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, 445 insertions, 0 deletions

diff --git a/drivers/char/ps3flash.c b/drivers/char/ps3flash.c
new file mode 100644
index 000000000..c73f44307
--- /dev/null
+++ b/drivers/char/ps3flash.c
@@ -0,0 +1,445 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * PS3 FLASH ROM Storage Driver
+ *
+ * Copyright (C) 2007 Sony Computer Entertainment Inc.
+ * Copyright 2007 Sony Corp.
+ */
+
+#include <linux/fs.h>
+#include <linux/miscdevice.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <linux/module.h>
+
+#include <asm/lv1call.h>
+#include <asm/ps3stor.h>
+
+
+#define DEVICE_NAME		"ps3flash"
+
+#define FLASH_BLOCK_SIZE	(256*1024)
+
+
+struct ps3flash_private {
+	struct mutex mutex;	/* Bounce buffer mutex */
+	u64 chunk_sectors;
+	int tag;		/* Start sector of buffer, -1 if invalid */
+	bool dirty;
+};
+
+static struct ps3_storage_device *ps3flash_dev;
+
+static int ps3flash_read_write_sectors(struct ps3_storage_device *dev,
+				       u64 start_sector, int write)
+{
+	struct ps3flash_private *priv = ps3_system_bus_get_drvdata(&dev->sbd);
+	u64 res = ps3stor_read_write_sectors(dev, dev->bounce_lpar,
+					     start_sector, priv->chunk_sectors,
+					     write);
+	if (res) {
+		dev_err(&dev->sbd.core, "%s:%u: %s failed 0x%llx\n", __func__,
+			__LINE__, write ? "write" : "read", res);
+		return -EIO;
+	}
+	return 0;
+}
+
+static int ps3flash_writeback(struct ps3_storage_device *dev)
+{
+	struct ps3flash_private *priv = ps3_system_bus_get_drvdata(&dev->sbd);
+	int res;
+
+	if (!priv->dirty || priv->tag < 0)
+		return 0;
+
+	res = ps3flash_read_write_sectors(dev, priv->tag, 1);
+	if (res)
+		return res;
+
+	priv->dirty = false;
+	return 0;
+}
+
+static int ps3flash_fetch(struct ps3_storage_device *dev, u64 start_sector)
+{
+	struct ps3flash_private *priv = ps3_system_bus_get_drvdata(&dev->sbd);
+	int res;
+
+	if (start_sector == priv->tag)
+		return 0;
+
+	res = ps3flash_writeback(dev);
+	if (res)
+		return res;
+
+	priv->tag = -1;
+
+	res = ps3flash_read_write_sectors(dev, start_sector, 0);
+	if (res)
+		return res;
+
+	priv->tag = start_sector;
+	return 0;
+}
+
+static loff_t ps3flash_llseek(struct file *file, loff_t offset, int origin)
+{
+	struct ps3_storage_device *dev = ps3flash_dev;
+	return generic_file_llseek_size(file, offset, origin, MAX_LFS_FILESIZE,
+			dev->regions[dev->region_idx].size*dev->blk_size);
+}
+
+static ssize_t ps3flash_read(char __user *userbuf, void *kernelbuf,
+			     size_t count, loff_t *pos)
+{
+	struct ps3_storage_device *dev = ps3flash_dev;
+	struct ps3flash_private *priv = ps3_system_bus_get_drvdata(&dev->sbd);
+	u64 size, sector, offset;
+	int res;
+	size_t remaining, n;
+	const void *src;
+
+	dev_dbg(&dev->sbd.core,
+		"%s:%u: Reading %zu bytes at position %lld to U0x%p/K0x%p\n",
+		__func__, __LINE__, count, *pos, userbuf, kernelbuf);
+
+	size = dev->regions[dev->region_idx].size*dev->blk_size;
+	if (*pos >= size || !count)
+		return 0;
+
+	if (*pos + count > size) {
+		dev_dbg(&dev->sbd.core,
+			"%s:%u Truncating count from %zu to %llu\n", __func__,
+			__LINE__, count, size - *pos);
+		count = size - *pos;
+	}
+
+	sector = *pos / dev->bounce_size * priv->chunk_sectors;
+	offset = *pos % dev->bounce_size;
+
+	remaining = count;
+	do {
+		n = min_t(u64, remaining, dev->bounce_size - offset);
+		src = dev->bounce_buf + offset;
+
+		mutex_lock(&priv->mutex);
+
+		res = ps3flash_fetch(dev, sector);
+		if (res)
+			goto fail;
+
+		dev_dbg(&dev->sbd.core,
+			"%s:%u: copy %lu bytes from 0x%p to U0x%p/K0x%p\n",
+			__func__, __LINE__, n, src, userbuf, kernelbuf);
+		if (userbuf) {
