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, 535 insertions, 0 deletions

diff --git a/drivers/char/dsp56k.c b/drivers/char/dsp56k.c
new file mode 100644
index 000000000..1c2c84397
--- /dev/null
+++ b/drivers/char/dsp56k.c
@@ -0,0 +1,535 @@
+/*
+ * The DSP56001 Device Driver, saviour of the Free World(tm)
+ *
+ * Authors: Fredrik Noring   <noring@nocrew.org>
+ *          lars brinkhoff   <lars@nocrew.org>
+ *          Tomas Berndtsson <tomas@nocrew.org>
+ *
+ * First version May 1996
+ *
+ * History:
+ *  97-01-29   Tomas Berndtsson,
+ *               Integrated with Linux 2.1.21 kernel sources.
+ *  97-02-15   Tomas Berndtsson,
+ *               Fixed for kernel 2.1.26
+ *
+ * BUGS:
+ *  Hmm... there must be something here :)
+ *
+ * Copyright (C) 1996,1997 Fredrik Noring, lars brinkhoff & Tomas Berndtsson
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file COPYING in the main directory of this archive
+ * for more details.
+ */
+
+#include <linux/module.h>
+#include <linux/major.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/delay.h>	/* guess what */
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/init.h>
+#include <linux/device.h>
+#include <linux/mutex.h>
+#include <linux/firmware.h>
+#include <linux/platform_device.h>
+#include <linux/uaccess.h>	/* For put_user and get_user */
+
+#include <asm/atarihw.h>
+#include <asm/traps.h>
+
+#include <asm/dsp56k.h>
+
+/* minor devices */
+#define DSP56K_DEV_56001        0    /* The only device so far */
+
+#define TIMEOUT    10   /* Host port timeout in number of tries */
+#define MAXIO    2048   /* Maximum number of words before sleep */
+#define DSP56K_MAX_BINARY_LENGTH (3*64*1024)
+
+#define DSP56K_TX_INT_ON	dsp56k_host_interface.icr |=  DSP56K_ICR_TREQ
+#define DSP56K_RX_INT_ON	dsp56k_host_interface.icr |=  DSP56K_ICR_RREQ
+#define DSP56K_TX_INT_OFF	dsp56k_host_interface.icr &= ~DSP56K_ICR_TREQ
+#define DSP56K_RX_INT_OFF	dsp56k_host_interface.icr &= ~DSP56K_ICR_RREQ
+
+#define DSP56K_TRANSMIT		(dsp56k_host_interface.isr & DSP56K_ISR_TXDE)
+#define DSP56K_RECEIVE		(dsp56k_host_interface.isr & DSP56K_ISR_RXDF)
+
+#define handshake(count, maxio, timeout, ENABLE, f) \
+{ \
+	long i, t, m; \
+	while (count > 0) { \
+		m = min_t(unsigned long, count, maxio); \
+		for (i = 0; i < m; i++) { \
+			for (t = 0; t < timeout && !ENABLE; t++) \
+				msleep(20); \
+			if(!ENABLE) \
+				return -EIO; \
+			f; \
+		} \
+		count -= m; \
+		if (m == maxio) msleep(20); \
+	} \
+}
+
+#define tx_wait(n) \
+{ \
+	int t; \
+	for(t = 0; t < n && !DSP56K_TRANSMIT; t++) \
+		msleep(10); \
+	if(!DSP56K_TRANSMIT) { \
+		return -EIO; \
+	} \
+}
+
+#define rx_wait(n) \
+{ \
+	int t; \
+	for(t = 0; t < n && !DSP56K_RECEIVE; t++) \
+		msleep(10); \
+	if(!DSP56K_RECEIVE) { \
+		return -EIO; \
+	} \
+}
+
+static DEFINE_MUTEX(dsp56k_mutex);
+static struct dsp56k_device {
+	unsigned long in_use;
+	long maxio, timeout;
+	int tx_wsize, rx_wsize;
+} dsp56k;
+
+static const struct class dsp56k_class = {
+	.name = "dsp56k",
+};
+
+static int dsp56k_reset(void)
+{
+	u_char status;
+	
+	/* Power down the DSP */
+	sound_ym.rd_data_reg_sel = 14;
+	status = sound_ym.rd_data_reg_sel & 0xef;
+	sound_ym.wd_data = status;
+	sound_ym.wd_data = status | 0x10;
+  
+	udelay(10);
+  
+	/* Power up the DSP */
+	sound_ym.rd_data_reg_sel = 14;
+	sound_ym.wd_data = sound_ym.rd_data_reg_sel & 0xef;
+
+	return 0;
+}
+
+static int dsp56k_upload(u_char __user *bin, int len)
+{
+	struct platform_device *pdev;
