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, 227 insertions, 0 deletions

diff --git a/drivers/firmware/imx/sm-misc.c b/drivers/firmware/imx/sm-misc.c
new file mode 100644
index 000000000..ac9af824c
--- /dev/null
+++ b/drivers/firmware/imx/sm-misc.c
@@ -0,0 +1,227 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright 2024 NXP
+ */
+
+#include <linux/debugfs.h>
+#include <linux/device/devres.h>
+#include <linux/firmware/imx/sm.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/scmi_protocol.h>
+#include <linux/scmi_imx_protocol.h>
+#include <linux/seq_file.h>
+#include <linux/sizes.h>
+
+static const struct scmi_imx_misc_proto_ops *imx_misc_ctrl_ops;
+static struct scmi_protocol_handle *ph;
+static struct notifier_block scmi_imx_misc_ctrl_nb;
+
+static const char * const rst_imx95[] = {
+	"cm33_lockup", "cm33_swreq", "cm7_lockup", "cm7_swreq", "fccu",
+	"jtag_sw", "ele", "tempsense", "wdog1", "wdog2", "wdog3", "wdog4",
+	"wdog5", "jtag", "cm33_exc", "bbm", "sw", "sm_err", "fusa_sreco",
+	"pmic", "unused", "unused", "unused", "unused", "unused", "unused",
+	"unused", "unused", "unused", "unused", "unused", "por",
+};
+
+static const char * const rst_imx94[] = {
+	"cm33_lockup", "cm33_swreq", "cm70_lockup", "cm70_swreq", "fccu",
+	"jtag_sw", "ele", "tempsense", "wdog1", "wdog2", "wdog3", "wdog4",
+	"wdog5", "jtag", "wdog6", "wdog7", "wdog8", "wo_netc", "cm33s_lockup",
+	"cm33s_swreq", "cm71_lockup", "cm71_swreq", "cm33_exc", "bbm", "sw",
+	"sm_err", "fusa_sreco", "pmic", "unused", "unused", "unused", "por",
+};
+
+static const struct of_device_id allowlist[] = {
+	{ .compatible = "fsl,imx952", .data = rst_imx95 },
+	{ .compatible = "fsl,imx95", .data = rst_imx95 },
+	{ .compatible = "fsl,imx94", .data = rst_imx94 },
+	{ /* Sentinel */ }
+};
+
+int scmi_imx_misc_ctrl_set(u32 id, u32 val)
+{
+	if (!ph)
+		return -EPROBE_DEFER;
+
+	return imx_misc_ctrl_ops->misc_ctrl_set(ph, id, 1, &val);
+};
+EXPORT_SYMBOL(scmi_imx_misc_ctrl_set);
+
+int scmi_imx_misc_ctrl_get(u32 id, u32 *num, u32 *val)
+{
+	if (!ph)
+		return -EPROBE_DEFER;
+
+	return imx_misc_ctrl_ops->misc_ctrl_get(ph, id, num, val);
+}
+EXPORT_SYMBOL(scmi_imx_misc_ctrl_get);
+
+static int scmi_imx_misc_ctrl_notifier(struct notifier_block *nb,
+				       unsigned long event, void *data)
+{
+	/*
+	 * notifier_chain_register requires a valid notifier_block and
+	 * valid notifier_call. SCMI_EVENT_IMX_MISC_CONTROL is needed
+	 * to let SCMI firmware enable control events, but the hook here
+	 * is just a dummy function to avoid kernel panic as of now.
+	 */
+	return 0;
+}
+
+static int syslog_show(struct seq_file *file, void *priv)
+{
+	/* 4KB is large enough for syslog */
+	void *syslog __free(kfree) = kmalloc(SZ_4K, GFP_KERNEL);
+	/* syslog API use num words, not num bytes */
+	u16 size = SZ_4K / 4;
+	int ret;
+
+	if (!ph)
+		return -ENODEV;
+
+	ret = imx_misc_ctrl_ops->misc_syslog(ph, &size, syslog);
+	if (ret)
+		return ret;
+
+	seq_hex_dump(file, " ", DUMP_PREFIX_NONE, 16, sizeof(u32), syslog, size * 4, false);
+	seq_putc(file, '\n');
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(syslog);
+
+static void scmi_imx_misc_put(void *p)
+{
+	debugfs_remove((struct dentry *)p);
+}
+
+static int scmi_imx_misc_get_reason(struct scmi_device *sdev)
+{
+	struct scmi_imx_misc_reset_reason boot, shutdown;
+	const char **rst;
+	bool system = true;
+	int ret;
+
+	if (!of_machine_device_match(allowlist))
+		return 0;
+
+	rst = (const char **)of_machine_get_match_data(allowlist);
+
+	ret = imx_misc_ctrl_ops->misc_reset_reason(ph, system, &boot, &shutdown, NULL);
+	if (!ret) {
+		if (boot.valid)