+			if (copy_to_user(userbuf, src, n)) {
+				res = -EFAULT;
+				goto fail;
+			}
+			userbuf += n;
+		}
+		if (kernelbuf) {
+			memcpy(kernelbuf, src, n);
+			kernelbuf += n;
+		}
+
+		mutex_unlock(&priv->mutex);
+
+		*pos += n;
+		remaining -= n;
+		sector += priv->chunk_sectors;
+		offset = 0;
+	} while (remaining > 0);
+
+	return count;
+
+fail:
+	mutex_unlock(&priv->mutex);
+	return res;
+}
+
+static ssize_t ps3flash_write(const char __user *userbuf,
+			      const void *kernelbuf, size_t count, loff_t *pos)
+{
+	struct ps3_storage_device *dev = ps3flash_dev;
+	struct ps3flash_private *priv = ps3_system_bus_get_drvdata(&dev->sbd);
+	u64 size, sector, offset;
+	int res = 0;
+	size_t remaining, n;
+	void *dst;
+
+	dev_dbg(&dev->sbd.core,
+		"%s:%u: Writing %zu bytes at position %lld from U0x%p/K0x%p\n",
+		__func__, __LINE__, count, *pos, userbuf, kernelbuf);
+
+	size = dev->regions[dev->region_idx].size*dev->blk_size;
+	if (*pos >= size || !count)
+		return 0;
+
+	if (*pos + count > size) {
+		dev_dbg(&dev->sbd.core,
+			"%s:%u Truncating count from %zu to %llu\n", __func__,
+			__LINE__, count, size - *pos);
+		count = size - *pos;
+	}
+
+	sector = *pos / dev->bounce_size * priv->chunk_sectors;
+	offset = *pos % dev->bounce_size;
+
+	remaining = count;
+	do {
+		n = min_t(u64, remaining, dev->bounce_size - offset);
+		dst = dev->bounce_buf + offset;
+
+		mutex_lock(&priv->mutex);
+
+		if (n != dev->bounce_size)
+			res = ps3flash_fetch(dev, sector);
+		else if (sector != priv->tag)
+			res = ps3flash_writeback(dev);
+		if (res)
+			goto fail;
+
+		dev_dbg(&dev->sbd.core,
+			"%s:%u: copy %lu bytes from U0x%p/K0x%p to 0x%p\n",
+			__func__, __LINE__, n, userbuf, kernelbuf, dst);
+		if (userbuf) {
+			if (copy_from_user(dst, userbuf, n)) {
+				res = -EFAULT;
+				goto fail;
+			}
+			userbuf += n;
+		}
+		if (kernelbuf) {
+			memcpy(dst, kernelbuf, n);
+			kernelbuf += n;
+		}
+
+		priv->tag = sector;
+		priv->dirty = true;
+
+		mutex_unlock(&priv->mutex);
+
+		*pos += n;
+		remaining -= n;
+		sector += priv->chunk_sectors;
+		offset = 0;
+	} while (remaining > 0);
+
+	return count;
+
+fail:
+	mutex_unlock(&priv->mutex);
+	return res;
+}
+
+static ssize_t ps3flash_user_read(struct file *file, char __user *buf,
+				  size_t count, loff_t *pos)
+{
+	return ps3flash_read(buf, NULL, count, pos);
+}
+
+static ssize_t ps3flash_user_write(struct file *file, const char __user *buf,
+				   size_t count, loff_t *pos)
+{
+	return ps3flash_write(buf, NULL, count, pos);
+}
+
+static ssize_t ps3flash_kernel_read(void *buf, size_t count, loff_t pos)
+{
+	return ps3flash_read(NULL, buf, count, &pos);
+}
+
+static ssize_t ps3flash_kernel_write(const void *buf, size_t count,
+				     loff_t pos)
+{
+	ssize_t res;
+	int wb;
+
+	res = ps3flash_write(NULL, buf, count, &pos);
+	if (res < 0)
+		return res;
+
+	/* Make kernel writes synchronous */
+	wb = ps3flash_writeback(ps3flash_dev);
+	if (wb)
+		return wb;
+
+	return res;
+}
+
+static int ps3flash_flush(struct file *file, fl_owner_t id)
+{
+	return ps3flash_writeback(ps3flash_dev);
+}
+
+static int ps3flash_fsync(struct file *file, loff_t start, loff_t end, int datasync)
+{
+	struct inode *inode = file_inode(file);
+	int err;
+	inode_lock(inode);
+	err = ps3flash_writeback(ps3flash_dev);
+	inode_unlock(inode);
+	return err;
+}
+
+static irqreturn_t ps3flash_interrupt(int irq, void *data)
+{
+	struct ps3_storage_device *dev = data;
+	int res;
+	u64 tag, status;
+
+	res = lv1_storage_get_async_status(dev->sbd.dev_id, &tag, &status);
+
+	if (tag != dev->tag)
+		dev_err(&dev->sbd.core,
+			"%s:%u: tag mismatch, got %llx, expected %llx\n",
+			__func__, __LINE__, tag, dev->tag);
