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, 99 insertions, 0 deletions

diff --git a/drivers/parisc/eisa_eeprom.c b/drivers/parisc/eisa_eeprom.c
new file mode 100644
index 000000000..601cbb225
--- /dev/null
+++ b/drivers/parisc/eisa_eeprom.c
@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* 
+ *    EISA "eeprom" support routines
+ *
+ *    Copyright (C) 2001 Thomas Bogendoerfer <tsbogend at parisc-linux.org>
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/miscdevice.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <asm/io.h>
+#include <linux/uaccess.h>
+#include <asm/eisa_eeprom.h>
+
+static loff_t eisa_eeprom_llseek(struct file *file, loff_t offset, int origin)
+{
+	return fixed_size_llseek(file, offset, origin, HPEE_MAX_LENGTH);
+}
+
+static ssize_t eisa_eeprom_read(struct file * file,
+			      char __user *buf, size_t count, loff_t *ppos )
+{
+	unsigned char *tmp;
+	ssize_t ret;
+	int i;
+	
+	if (*ppos < 0 || *ppos >= HPEE_MAX_LENGTH)
+		return 0;
+	
+	count = *ppos + count < HPEE_MAX_LENGTH ? count : HPEE_MAX_LENGTH - *ppos;
+	tmp = kmalloc(count, GFP_KERNEL);
+	if (tmp) {
+		for (i = 0; i < count; i++)
+			tmp[i] = readb(eisa_eeprom_addr+(*ppos)++);
+
+		if (copy_to_user (buf, tmp, count))
+			ret = -EFAULT;
+		else
+			ret = count;
+		kfree (tmp);
+	} else
+		ret = -ENOMEM;
+	
+	return ret;
+}
+
+static int eisa_eeprom_open(struct inode *inode, struct file *file)
+{
+	if (file->f_mode & FMODE_WRITE)
+		return -EINVAL;
+   
+	return 0;
+}
+
+static int eisa_eeprom_release(struct inode *inode, struct file *file)
+{
+	return 0;
+}
+
+/*
+ *	The various file operations we support.
+ */
+static const struct file_operations eisa_eeprom_fops = {
+	.owner =	THIS_MODULE,
+	.llseek =	eisa_eeprom_llseek,
+	.read =		eisa_eeprom_read,
+	.open =		eisa_eeprom_open,
+	.release =	eisa_eeprom_release,
+};
+
+static struct miscdevice eisa_eeprom_dev = {
+	EISA_EEPROM_MINOR,
+	"eisa_eeprom",
+	&eisa_eeprom_fops
+};
+
+static int __init eisa_eeprom_init(void)
+{
+	int retval;
+
+	if (!eisa_eeprom_addr)
+		return -ENODEV;
+
+	retval = misc_register(&eisa_eeprom_dev);
+	if (retval < 0) {
+		printk(KERN_ERR "EISA EEPROM: cannot register misc device.\n");
+		return retval;
+	}
+
+	printk(KERN_INFO "EISA EEPROM at 0x%px\n", eisa_eeprom_addr);
+	return 0;
+}
+
+MODULE_LICENSE("GPL");
+
+module_init(eisa_eeprom_init);