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, 313 insertions, 0 deletions

diff --git a/drivers/usb/chipidea/debug.c b/drivers/usb/chipidea/debug.c
new file mode 100644
index 000000000..e72c43615
--- /dev/null
+++ b/drivers/usb/chipidea/debug.c
@@ -0,0 +1,313 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/device.h>
+#include <linux/types.h>
+#include <linux/spinlock.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+#include <linux/uaccess.h>
+#include <linux/usb/ch9.h>
+#include <linux/usb/gadget.h>
+#include <linux/usb/phy.h>
+#include <linux/usb/otg.h>
+#include <linux/usb/otg-fsm.h>
+#include <linux/usb/chipidea.h>
+
+#include "ci.h"
+#include "udc.h"
+#include "bits.h"
+#include "otg.h"
+
+/*
+ * ci_device_show: prints information about device capabilities and status
+ */
+static int ci_device_show(struct seq_file *s, void *data)
+{
+	struct ci_hdrc *ci = s->private;
+	struct usb_gadget *gadget = &ci->gadget;
+
+	seq_printf(s, "speed             = %d\n", gadget->speed);
+	seq_printf(s, "max_speed         = %d\n", gadget->max_speed);
+	seq_printf(s, "is_otg            = %d\n", gadget->is_otg);
+	seq_printf(s, "is_a_peripheral   = %d\n", gadget->is_a_peripheral);
+	seq_printf(s, "b_hnp_enable      = %d\n", gadget->b_hnp_enable);
+	seq_printf(s, "a_hnp_support     = %d\n", gadget->a_hnp_support);
+	seq_printf(s, "a_alt_hnp_support = %d\n", gadget->a_alt_hnp_support);
+	seq_printf(s, "name              = %s\n",
+		   (gadget->name ? gadget->name : ""));
+
+	if (!ci->driver)
+		return 0;
+
+	seq_printf(s, "gadget function   = %s\n",
+		       (ci->driver->function ? ci->driver->function : ""));
+	seq_printf(s, "gadget max speed  = %d\n", ci->driver->max_speed);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(ci_device);
+
+/*
+ * ci_port_test_show: reads port test mode
+ */
+static int ci_port_test_show(struct seq_file *s, void *data)
+{
+	struct ci_hdrc *ci = s->private;
+	unsigned long flags;
+	unsigned mode;
+
+	pm_runtime_get_sync(ci->dev);
+	spin_lock_irqsave(&ci->lock, flags);
+	mode = hw_port_test_get(ci);
+	spin_unlock_irqrestore(&ci->lock, flags);
+	pm_runtime_put_sync(ci->dev);
+
+	seq_printf(s, "mode = %u\n", mode);
+
+	return 0;
+}
+
+/*
+ * ci_port_test_write: writes port test mode
+ */
+static ssize_t ci_port_test_write(struct file *file, const char __user *ubuf,
+				  size_t count, loff_t *ppos)
+{
+	struct seq_file *s = file->private_data;
+	struct ci_hdrc *ci = s->private;
+	unsigned long flags;
+	unsigned mode;
+	char buf[32];
+	int ret;
+
+	count = min_t(size_t, sizeof(buf) - 1, count);
+	if (copy_from_user(buf, ubuf, count))
+		return -EFAULT;
+
+	/* sscanf requires a zero terminated string */
+	buf[count] = '\0';
+
+	if (sscanf(buf, "%u", &mode) != 1)
+		return -EINVAL;
+
+	if (mode > 255)
+		return -EBADRQC;