+
+	if (res) {
+		dev_err(&dev->sbd.core, "%s:%u: res=%d status=0x%llx\n",
+			__func__, __LINE__, res, status);
+	} else {
+		dev->lv1_status = status;
+		complete(&dev->done);
+	}
+	return IRQ_HANDLED;
+}
+
+static const struct file_operations ps3flash_fops = {
+	.owner	= THIS_MODULE,
+	.llseek	= ps3flash_llseek,
+	.read	= ps3flash_user_read,
+	.write	= ps3flash_user_write,
+	.flush	= ps3flash_flush,
+	.fsync	= ps3flash_fsync,
+};
+
+static const struct ps3_os_area_flash_ops ps3flash_kernel_ops = {
+	.read	= ps3flash_kernel_read,
+	.write	= ps3flash_kernel_write,
+};
+
+static struct miscdevice ps3flash_misc = {
+	.minor	= MISC_DYNAMIC_MINOR,
+	.name	= DEVICE_NAME,
+	.fops	= &ps3flash_fops,
+};
+
+static int ps3flash_probe(struct ps3_system_bus_device *_dev)
+{
+	struct ps3_storage_device *dev = to_ps3_storage_device(&_dev->core);
+	struct ps3flash_private *priv;
+	int error;
+	unsigned long tmp;
+
+	tmp = dev->regions[dev->region_idx].start*dev->blk_size;
+	if (tmp % FLASH_BLOCK_SIZE) {
+		dev_err(&dev->sbd.core,
+			"%s:%u region start %lu is not aligned\n", __func__,
+			__LINE__, tmp);
+		return -EINVAL;
+	}
+	tmp = dev->regions[dev->region_idx].size*dev->blk_size;
+	if (tmp % FLASH_BLOCK_SIZE) {
+		dev_err(&dev->sbd.core,
+			"%s:%u region size %lu is not aligned\n", __func__,
+			__LINE__, tmp);
+		return -EINVAL;
+	}
+
+	/* use static buffer, kmalloc cannot allocate 256 KiB */
+	if (!ps3flash_bounce_buffer.address)
+		return -ENODEV;
+
+	if (ps3flash_dev) {
+		dev_err(&dev->sbd.core,
+			"Only one FLASH device is supported\n");
+		return -EBUSY;
+	}
+
+	ps3flash_dev = dev;
+
+	priv = kzalloc_obj(*priv);
+	if (!priv) {
+		error = -ENOMEM;
+		goto fail;
+	}
+
+	ps3_system_bus_set_drvdata(&dev->sbd, priv);
+	mutex_init(&priv->mutex);
+	priv->tag = -1;
+
+	dev->bounce_size = ps3flash_bounce_buffer.size;
+	dev->bounce_buf = ps3flash_bounce_buffer.address;
+	priv->chunk_sectors = dev->bounce_size / dev->blk_size;
+
+	error = ps3stor_setup(dev, ps3flash_interrupt);
+	if (error)
+		goto fail_free_priv;
+
+	ps3flash_misc.parent = &dev->sbd.core;
+	error = misc_register(&ps3flash_misc);
+	if (error) {
+		dev_err(&dev->sbd.core, "%s:%u: misc_register failed %d\n",
+			__func__, __LINE__, error);
+		goto fail_teardown;
+	}
+
+	dev_info(&dev->sbd.core, "%s:%u: registered misc device %d\n",
+		 __func__, __LINE__, ps3flash_misc.minor);
+
+	ps3_os_area_flash_register(&ps3flash_kernel_ops);
+	return 0;
+
+fail_teardown:
+	ps3stor_teardown(dev);
+fail_free_priv:
+	kfree(priv);
+	ps3_system_bus_set_drvdata(&dev->sbd, NULL);
+fail:
+	ps3flash_dev = NULL;
+	return error;
+}
+
+static void ps3flash_remove(struct ps3_system_bus_device *_dev)
+{
+	struct ps3_storage_device *dev = to_ps3_storage_device(&_dev->core);
+
+	ps3_os_area_flash_register(NULL);
+	misc_deregister(&ps3flash_misc);
+	ps3stor_teardown(dev);
+	kfree(ps3_system_bus_get_drvdata(&dev->sbd));
+	ps3_system_bus_set_drvdata(&dev->sbd, NULL);
+	ps3flash_dev = NULL;
+}
+
+
+static struct ps3_system_bus_driver ps3flash = {
+	.match_id	= PS3_MATCH_ID_STOR_FLASH,
+	.core.name	= DEVICE_NAME,
+	.core.owner	= THIS_MODULE,
+	.probe		= ps3flash_probe,
+	.remove		= ps3flash_remove,
+	.shutdown	= ps3flash_remove,
+};
+
+
+static int __init ps3flash_init(void)
+{
+	return ps3_system_bus_driver_register(&ps3flash);
+}
+
+static void __exit ps3flash_exit(void)
+{
+	ps3_system_bus_driver_unregister(&ps3flash);
+}
+
+module_init(ps3flash_init);
+module_exit(ps3flash_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("PS3 FLASH ROM Storage Driver");
+MODULE_AUTHOR("Sony Corporation");
+MODULE_ALIAS(PS3_MODULE_ALIAS_STOR_FLASH);