+
+	spin_lock_irq(&priv->lock);
+	rp5c01_lock(priv);
+
+	tm->tm_sec  = rp5c01_read(priv, RP5C01_10_SECOND) * 10 +
+		      rp5c01_read(priv, RP5C01_1_SECOND);
+	tm->tm_min  = rp5c01_read(priv, RP5C01_10_MINUTE) * 10 +
+		      rp5c01_read(priv, RP5C01_1_MINUTE);
+	tm->tm_hour = rp5c01_read(priv, RP5C01_10_HOUR) * 10 +
+		      rp5c01_read(priv, RP5C01_1_HOUR);
+	tm->tm_mday = rp5c01_read(priv, RP5C01_10_DAY) * 10 +
+		      rp5c01_read(priv, RP5C01_1_DAY);
+	tm->tm_wday = rp5c01_read(priv, RP5C01_DAY_OF_WEEK);
+	tm->tm_mon  = rp5c01_read(priv, RP5C01_10_MONTH) * 10 +
+		      rp5c01_read(priv, RP5C01_1_MONTH) - 1;
+	tm->tm_year = rp5c01_read(priv, RP5C01_10_YEAR) * 10 +
+		      rp5c01_read(priv, RP5C01_1_YEAR);
+	if (tm->tm_year <= 69)
+		tm->tm_year += 100;
+
+	rp5c01_unlock(priv);
+	spin_unlock_irq(&priv->lock);
+
+	return 0;
+}
+
+static int rp5c01_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rp5c01_priv *priv = dev_get_drvdata(dev);
+
+	spin_lock_irq(&priv->lock);
+	rp5c01_lock(priv);
+
+	rp5c01_write(priv, tm->tm_sec / 10, RP5C01_10_SECOND);
+	rp5c01_write(priv, tm->tm_sec % 10, RP5C01_1_SECOND);
+	rp5c01_write(priv, tm->tm_min / 10, RP5C01_10_MINUTE);
+	rp5c01_write(priv, tm->tm_min % 10, RP5C01_1_MINUTE);
+	rp5c01_write(priv, tm->tm_hour / 10, RP5C01_10_HOUR);
+	rp5c01_write(priv, tm->tm_hour % 10, RP5C01_1_HOUR);
+	rp5c01_write(priv, tm->tm_mday / 10, RP5C01_10_DAY);
+	rp5c01_write(priv, tm->tm_mday % 10, RP5C01_1_DAY);
+	if (tm->tm_wday != -1)
+		rp5c01_write(priv, tm->tm_wday, RP5C01_DAY_OF_WEEK);
+	rp5c01_write(priv, (tm->tm_mon + 1) / 10, RP5C01_10_MONTH);
+	rp5c01_write(priv, (tm->tm_mon + 1) % 10, RP5C01_1_MONTH);
+	if (tm->tm_year >= 100)
+		tm->tm_year -= 100;
+	rp5c01_write(priv, tm->tm_year / 10, RP5C01_10_YEAR);
+	rp5c01_write(priv, tm->tm_year % 10, RP5C01_1_YEAR);
+
+	rp5c01_unlock(priv);
+	spin_unlock_irq(&priv->lock);
+	return 0;
+}
+
+static const struct rtc_class_ops rp5c01_rtc_ops = {
+	.read_time	= rp5c01_read_time,
+	.set_time	= rp5c01_set_time,
+};
+
+
+/*
+ * The NVRAM is organized as 2 blocks of 13 nibbles of 4 bits.
+ * We provide access to them like AmigaOS does: the high nibble of each 8-bit
+ * byte is stored in BLOCK10, the low nibble in BLOCK11.
+ */
+
+static int rp5c01_nvram_read(void *_priv, unsigned int pos, void *val,
+			     size_t bytes)
+{
+	struct rp5c01_priv *priv = _priv;
+	u8 *buf = val;
+
+	spin_lock_irq(&priv->lock);
+
+	for (; bytes; bytes--) {
+		u8 data;
+
+		rp5c01_write(priv,
+			     RP5C01_MODE_TIMER_EN | RP5C01_MODE_RAM_BLOCK10,
+			     RP5C01_MODE);
+		data = rp5c01_read(priv, pos) << 4;
+		rp5c01_write(priv,
+			     RP5C01_MODE_TIMER_EN | RP5C01_MODE_RAM_BLOCK11,
+			     RP5C01_MODE);
+		data |= rp5c01_read(priv, pos++);
+		rp5c01_write(priv, RP5C01_MODE_TIMER_EN | RP5C01_MODE_MODE01,
+			     RP5C01_MODE);
+		*buf++ = data;
+	}
+
+	spin_unlock_irq(&priv->lock);
+	return 0;
+}
+
+static int rp5c01_nvram_write(void *_priv, unsigned int pos, void *val,
+			      size_t bytes)
+{
+	struct rp5c01_priv *priv = _priv;
+	u8 *buf = val;
+
+	spin_lock_irq(&priv->lock);
+
+	for (; bytes; bytes--) {
+		u8 data = *buf++;
+
+		rp5c01_write(priv,
+			     RP5C01_MODE_TIMER_EN | RP5C01_MODE_RAM_BLOCK10,
+			     RP5C01_MODE);
+		rp5c01_write(priv, data >> 4, pos);
+		rp5c01_write(priv,
+			     RP5C01_MODE_TIMER_EN | RP5C01_MODE_RAM_BLOCK11,
+			     RP5C01_MODE);
+		rp5c01_write(priv, data & 0xf, pos++);
+		rp5c01_write(priv, RP5C01_MODE_TIMER_EN | RP5C01_MODE_MODE01,
+			     RP5C01_MODE);
+	}
+
+	spin_unlock_irq(&priv->lock);
+	return 0;
+}
+
+static int __init rp5c01_rtc_probe(struct platform_device *dev)
+{
+	struct resource *res;
+	struct rp5c01_priv *priv;
+	struct rtc_device *rtc;
+	int error;
+	struct nvmem_config nvmem_cfg = {
+		.name = "rp5c01_nvram",
+		.word_size = 1,
+		.stride = 1,
+		.size = RP5C01_MODE,
+		.reg_read = rp5c01_nvram_read,
+		.reg_write = rp5c01_nvram_write,
+	};
+
+	res = platform_get_resource(dev, IORESOURCE_MEM, 0);
+	if (!res)
+		return -ENODEV;
+
+	priv = devm_kzalloc(&dev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->regs = devm_ioremap(&dev->dev, res->start, resource_size(res));
+	if (!priv->regs)
+		return -ENOMEM;
+
+	spin_lock_init(&priv->lock);
+
+	platform_set_drvdata(dev, priv);
+
+	rtc = devm_rtc_allocate_device(&dev->dev);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	rtc->ops = &rp5c01_rtc_ops;
+
+	priv->rtc = rtc;
+
+	nvmem_cfg.priv = priv;
+	error = devm_rtc_nvmem_register(rtc, &nvmem_cfg);
+	if (error)
+		return error;
+
+	return devm_rtc_register_device(rtc);
+}
+
+static struct platform_driver rp5c01_rtc_driver = {
+	.driver	= {
+		.name	= "rtc-rp5c01",
+	},
+};
+
+module_platform_driver_probe(rp5c01_rtc_driver, rp5c01_rtc_probe);
+
+MODULE_AUTHOR("Geert Uytterhoeven <geert@linux-m68k.org>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Ricoh RP5C01 RTC driver");
+MODULE_ALIAS("platform:rtc-rp5c01");