+	const struct firmware *fw;
+	const char fw_name[] = "dsp56k/bootstrap.bin";
+	int err;
+	int i;
+
+	dsp56k_reset();
+
+	pdev = platform_device_register_simple("dsp56k", 0, NULL, 0);
+	if (IS_ERR(pdev)) {
+		printk(KERN_ERR "Failed to register device for \"%s\"\n",
+		       fw_name);
+		return -EINVAL;
+	}
+	err = request_firmware(&fw, fw_name, &pdev->dev);
+	platform_device_unregister(pdev);
+	if (err) {
+		printk(KERN_ERR "Failed to load image \"%s\" err %d\n",
+		       fw_name, err);
+		return err;
+	}
+	if (fw->size % 3) {
+		printk(KERN_ERR "Bogus length %d in image \"%s\"\n",
+		       fw->size, fw_name);
+		release_firmware(fw);
+		return -EINVAL;
+	}
+	for (i = 0; i < fw->size; i = i + 3) {
+		/* tx_wait(10); */
+		dsp56k_host_interface.data.b[1] = fw->data[i];
+		dsp56k_host_interface.data.b[2] = fw->data[i + 1];
+		dsp56k_host_interface.data.b[3] = fw->data[i + 2];
+	}
+	release_firmware(fw);
+	for (; i < 512; i++) {
+		/* tx_wait(10); */
+		dsp56k_host_interface.data.b[1] = 0;
+		dsp56k_host_interface.data.b[2] = 0;
+		dsp56k_host_interface.data.b[3] = 0;
+	}
+  
+	for (i = 0; i < len; i++) {
+		tx_wait(10);
+		get_user(dsp56k_host_interface.data.b[1], bin++);
+		get_user(dsp56k_host_interface.data.b[2], bin++);
+		get_user(dsp56k_host_interface.data.b[3], bin++);
+	}
+
+	tx_wait(10);
+	dsp56k_host_interface.data.l = 3;    /* Magic execute */
+
+	return 0;
+}
+
+static ssize_t dsp56k_read(struct file *file, char __user *buf, size_t count,
+			   loff_t *ppos)
+{
+	struct inode *inode = file_inode(file);
+	int dev = iminor(inode) & 0x0f;
+
+	switch(dev)
+	{
+	case DSP56K_DEV_56001:
+	{
+
+		long n;
+
+		/* Don't do anything if nothing is to be done */
+		if (!count) return 0;
+
+		n = 0;
+		switch (dsp56k.rx_wsize) {
+		case 1:  /* 8 bit */
+		{
+			handshake(count, dsp56k.maxio, dsp56k.timeout, DSP56K_RECEIVE,
+				  put_user(dsp56k_host_interface.data.b[3], buf+n++));
+			return n;
+		}
+		case 2:  /* 16 bit */
+		{
+			short __user *data;
+
+			count /= 2;
+			data = (short __user *) buf;
+			handshake(count, dsp56k.maxio, dsp56k.timeout, DSP56K_RECEIVE,
+				  put_user(dsp56k_host_interface.data.w[1], data+n++));
+			return 2*n;
+		}
+		case 3:  /* 24 bit */
+		{
+			count /= 3;
+			handshake(count, dsp56k.maxio, dsp56k.timeout, DSP56K_RECEIVE,
+				  put_user(dsp56k_host_interface.data.b[1], buf+n++);
+				  put_user(dsp56k_host_interface.data.b[2], buf+n++);
+				  put_user(dsp56k_host_interface.data.b[3], buf+n++));
+			return 3*n;
+		}
+		case 4:  /* 32 bit */
+		{
+			long __user *data;
+
+			count /= 4;
+			data = (long __user *) buf;
+			handshake(count, dsp56k.maxio, dsp56k.timeout, DSP56K_RECEIVE,
+				  put_user(dsp56k_host_interface.data.l, data+n++));
+			return 4*n;
+		}
+		}
+		return -EFAULT;
+	}
+
+	default:
+		printk(KERN_ERR "DSP56k driver: Unknown minor device: %d\n", dev);
+		return -ENXIO;
+	}
+}
+
+static ssize_t dsp56k_write(struct file *file, const char __user *buf, size_t count,
+			    loff_t *ppos)
+{
+	struct inode *inode = file_inode(file);
+	int dev = iminor(inode) & 0x0f;
+
+	switch(dev)
+	{
+	case DSP56K_DEV_56001:
+	{
+		long n;
+
+		/* Don't do anything if nothing is to be done */
+		if (!count) return 0;
+
+		n = 0;
+		switch (dsp56k.tx_wsize) {
+		case 1:  /* 8 bit */
+		{
+			handshake(count, dsp56k.maxio, dsp56k.timeout, DSP56K_TRANSMIT,
+				  get_user(dsp56k_host_interface.data.b[3], buf+n++));
+			return n;
+		}
+		case 2:  /* 16 bit */
+		{
+			const short __user *data;
+
+			count /= 2;