+
+	pm_runtime_get_sync(ci->dev);
+	spin_lock_irqsave(&ci->lock, flags);
+	ret = hw_port_test_set(ci, mode);
+	spin_unlock_irqrestore(&ci->lock, flags);
+	pm_runtime_put_sync(ci->dev);
+
+	return ret ? ret : count;
+}
+
+static int ci_port_test_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, ci_port_test_show, inode->i_private);
+}
+
+static const struct file_operations ci_port_test_fops = {
+	.open		= ci_port_test_open,
+	.write		= ci_port_test_write,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+/*
+ * ci_qheads_show: DMA contents of all queue heads
+ */
+static int ci_qheads_show(struct seq_file *s, void *data)
+{
+	struct ci_hdrc *ci = s->private;
+	unsigned long flags;
+	unsigned i, j;
+
+	if (ci->role != CI_ROLE_GADGET) {
+		seq_printf(s, "not in gadget mode\n");
+		return 0;
+	}
+
+	spin_lock_irqsave(&ci->lock, flags);
+	for (i = 0; i < ci->hw_ep_max/2; i++) {
+		struct ci_hw_ep *hweprx = &ci->ci_hw_ep[i];
+		struct ci_hw_ep *hweptx =
+			&ci->ci_hw_ep[i + ci->hw_ep_max/2];
+		seq_printf(s, "EP=%02i: RX=%08X TX=%08X\n",
+			   i, (u32)hweprx->qh.dma, (u32)hweptx->qh.dma);
+		for (j = 0; j < (sizeof(struct ci_hw_qh)/sizeof(u32)); j++)
+			seq_printf(s, " %04X:    %08X    %08X\n", j,
+				   *((u32 *)hweprx->qh.ptr + j),
+				   *((u32 *)hweptx->qh.ptr + j));
+	}
+	spin_unlock_irqrestore(&ci->lock, flags);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(ci_qheads);
+
+/*
+ * ci_requests_show: DMA contents of all requests currently queued (all endpts)
+ */
+static int ci_requests_show(struct seq_file *s, void *data)
+{
+	struct ci_hdrc *ci = s->private;
+	unsigned long flags;
+	struct ci_hw_req *req = NULL;
+	struct td_node *node, *tmpnode;
+	unsigned i, j, qsize = sizeof(struct ci_hw_td)/sizeof(u32);
+
+	if (ci->role != CI_ROLE_GADGET) {
+		seq_printf(s, "not in gadget mode\n");
+		return 0;
+	}
+
+	spin_lock_irqsave(&ci->lock, flags);
+	for (i = 0; i < ci->hw_ep_max; i++)
+		list_for_each_entry(req, &ci->ci_hw_ep[i].qh.queue, queue) {
+			list_for_each_entry_safe(node, tmpnode, &req->tds, td) {
+				seq_printf(s, "EP=%02i: TD=%08X %s\n",
+					   i % (ci->hw_ep_max / 2),
+					   (u32)node->dma,
+					   ((i < ci->hw_ep_max/2) ?
+					   "RX" : "TX"));
+
+				for (j = 0; j < qsize; j++)
+					seq_printf(s, " %04X:    %08X\n", j,
+						   *((u32 *)node->ptr + j));
+			}
+		}
+	spin_unlock_irqrestore(&ci->lock, flags);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(ci_requests);
+
+static int ci_otg_show(struct seq_file *s, void *unused)
+{
+	struct ci_hdrc *ci = s->private;
+	struct otg_fsm *fsm;
+
+	if (!ci || !ci_otg_is_fsm_mode(ci))
+		return 0;
+
+	fsm = &ci->fsm;
+
+	/* ------ State ----- */
+	seq_printf(s, "OTG state: %s\n\n",
+			usb_otg_state_string(ci->otg.state));
+
+	/* ------ State Machine Variables ----- */
