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, 184 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-imx-sc.c b/drivers/rtc/rtc-imx-sc.c
new file mode 100644
index 000000000..814d51664
--- /dev/null
+++ b/drivers/rtc/rtc-imx-sc.c
@@ -0,0 +1,184 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright 2018 NXP.
+ */
+
+#include <dt-bindings/firmware/imx/rsrc.h>
+#include <linux/arm-smccc.h>
+#include <linux/firmware/imx/sci.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+
+#define IMX_SC_TIMER_FUNC_GET_RTC_SEC1970	9
+#define IMX_SC_TIMER_FUNC_SET_RTC_ALARM		8
+#define IMX_SC_TIMER_FUNC_SET_RTC_TIME		6
+
+#define IMX_SIP_SRTC			0xC2000002
+#define IMX_SIP_SRTC_SET_TIME		0x0
+
+#define SC_IRQ_GROUP_RTC    2
+#define SC_IRQ_RTC          1
+
+static struct imx_sc_ipc *rtc_ipc_handle;
+static struct rtc_device *imx_sc_rtc;
+
+struct imx_sc_msg_timer_get_rtc_time {
+	struct imx_sc_rpc_msg hdr;
+	u32 time;
+} __packed;
+
+struct imx_sc_msg_timer_rtc_set_alarm {
+	struct imx_sc_rpc_msg hdr;
+	u16 year;
+	u8 mon;
+	u8 day;
+	u8 hour;
+	u8 min;
+	u8 sec;
+} __packed __aligned(4);
+
+static int imx_sc_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct imx_sc_msg_timer_get_rtc_time msg;
+	struct imx_sc_rpc_msg *hdr = &msg.hdr;
+	int ret;
+
+	hdr->ver = IMX_SC_RPC_VERSION;
+	hdr->svc = IMX_SC_RPC_SVC_TIMER;
+	hdr->func = IMX_SC_TIMER_FUNC_GET_RTC_SEC1970;
+	hdr->size = 1;
+
+	ret = imx_scu_call_rpc(rtc_ipc_handle, &msg, true);
+	if (ret) {
+		dev_err(dev, "read rtc time failed, ret %d\n", ret);
+		return ret;
+	}
+
+	rtc_time64_to_tm(msg.time, tm);
+
+	return 0;
+}
+
+static int imx_sc_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct arm_smccc_res res;
+
+	/* pack 2 time parameters into 1 register, 16 bits for each */
+	arm_smccc_smc(IMX_SIP_SRTC, IMX_SIP_SRTC_SET_TIME,
+		      ((tm->tm_year + 1900) << 16) | (tm->tm_mon + 1),
+		      (tm->tm_mday << 16) | tm->tm_hour,
+		      (tm->tm_min << 16) | tm->tm_sec,
+		      0, 0, 0, &res);
+
+	return res.a0;
+}
+
+static int imx_sc_rtc_alarm_irq_enable(struct device *dev, unsigned int enable)
+{
+	return imx_scu_irq_group_enable(SC_IRQ_GROUP_RTC, SC_IRQ_RTC, enable);
+}
+
+static int imx_sc_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct imx_sc_msg_timer_rtc_set_alarm msg;
+	struct imx_sc_rpc_msg *hdr = &msg.hdr;
+	int ret;
+	struct rtc_time *alrm_tm = &alrm->time;
+
+	hdr->ver = IMX_SC_RPC_VERSION;
+	hdr->svc = IMX_SC_RPC_SVC_TIMER;
+	hdr->func = IMX_SC_TIMER_FUNC_SET_RTC_ALARM;
+	hdr->size = 3;
+
+	msg.year = alrm_tm->tm_year + 1900;
+	msg.mon = alrm_tm->tm_mon + 1;
+	msg.day = alrm_tm->tm_mday;
+	msg.hour = alrm_tm->tm_hour;
+	msg.min = alrm_tm->tm_min;
+	msg.sec = alrm_tm->tm_sec;
+
+	ret = imx_scu_call_rpc(rtc_ipc_handle, &msg, true);
+	if (ret) {
+		dev_err(dev, "set rtc alarm failed, ret %d\n", ret);
+		return ret;
+	}
+
+	ret = imx_sc_rtc_alarm_irq_enable(dev, alrm->enabled);
+	if (ret) {
+		dev_err(dev, "enable rtc alarm failed, ret %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+static const struct rtc_class_ops imx_sc_rtc_ops = {
+	.read_time = imx_sc_rtc_read_time,
+	.set_time = imx_sc_rtc_set_time,
+	.set_alarm = imx_sc_rtc_set_alarm,
+	.alarm_irq_enable = imx_sc_rtc_alarm_irq_enable,
+};
+
+static int imx_sc_rtc_alarm_notify(struct notifier_block *nb,
+					unsigned long event, void *group)
+{
+	/* ignore non-rtc irq */
+	if (!((event & SC_IRQ_RTC) && (*(u8 *)group == SC_IRQ_GROUP_RTC)))
+		return 0;
+
+	rtc_update_irq(imx_sc_rtc, 1, RTC_IRQF | RTC_AF);
+
+	return 0;
+}
+
+static struct notifier_block imx_sc_rtc_alarm_sc_notifier = {
+	.notifier_call = imx_sc_rtc_alarm_notify,
+};
+
+static int imx_sc_rtc_probe(struct platform_device *pdev)
+{
+	int ret;
+
+	ret = imx_scu_get_handle(&rtc_ipc_handle);
+	if (ret)
+		return ret;
+
+	device_init_wakeup(&pdev->dev, true);
+
+	imx_sc_rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(imx_sc_rtc))
+		return PTR_ERR(imx_sc_rtc);
+
+	imx_sc_rtc->ops = &imx_sc_rtc_ops;
+	imx_sc_rtc->range_min = 0;
+	imx_sc_rtc->range_max = U32_MAX;
+
+	ret = devm_rtc_register_device(imx_sc_rtc);
+	if (ret)
+		return ret;
+
+	imx_scu_irq_register_notifier(&imx_sc_rtc_alarm_sc_notifier);
+
+	return 0;
+}
+
+static const struct of_device_id imx_sc_dt_ids[] = {
+	{ .compatible = "fsl,imx8qxp-sc-rtc", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, imx_sc_dt_ids);
+
+static struct platform_driver imx_sc_rtc_driver = {
+	.driver = {
+		.name	= "imx-sc-rtc",
+		.of_match_table = imx_sc_dt_ids,
+	},
+	.probe		= imx_sc_rtc_probe,
+};
+module_platform_driver(imx_sc_rtc_driver);
+
+MODULE_AUTHOR("Anson Huang <Anson.Huang@nxp.com>");
+MODULE_DESCRIPTION("NXP i.MX System Controller RTC Driver");
+MODULE_LICENSE("GPL");