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, 154 insertions, 0 deletions

diff --git a/drivers/edac/debugfs.c b/drivers/edac/debugfs.c
new file mode 100644
index 000000000..8195fc9c9
--- /dev/null
+++ b/drivers/edac/debugfs.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/string_choices.h>
+
+#include "edac_module.h"
+
+static struct dentry *edac_debugfs;
+
+static ssize_t edac_fake_inject_write(struct file *file,
+				      const char __user *data,
+				      size_t count, loff_t *ppos)
+{
+	struct device *dev = file->private_data;
+	struct mem_ctl_info *mci = to_mci(dev);
+	static enum hw_event_mc_err_type type;
+	u16 errcount = mci->fake_inject_count;
+
+	if (!errcount)
+		errcount = 1;
+
+	type = mci->fake_inject_ue ? HW_EVENT_ERR_UNCORRECTED
+				   : HW_EVENT_ERR_CORRECTED;
+
+	printk(KERN_DEBUG
+	       "Generating %d %s fake error%s to %d.%d.%d to test core handling. NOTE: this won't test the driver-specific decoding logic.\n",
+		errcount,
+		(type == HW_EVENT_ERR_UNCORRECTED) ? "UE" : "CE",
+		str_plural(errcount),
+		mci->fake_inject_layer[0],
+		mci->fake_inject_layer[1],
+		mci->fake_inject_layer[2]
+	       );
+	edac_mc_handle_error(type, mci, errcount, 0, 0, 0,
+			     mci->fake_inject_layer[0],
+			     mci->fake_inject_layer[1],
+			     mci->fake_inject_layer[2],
+			     "FAKE ERROR", "for EDAC testing only");
+
+	return count;
+}
+
+static const struct file_operations debug_fake_inject_fops = {
+	.open = simple_open,
+	.write = edac_fake_inject_write,
+	.llseek = generic_file_llseek,
+};
+
+void __init edac_debugfs_init(void)
+{
+	edac_debugfs = debugfs_create_dir("edac", NULL);
+}
+
+void edac_debugfs_exit(void)
+{
+	debugfs_remove_recursive(edac_debugfs);
+}
+
+void edac_create_debugfs_nodes(struct mem_ctl_info *mci)
+{
+	struct dentry *parent;
+	char name[80];
+	int i;
+
+	parent = debugfs_create_dir(mci->dev.kobj.name, edac_debugfs);
+
+	for (i = 0; i < mci->n_layers; i++) {
+		sprintf(name, "fake_inject_%s",
+			     edac_layer_name[mci->layers[i].type]);
+		debugfs_create_u8(name, S_IRUGO | S_IWUSR, parent,
+				  &mci->fake_inject_layer[i]);
+	}
+
+	debugfs_create_bool("fake_inject_ue", S_IRUGO | S_IWUSR, parent,
+			    &mci->fake_inject_ue);
+
+	debugfs_create_u16("fake_inject_count", S_IRUGO | S_IWUSR, parent,
+			   &mci->fake_inject_count);
+
+	debugfs_create_file("fake_inject", S_IWUSR, parent, &mci->dev,
+			    &debug_fake_inject_fops);
+
+	mci->debugfs = parent;
+}
+
+/* Create a toplevel dir under EDAC's debugfs hierarchy */
+struct dentry *edac_debugfs_create_dir(const char *dirname)
+{
+	if (!edac_debugfs)
+		return NULL;
+
+	return debugfs_create_dir(dirname, edac_debugfs);
+}
+EXPORT_SYMBOL_GPL(edac_debugfs_create_dir);
+
+/* Create a toplevel dir under EDAC's debugfs hierarchy with parent @parent */
+struct dentry *
+edac_debugfs_create_dir_at(const char *dirname, struct dentry *parent)
+{
+	return debugfs_create_dir(dirname, parent);
+}
+EXPORT_SYMBOL_GPL(edac_debugfs_create_dir_at);
+
+/*
+ * Create a file under EDAC's hierarchy or a sub-hierarchy:
+ *
+ * @name: file name
+ * @mode: file permissions
+ * @parent: parent dentry. If NULL, it becomes the toplevel EDAC dir
+ * @data: private data of caller
+ * @fops: file operations of this file
+ */
+struct dentry *
+edac_debugfs_create_file(const char *name, umode_t mode, struct dentry *parent,
+			 void *data, const struct file_operations *fops)
+{
+	if (!parent)
+		parent = edac_debugfs;
+
+	return debugfs_create_file(name, mode, parent, data, fops);
+}
+EXPORT_SYMBOL_GPL(edac_debugfs_create_file);
+
+/* Wrapper for debugfs_create_x8() */
+void edac_debugfs_create_x8(const char *name, umode_t mode,
+			    struct dentry *parent, u8 *value)
+{
+	if (!parent)
+		parent = edac_debugfs;
+
+	debugfs_create_x8(name, mode, parent, value);
+}
+EXPORT_SYMBOL_GPL(edac_debugfs_create_x8);
+
+/* Wrapper for debugfs_create_x16() */
+void edac_debugfs_create_x16(const char *name, umode_t mode,
+			     struct dentry *parent, u16 *value)
+{
+	if (!parent)
+		parent = edac_debugfs;
+
+	debugfs_create_x16(name, mode, parent, value);
+}
+EXPORT_SYMBOL_GPL(edac_debugfs_create_x16);
+
+/* Wrapper for debugfs_create_x32() */
+void edac_debugfs_create_x32(const char *name, umode_t mode,
+			     struct dentry *parent, u32 *value)
+{
+	if (!parent)
+		parent = edac_debugfs;
+
+	debugfs_create_x32(name, mode, parent, value);
+}
+EXPORT_SYMBOL_GPL(edac_debugfs_create_x32);