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, 266 insertions, 0 deletions

diff --git a/drivers/parisc/power.c b/drivers/parisc/power.c
new file mode 100644
index 000000000..9d6c7bf72
--- /dev/null
+++ b/drivers/parisc/power.c
@@ -0,0 +1,266 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * HP PARISC soft power switch driver
+ *
+ * Copyright (c) 2001-2023 Helge Deller <deller@gmx.de>
+ *
+ *  HINT:
+ *  Support of the soft power switch button may be enabled or disabled at
+ *  runtime through the "/proc/sys/kernel/power" procfs entry.
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/panic_notifier.h>
+#include <linux/reboot.h>
+#include <linux/sched/signal.h>
+#include <linux/kthread.h>
+#include <linux/pm.h>
+
+#include <asm/pdc.h>
+#include <asm/io.h>
+#include <asm/led.h>
+
+#define DRIVER_NAME  "powersw"
+#define KTHREAD_NAME "kpowerswd"
+
+/* how often should the power button be polled ? */
+#define POWERSWITCH_POLL_PER_SEC 2
+
+/* how long does the power button needs to be down until we react ? */
+#define POWERSWITCH_DOWN_SEC 2
+
+/* assembly code to access special registers */
+/* taken from PCXL ERS page 82 */
+#define DIAG_CODE(code)		(0x14000000 + ((code)<<5))
+
+#define MFCPU_X(rDiagReg, t_ch, t_th, code) \
+	(DIAG_CODE(code) + ((rDiagReg)<<21) + ((t_ch)<<16) + ((t_th)<<0) )
+
+#define MTCPU(dr, gr)		MFCPU_X(dr, gr,  0, 0x12)       /* move value of gr to dr[dr] */
+#define MFCPU_C(dr, gr)		MFCPU_X(dr, gr,  0, 0x30)	/* for dr0 and dr8 only ! */
+#define MFCPU_T(dr, gr)		MFCPU_X(dr,  0, gr, 0xa0)	/* all dr except dr0 and dr8 */
+
+#define __getDIAG(dr) ( {			\
+        register unsigned long __res asm("r28");\
+	 __asm__ __volatile__ (			\
+		".word %1" : "=&r" (__res) : "i" (MFCPU_T(dr,28) ) \
+	);					\
+	__res;					\
+} )
+
+/* local shutdown counter */
+static int shutdown_timer __read_mostly;
+
+/* check, give feedback and start shutdown after one second */
+static void process_shutdown(void)
+{
+	if (shutdown_timer == 0)
+		printk(KERN_ALERT KTHREAD_NAME ": Shutdown requested...\n");
+
+	shutdown_timer++;
+
+	/* wait until the button was pressed for 1 second */
+	if (shutdown_timer == (POWERSWITCH_DOWN_SEC*POWERSWITCH_POLL_PER_SEC)) {
+		static const char msg[] = "Shutting down...";
+		printk(KERN_INFO KTHREAD_NAME ": %s\n", msg);
+		lcd_print(msg);
+
+		/* send kill signal */
+		if (kill_cad_pid(SIGINT, 1)) {
+			/* just in case killing init process failed */
+			machine_power_off();
+		}
+	}
+}
+
+
+/* main power switch task struct */
+static struct task_struct *power_task;
+
+/* filename in /proc which can be used to enable/disable the power switch */
+#define SYSCTL_FILENAME	"sys/kernel/power"
+
+/* soft power switch enabled/disabled */
+static int pwrsw_enabled __read_mostly = 1;
+
+static const struct ctl_table power_sysctl_table[] = {
+	{
+		.procname	= "soft-power",
+		.data		= &pwrsw_enabled,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec,
+	},
+};
+
+static int __init init_power_sysctl(void)
+{
+	register_sysctl_init("kernel", power_sysctl_table);
+	return 0;
+}
+
+arch_initcall(init_power_sysctl);
+
+/* main kernel thread worker. It polls the button state */
+static int kpowerswd(void *param)
+{
+	__set_current_state(TASK_RUNNING);
+
+	do {
+		int button_not_pressed;
+		unsigned long soft_power_reg = (unsigned long) param;
+
+		schedule_timeout_interruptible(pwrsw_enabled ? HZ : HZ/POWERSWITCH_POLL_PER_SEC);
+
+		if (unlikely(!pwrsw_enabled))
+			continue;
+
+		if (soft_power_reg) {
+			/*
+			 * Non-Gecko-style machines:
+			 * Check the power switch status which is read from the
+			 * real I/O location at soft_power_reg.
+			 * Bit 31 ("the lowest bit) is the status of the power switch.
+			 * This bit is "1" if the button is NOT pressed.
