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, 130 insertions, 0 deletions

diff --git a/drivers/leds/leds-wrap.c b/drivers/leds/leds-wrap.c
new file mode 100644
index 000000000..794697e16
--- /dev/null
+++ b/drivers/leds/leds-wrap.c
@@ -0,0 +1,130 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * LEDs driver for PCEngines WRAP
+ *
+ * Copyright (C) 2006 Kristian Kielhofner <kris@krisk.org>
+ *
+ * Based on leds-net48xx.c
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/platform_device.h>
+#include <linux/leds.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/scx200_gpio.h>
+#include <linux/module.h>
+
+#define DRVNAME "wrap-led"
+#define WRAP_POWER_LED_GPIO	2
+#define WRAP_ERROR_LED_GPIO	3
+#define WRAP_EXTRA_LED_GPIO	18
+
+static struct platform_device *pdev;
+
+static void wrap_power_led_set(struct led_classdev *led_cdev,
+		enum led_brightness value)
+{
+	if (value)
+		scx200_gpio_set_low(WRAP_POWER_LED_GPIO);
+	else
+		scx200_gpio_set_high(WRAP_POWER_LED_GPIO);
+}
+
+static void wrap_error_led_set(struct led_classdev *led_cdev,
+		enum led_brightness value)
+{
+	if (value)
+		scx200_gpio_set_low(WRAP_ERROR_LED_GPIO);
+	else
+		scx200_gpio_set_high(WRAP_ERROR_LED_GPIO);
+}
+
+static void wrap_extra_led_set(struct led_classdev *led_cdev,
+		enum led_brightness value)
+{
+	if (value)
+		scx200_gpio_set_low(WRAP_EXTRA_LED_GPIO);
+	else
+		scx200_gpio_set_high(WRAP_EXTRA_LED_GPIO);
+}
+
+static struct led_classdev wrap_power_led = {
+	.name			= "wrap::power",
+	.brightness_set		= wrap_power_led_set,
+	.default_trigger	= "default-on",
+	.flags			= LED_CORE_SUSPENDRESUME,
+};
+
+static struct led_classdev wrap_error_led = {
+	.name		= "wrap::error",
+	.brightness_set	= wrap_error_led_set,
+	.flags			= LED_CORE_SUSPENDRESUME,
+};
+
+static struct led_classdev wrap_extra_led = {
+	.name           = "wrap::extra",
+	.brightness_set = wrap_extra_led_set,
+	.flags			= LED_CORE_SUSPENDRESUME,
+};
+
+static int wrap_led_probe(struct platform_device *pdev)
+{
+	int ret;
+
+	ret = devm_led_classdev_register(&pdev->dev, &wrap_power_led);
+	if (ret < 0)
+		return ret;
+
+	ret = devm_led_classdev_register(&pdev->dev, &wrap_error_led);
+	if (ret < 0)
+		return ret;
+
+	return  devm_led_classdev_register(&pdev->dev, &wrap_extra_led);
+}
+
+static struct platform_driver wrap_led_driver = {
+	.probe		= wrap_led_probe,
+	.driver		= {
+		.name		= DRVNAME,
+	},
+};
+
+static int __init wrap_led_init(void)
+{
+	int ret;
+
+	if (!scx200_gpio_present()) {
+		ret = -ENODEV;
+		goto out;
+	}
+
+	ret = platform_driver_register(&wrap_led_driver);
+	if (ret < 0)
+		goto out;
+
+	pdev = platform_device_register_simple(DRVNAME, -1, NULL, 0);
+	if (IS_ERR(pdev)) {
+		ret = PTR_ERR(pdev);
+		platform_driver_unregister(&wrap_led_driver);
+		goto out;
+	}
+
+out:
+	return ret;
+}
+
+static void __exit wrap_led_exit(void)
+{
+	platform_device_unregister(pdev);
+	platform_driver_unregister(&wrap_led_driver);
+}
+
+module_init(wrap_led_init);
+module_exit(wrap_led_exit);
+
+MODULE_AUTHOR("Kristian Kielhofner <kris@krisk.org>");
+MODULE_DESCRIPTION("PCEngines WRAP LED driver");
+MODULE_LICENSE("GPL");
+