+			data = (const short __user *)buf;
+			handshake(count, dsp56k.maxio, dsp56k.timeout, DSP56K_TRANSMIT,
+				  get_user(dsp56k_host_interface.data.w[1], data+n++));
+			return 2*n;
+		}
+		case 3:  /* 24 bit */
+		{
+			count /= 3;
+			handshake(count, dsp56k.maxio, dsp56k.timeout, DSP56K_TRANSMIT,
+				  get_user(dsp56k_host_interface.data.b[1], buf+n++);
+				  get_user(dsp56k_host_interface.data.b[2], buf+n++);
+				  get_user(dsp56k_host_interface.data.b[3], buf+n++));
+			return 3*n;
+		}
+		case 4:  /* 32 bit */
+		{
+			const long __user *data;
+
+			count /= 4;
+			data = (const long __user *)buf;
+			handshake(count, dsp56k.maxio, dsp56k.timeout, DSP56K_TRANSMIT,
+				  get_user(dsp56k_host_interface.data.l, data+n++));
+			return 4*n;
+		}
+		}
+
+		return -EFAULT;
+	}
+	default:
+		printk(KERN_ERR "DSP56k driver: Unknown minor device: %d\n", dev);
+		return -ENXIO;
+	}
+}
+
+static long dsp56k_ioctl(struct file *file, unsigned int cmd,
+			 unsigned long arg)
+{
+	int dev = iminor(file_inode(file)) & 0x0f;
+	void __user *argp = (void __user *)arg;
+
+	switch(dev)
+	{
+	case DSP56K_DEV_56001:
+
+		switch(cmd) {
+		case DSP56K_UPLOAD:
+		{
+			char __user *bin;
+			int r, len;
+			struct dsp56k_upload __user *binary = argp;
+    
+			if(get_user(len, &binary->len) < 0)
+				return -EFAULT;
+			if(get_user(bin, &binary->bin) < 0)
+				return -EFAULT;
+		
+			if (len <= 0) {
+				return -EINVAL;      /* nothing to upload?!? */
+			}
+			if (len > DSP56K_MAX_BINARY_LENGTH) {
+				return -EINVAL;
+			}
+			mutex_lock(&dsp56k_mutex);
+			r = dsp56k_upload(bin, len);
+			mutex_unlock(&dsp56k_mutex);
+			if (r < 0) {
+				return r;
+			}
+    
+			break;
+		}
+		case DSP56K_SET_TX_WSIZE:
+			if (arg > 4 || arg < 1)
+				return -EINVAL;
+			mutex_lock(&dsp56k_mutex);
+			dsp56k.tx_wsize = (int) arg;
+			mutex_unlock(&dsp56k_mutex);
+			break;
+		case DSP56K_SET_RX_WSIZE:
+			if (arg > 4 || arg < 1)
+				return -EINVAL;
+			mutex_lock(&dsp56k_mutex);
+			dsp56k.rx_wsize = (int) arg;
+			mutex_unlock(&dsp56k_mutex);
+			break;
+		case DSP56K_HOST_FLAGS:
+		{
+			int dir, out, status;
+			struct dsp56k_host_flags __user *hf = argp;
+    
+			if(get_user(dir, &hf->dir) < 0)
+				return -EFAULT;
+			if(get_user(out, &hf->out) < 0)
+				return -EFAULT;
+
+			mutex_lock(&dsp56k_mutex);
+			if ((dir & 0x1) && (out & 0x1))
+				dsp56k_host_interface.icr |= DSP56K_ICR_HF0;
+			else if (dir & 0x1)
+				dsp56k_host_interface.icr &= ~DSP56K_ICR_HF0;
+			if ((dir & 0x2) && (out & 0x2))
+				dsp56k_host_interface.icr |= DSP56K_ICR_HF1;
+			else if (dir & 0x2)
+				dsp56k_host_interface.icr &= ~DSP56K_ICR_HF1;
+
+			status = 0;
+			if (dsp56k_host_interface.icr & DSP56K_ICR_HF0) status |= 0x1;
+			if (dsp56k_host_interface.icr & DSP56K_ICR_HF1) status |= 0x2;
+			if (dsp56k_host_interface.isr & DSP56K_ISR_HF2) status |= 0x4;
+			if (dsp56k_host_interface.isr & DSP56K_ISR_HF3) status |= 0x8;
+			mutex_unlock(&dsp56k_mutex);
+			return put_user(status, &hf->status);
+		}
+		case DSP56K_HOST_CMD:
+			if (arg > 31)
+				return -EINVAL;
+			mutex_lock(&dsp56k_mutex);
+			dsp56k_host_interface.cvr = (u_char)((arg & DSP56K_CVR_HV_MASK) |
+							     DSP56K_CVR_HC);
+			mutex_unlock(&dsp56k_mutex);
+			break;
+		default:
+			return -EINVAL;
+		}
+		return 0;
+
+	default:
+		printk(KERN_ERR "DSP56k driver: Unknown minor device: %d\n", dev);
+		return -ENXIO;
+	}
+}
+
+/* As of 2.1.26 this should be dsp56k_poll,
+ * but how do I then check device minor number?