+			 */
+			button_not_pressed = (gsc_readl(soft_power_reg) & 0x1);
+		} else {
+			/*
+			 * On gecko style machines (e.g. 712/xx and 715/xx)
+			 * the power switch status is stored in Bit 0 ("the highest bit")
+			 * of CPU diagnose register 25.
+			 * Warning: Some machines never reset the DIAG flag, even if
+			 * the button has been released again.
+			 */
+			button_not_pressed = (__getDIAG(25) & 0x80000000);
+		}
+
+		if (likely(button_not_pressed)) {
+			if (unlikely(shutdown_timer && /* avoid writing if not necessary */
+				shutdown_timer < (POWERSWITCH_DOWN_SEC*POWERSWITCH_POLL_PER_SEC))) {
+				shutdown_timer = 0;
+				printk(KERN_INFO KTHREAD_NAME ": Shutdown request aborted.\n");
+			}
+		} else
+			process_shutdown();
+
+
+	} while (!kthread_should_stop());
+
+	return 0;
+}
+
+
+/*
+ * powerfail interruption handler (irq IRQ_FROM_REGION(CPU_IRQ_REGION)+2)
+ */
+#if 0
+static void powerfail_interrupt(int code, void *x)
+{
+	printk(KERN_CRIT "POWERFAIL INTERRUPTION !\n");
+	poweroff();
+}
+#endif
+
+
+
+
+/*
+ * parisc_panic_event() is called by the panic handler.
+ *
+ * As soon as a panic occurs, our tasklets above will not
+ * be executed any longer. This function then re-enables
+ * the soft-power switch and allows the user to switch off
+ * the system. We rely in pdc_soft_power_button_panic()
+ * since this version spin_trylocks (instead of regular
+ * spinlock), preventing deadlocks on panic path.
+ */
+static int parisc_panic_event(struct notifier_block *this,
+		unsigned long event, void *ptr)
+{
+	/* re-enable the soft-power switch */
+	pdc_soft_power_button_panic(0);
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block parisc_panic_block = {
+	.notifier_call	= parisc_panic_event,
+	.priority	= INT_MAX,
+};
+
+/* qemu soft power-off function */
+static int qemu_power_off(struct sys_off_data *data)
+{
+	/* this turns the system off via SeaBIOS */
+	gsc_writel(0, (unsigned long) data->cb_data);
+	pdc_soft_power_button(1);
+	return NOTIFY_DONE;
+}
+
+static int __init power_init(void)
+{
+	unsigned long ret;
+	unsigned long soft_power_reg;
+
+#if 0
+	request_irq( IRQ_FROM_REGION(CPU_IRQ_REGION)+2, &powerfail_interrupt,
+		0, "powerfail", NULL);
+#endif
+
+	/* enable the soft power switch if possible */
+	ret = pdc_soft_power_info(&soft_power_reg);
+	if (ret == PDC_OK)
+		ret = pdc_soft_power_button(1);
+	if (ret != PDC_OK)
+		soft_power_reg = -1UL;
+
+	switch (soft_power_reg) {
+	case 0:		printk(KERN_INFO DRIVER_NAME ": Gecko-style soft power switch enabled.\n");
+			break;
+
+	case -1UL:	printk(KERN_INFO DRIVER_NAME ": Soft power switch support not available.\n");
+			return -ENODEV;
+
+	default:	printk(KERN_INFO DRIVER_NAME ": Soft power switch at 0x%08lx enabled.\n",
+				soft_power_reg);
+	}
+
+	power_task = NULL;
+	if (running_on_qemu && soft_power_reg)
+		register_sys_off_handler(SYS_OFF_MODE_POWER_OFF, SYS_OFF_PRIO_DEFAULT,
+					qemu_power_off, (void *)soft_power_reg);
+	if (!running_on_qemu || soft_power_reg)
+		power_task = kthread_run(kpowerswd, (void*)soft_power_reg,
+					KTHREAD_NAME);
+	if (IS_ERR(power_task)) {
+		printk(KERN_ERR DRIVER_NAME ": thread creation failed.  Driver not loaded.\n");
+		pdc_soft_power_button(0);
+		return -EIO;
+	}
+
+	/* Register a call for panic conditions. */
+	atomic_notifier_chain_register(&panic_notifier_list,
+			&parisc_panic_block);
+
+	return 0;
+}
+
+static void __exit power_exit(void)
+{
+	kthread_stop(power_task);
+
+	atomic_notifier_chain_unregister(&panic_notifier_list,
+			&parisc_panic_block);
+
+	pdc_soft_power_button(0);
+}
+
+arch_initcall(power_init);
+module_exit(power_exit);
+
+
+MODULE_AUTHOR("Helge Deller <deller@gmx.de>");
+MODULE_DESCRIPTION("Soft power switch driver");
+MODULE_LICENSE("Dual BSD/GPL");