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, 123 insertions, 0 deletions

diff --git a/net/hsr/hsr_debugfs.c b/net/hsr/hsr_debugfs.c
new file mode 100644
index 000000000..5b2cfac3b
--- /dev/null
+++ b/net/hsr/hsr_debugfs.c
@@ -0,0 +1,123 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * debugfs code for HSR & PRP
+ * Copyright (C) 2019 Texas Instruments Incorporated
+ *
+ * Author(s):
+ *	Murali Karicheri <m-karicheri2@ti.com>
+ */
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <linux/debugfs.h>
+#include "hsr_main.h"
+#include "hsr_framereg.h"
+
+static struct dentry *hsr_debugfs_root_dir;
+
+/* hsr_node_table_show - Formats and prints node_table entries */
+static int
+hsr_node_table_show(struct seq_file *sfp, void *data)
+{
+	struct hsr_priv *priv = (struct hsr_priv *)sfp->private;
+	struct hsr_node *node;
+
+	seq_printf(sfp, "Node Table entries for (%s) device\n",
+		   (priv->prot_version == PRP_V1 ? "PRP" : "HSR"));
+	seq_puts(sfp, "MAC-Address-A,    MAC-Address-B,    time_in[A], ");
+	seq_puts(sfp, "time_in[B], Address-B port, ");
+	if (priv->prot_version == PRP_V1)
+		seq_puts(sfp, "SAN-A, SAN-B, DAN-P\n");
+	else
+		seq_puts(sfp, "DAN-H\n");
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(node, &priv->node_db, mac_list) {
+		/* skip self node */
+		if (hsr_addr_is_self(priv, node->macaddress_A))
+			continue;
+		seq_printf(sfp, "%pM ", &node->macaddress_A[0]);
+		seq_printf(sfp, "%pM ", &node->macaddress_B[0]);
+		seq_printf(sfp, "%10lx, ", node->time_in[HSR_PT_SLAVE_A]);
+		seq_printf(sfp, "%10lx, ", node->time_in[HSR_PT_SLAVE_B]);
+		seq_printf(sfp, "%14x, ", node->addr_B_port);
+
+		if (priv->prot_version == PRP_V1)
+			seq_printf(sfp, "%5x, %5x, %5x\n",
+				   node->san_a, node->san_b,
+				   (node->san_a == 0 && node->san_b == 0));
+		else
+			seq_printf(sfp, "%5x\n", 1);
+	}
+	rcu_read_unlock();
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(hsr_node_table);
+
+void hsr_debugfs_rename(struct net_device *dev)
+{
+	struct hsr_priv *priv = netdev_priv(dev);
+	int err;
+
+	err = debugfs_change_name(priv->node_tbl_root, "%s", dev->name);
+	if (err)
+		netdev_warn(dev, "failed to rename\n");
+}
+
+/* hsr_debugfs_init - create hsr node_table file for dumping
+ * the node table
+ *
+ * Description:
+ * When debugfs is configured this routine sets up the node_table file per
+ * hsr device for dumping the node_table entries
+ */
+void hsr_debugfs_init(struct hsr_priv *priv, struct net_device *hsr_dev)
+{
+	struct dentry *de = NULL;
+
+	de = debugfs_create_dir(hsr_dev->name, hsr_debugfs_root_dir);
+	if (IS_ERR(de)) {
+		pr_err("Cannot create hsr debugfs directory\n");
+		return;
+	}
+
+	priv->node_tbl_root = de;
+
+	de = debugfs_create_file("node_table", S_IFREG | 0444,
+				 priv->node_tbl_root, priv,
+				 &hsr_node_table_fops);
+	if (IS_ERR(de)) {
+		pr_err("Cannot create hsr node_table file\n");
+		debugfs_remove(priv->node_tbl_root);
+		priv->node_tbl_root = NULL;
+		return;
+	}
+}
+
+/* hsr_debugfs_term - Tear down debugfs intrastructure
+ *
+ * Description:
+ * When Debugfs is configured this routine removes debugfs file system
+ * elements that are specific to hsr
+ */
+void
+hsr_debugfs_term(struct hsr_priv *priv)
+{
+	debugfs_remove_recursive(priv->node_tbl_root);
+	priv->node_tbl_root = NULL;
+}
+
+void hsr_debugfs_create_root(void)
+{
+	hsr_debugfs_root_dir = debugfs_create_dir("hsr", NULL);
+	if (IS_ERR(hsr_debugfs_root_dir)) {
+		pr_err("Cannot create hsr debugfs root directory\n");
+		hsr_debugfs_root_dir = NULL;
+	}
+}
+
+void hsr_debugfs_remove_root(void)
+{
+	/* debugfs_remove() internally checks NULL and ERROR */
+	debugfs_remove(hsr_debugfs_root_dir);
+}