+			dev_info(&sdev->dev, "%s Boot reason: %s, origin: %d, errid: %d\n",
+				 system ? "SYS" : "LM", rst[boot.reason],
+				 boot.orig_valid ? boot.origin : -1,
+				 boot.err_valid ? boot.errid : -1);
+		if (shutdown.valid)
+			dev_info(&sdev->dev, "%s shutdown reason: %s, origin: %d, errid: %d\n",
+				 system ? "SYS" : "LM", rst[shutdown.reason],
+				 shutdown.orig_valid ? shutdown.origin : -1,
+				 shutdown.err_valid ? shutdown.errid : -1);
+	} else {
+		dev_err(&sdev->dev, "Failed to get system reset reason: %d\n", ret);
+	}
+
+	system = false;
+	ret = imx_misc_ctrl_ops->misc_reset_reason(ph, system, &boot, &shutdown, NULL);
+	if (!ret) {
+		if (boot.valid)
+			dev_info(&sdev->dev, "%s Boot reason: %s, origin: %d, errid: %d\n",
+				 system ? "SYS" : "LM", rst[boot.reason],
+				 boot.orig_valid ? boot.origin : -1,
+				 boot.err_valid ? boot.errid : -1);
+		if (shutdown.valid)
+			dev_info(&sdev->dev, "%s shutdown reason: %s, origin: %d, errid: %d\n",
+				 system ? "SYS" : "LM", rst[shutdown.reason],
+				 shutdown.orig_valid ? shutdown.origin : -1,
+				 shutdown.err_valid ? shutdown.errid : -1);
+	} else {
+		dev_err(&sdev->dev, "Failed to get lm reset reason: %d\n", ret);
+	}
+
+	return 0;
+}
+
+static int scmi_imx_misc_ctrl_probe(struct scmi_device *sdev)
+{
+	const struct scmi_handle *handle = sdev->handle;
+	struct device_node *np = sdev->dev.of_node;
+	struct dentry *scmi_imx_dentry;
+	u32 src_id, flags;
+	int ret, i, num;
+
+	if (!handle)
+		return -ENODEV;
+
+	if (imx_misc_ctrl_ops) {
+		dev_err(&sdev->dev, "misc ctrl already initialized\n");
+		return -EEXIST;
+	}
+
+	imx_misc_ctrl_ops = handle->devm_protocol_get(sdev, SCMI_PROTOCOL_IMX_MISC, &ph);
+	if (IS_ERR(imx_misc_ctrl_ops))
+		return PTR_ERR(imx_misc_ctrl_ops);
+
+	num = of_property_count_u32_elems(np, "nxp,ctrl-ids");
+	if (num % 2) {
+		dev_err(&sdev->dev, "Invalid wakeup-sources\n");
+		return -EINVAL;
+	}
+
+	scmi_imx_misc_ctrl_nb.notifier_call = &scmi_imx_misc_ctrl_notifier;
+	for (i = 0; i < num; i += 2) {
+		ret = of_property_read_u32_index(np, "nxp,ctrl-ids", i, &src_id);
+		if (ret) {
+			dev_err(&sdev->dev, "Failed to read ctrl-id: %i\n", i);
+			continue;
+		}
+
+		ret = of_property_read_u32_index(np, "nxp,ctrl-ids", i + 1, &flags);
+		if (ret) {
+			dev_err(&sdev->dev, "Failed to read ctrl-id value: %d\n", i + 1);
+			continue;
+		}
+
+		ret = handle->notify_ops->devm_event_notifier_register(sdev, SCMI_PROTOCOL_IMX_MISC,
+								       SCMI_EVENT_IMX_MISC_CONTROL,
+								       &src_id,
+								       &scmi_imx_misc_ctrl_nb);
+		if (ret) {
+			dev_err(&sdev->dev, "Failed to register scmi misc event: %d\n", src_id);
+		} else {
+			ret = imx_misc_ctrl_ops->misc_ctrl_req_notify(ph, src_id,
+								      SCMI_EVENT_IMX_MISC_CONTROL,
+								      flags);
+			if (ret)
+				dev_err(&sdev->dev, "Failed to req notify: %d\n", src_id);
+		}
+	}
+
+	scmi_imx_dentry = debugfs_create_dir("scmi_imx", NULL);
+	debugfs_create_file("syslog", 0444, scmi_imx_dentry, &sdev->dev, &syslog_fops);
+
+	scmi_imx_misc_get_reason(sdev);
+
+	return devm_add_action_or_reset(&sdev->dev, scmi_imx_misc_put, scmi_imx_dentry);
+}
+
+static const struct scmi_device_id scmi_id_table[] = {
+	{ SCMI_PROTOCOL_IMX_MISC, "imx-misc-ctrl" },
+	{ },
+};
+MODULE_DEVICE_TABLE(scmi, scmi_id_table);
+
+static struct scmi_driver scmi_imx_misc_ctrl_driver = {
+	.name = "scmi-imx-misc-ctrl",
+	.probe = scmi_imx_misc_ctrl_probe,
+	.id_table = scmi_id_table,
+};
+module_scmi_driver(scmi_imx_misc_ctrl_driver);
+
+MODULE_AUTHOR("Peng Fan <peng.fan@nxp.com>");
+MODULE_DESCRIPTION("IMX SM MISC driver");
+MODULE_LICENSE("GPL");