+ * Do I need this function at all???
+ */
+#if 0
+static __poll_t dsp56k_poll(struct file *file, poll_table *wait)
+{
+	int dev = iminor(file_inode(file)) & 0x0f;
+
+	switch(dev)
+	{
+	case DSP56K_DEV_56001:
+		/* poll_wait(file, ???, wait); */
+		return EPOLLIN | EPOLLRDNORM | EPOLLOUT;
+
+	default:
+		printk("DSP56k driver: Unknown minor device: %d\n", dev);
+		return 0;
+	}
+}
+#endif
+
+static int dsp56k_open(struct inode *inode, struct file *file)
+{
+	int dev = iminor(inode) & 0x0f;
+	int ret = 0;
+
+	mutex_lock(&dsp56k_mutex);
+	switch(dev)
+	{
+	case DSP56K_DEV_56001:
+
+		if (test_and_set_bit(0, &dsp56k.in_use)) {
+			ret = -EBUSY;
+			goto out;
+		}
+
+		dsp56k.timeout = TIMEOUT;
+		dsp56k.maxio = MAXIO;
+		dsp56k.rx_wsize = dsp56k.tx_wsize = 4; 
+
+		DSP56K_TX_INT_OFF;
+		DSP56K_RX_INT_OFF;
+
+		/* Zero host flags */
+		dsp56k_host_interface.icr &= ~DSP56K_ICR_HF0;
+		dsp56k_host_interface.icr &= ~DSP56K_ICR_HF1;
+
+		break;
+
+	default:
+		ret = -ENODEV;
+	}
+out:
+	mutex_unlock(&dsp56k_mutex);
+	return ret;
+}
+
+static int dsp56k_release(struct inode *inode, struct file *file)
+{
+	int dev = iminor(inode) & 0x0f;
+
+	switch(dev)
+	{
+	case DSP56K_DEV_56001:
+		clear_bit(0, &dsp56k.in_use);
+		break;
+	default:
+		printk(KERN_ERR "DSP56k driver: Unknown minor device: %d\n", dev);
+		return -ENXIO;
+	}
+
+	return 0;
+}
+
+static const struct file_operations dsp56k_fops = {
+	.owner		= THIS_MODULE,
+	.read		= dsp56k_read,
+	.write		= dsp56k_write,
+	.unlocked_ioctl	= dsp56k_ioctl,
+	.open		= dsp56k_open,
+	.release	= dsp56k_release,
+	.llseek		= noop_llseek,
+};
+
+
+/****** Init and module functions ******/
+
+static const char banner[] __initconst = KERN_INFO "DSP56k driver installed\n";
+
+static int __init dsp56k_init_driver(void)
+{
+	int err;
+
+	if(!MACH_IS_ATARI || !ATARIHW_PRESENT(DSP56K)) {
+		printk("DSP56k driver: Hardware not present\n");
+		return -ENODEV;
+	}
+
+	if(register_chrdev(DSP56K_MAJOR, "dsp56k", &dsp56k_fops)) {
+		printk("DSP56k driver: Unable to register driver\n");
+		return -ENODEV;
+	}
+	err = class_register(&dsp56k_class);
+	if (err)
+		goto out_chrdev;
+	device_create(&dsp56k_class, NULL, MKDEV(DSP56K_MAJOR, 0), NULL,
+		      "dsp56k");
+
+	printk(banner);
+	goto out;
+
+out_chrdev:
+	unregister_chrdev(DSP56K_MAJOR, "dsp56k");
+out:
+	return err;
+}
+module_init(dsp56k_init_driver);
+
+static void __exit dsp56k_cleanup_driver(void)
+{
+	device_destroy(&dsp56k_class, MKDEV(DSP56K_MAJOR, 0));
+	class_unregister(&dsp56k_class);
+	unregister_chrdev(DSP56K_MAJOR, "dsp56k");
+}
+module_exit(dsp56k_cleanup_driver);
+
+MODULE_DESCRIPTION("Atari DSP56001 Device Driver");
+MODULE_LICENSE("GPL");
+MODULE_FIRMWARE("dsp56k/bootstrap.bin");