+	seq_printf(s, "a_bus_drop: %d\n", fsm->a_bus_drop);
+
+	seq_printf(s, "a_bus_req: %d\n", fsm->a_bus_req);
+
+	seq_printf(s, "a_srp_det: %d\n", fsm->a_srp_det);
+
+	seq_printf(s, "a_vbus_vld: %d\n", fsm->a_vbus_vld);
+
+	seq_printf(s, "b_conn: %d\n", fsm->b_conn);
+
+	seq_printf(s, "adp_change: %d\n", fsm->adp_change);
+
+	seq_printf(s, "power_up: %d\n", fsm->power_up);
+
+	seq_printf(s, "a_bus_resume: %d\n", fsm->a_bus_resume);
+
+	seq_printf(s, "a_bus_suspend: %d\n", fsm->a_bus_suspend);
+
+	seq_printf(s, "a_conn: %d\n", fsm->a_conn);
+
+	seq_printf(s, "b_bus_req: %d\n", fsm->b_bus_req);
+
+	seq_printf(s, "b_bus_suspend: %d\n", fsm->b_bus_suspend);
+
+	seq_printf(s, "b_se0_srp: %d\n", fsm->b_se0_srp);
+
+	seq_printf(s, "b_ssend_srp: %d\n", fsm->b_ssend_srp);
+
+	seq_printf(s, "b_sess_vld: %d\n", fsm->b_sess_vld);
+
+	seq_printf(s, "b_srp_done: %d\n", fsm->b_srp_done);
+
+	seq_printf(s, "drv_vbus: %d\n", fsm->drv_vbus);
+
+	seq_printf(s, "loc_conn: %d\n", fsm->loc_conn);
+
+	seq_printf(s, "loc_sof: %d\n", fsm->loc_sof);
+
+	seq_printf(s, "adp_prb: %d\n", fsm->adp_prb);
+
+	seq_printf(s, "id: %d\n", fsm->id);
+
+	seq_printf(s, "protocol: %d\n", fsm->protocol);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(ci_otg);
+
+static int ci_registers_show(struct seq_file *s, void *unused)
+{
+	struct ci_hdrc *ci = s->private;
+	u32 tmp_reg;
+
+	if (!ci || ci->in_lpm)
+		return -EPERM;
+
+	/* ------ Registers ----- */
+	tmp_reg = hw_read_intr_enable(ci);
+	seq_printf(s, "USBINTR reg: %08x\n", tmp_reg);
+
+	tmp_reg = hw_read_intr_status(ci);
+	seq_printf(s, "USBSTS reg: %08x\n", tmp_reg);
+
+	tmp_reg = hw_read(ci, OP_USBMODE, ~0);
+	seq_printf(s, "USBMODE reg: %08x\n", tmp_reg);
+
+	tmp_reg = hw_read(ci, OP_USBCMD, ~0);
+	seq_printf(s, "USBCMD reg: %08x\n", tmp_reg);
+
+	tmp_reg = hw_read(ci, OP_PORTSC, ~0);
+	seq_printf(s, "PORTSC reg: %08x\n", tmp_reg);
+
+	if (ci->is_otg) {
+		tmp_reg = hw_read_otgsc(ci, ~0);
+		seq_printf(s, "OTGSC reg: %08x\n", tmp_reg);
+	}
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(ci_registers);
+
+/**
+ * dbg_create_files: initializes the attribute interface
+ * @ci: device
+ *
+ * This function returns an error code
+ */
+void dbg_create_files(struct ci_hdrc *ci)
+{
+	struct dentry *dir;
+
+	dir = debugfs_create_dir(dev_name(ci->dev), usb_debug_root);
+
+	debugfs_create_file("device", S_IRUGO, dir, ci, &ci_device_fops);
+	debugfs_create_file("port_test", S_IRUGO | S_IWUSR, dir, ci, &ci_port_test_fops);
+	debugfs_create_file("qheads", S_IRUGO, dir, ci, &ci_qheads_fops);
+	debugfs_create_file("requests", S_IRUGO, dir, ci, &ci_requests_fops);
+
+	if (ci_otg_is_fsm_mode(ci))
+		debugfs_create_file("otg", S_IRUGO, dir, ci, &ci_otg_fops);
+
+	debugfs_create_file("registers", S_IRUGO, dir, ci, &ci_registers_fops);
+}
+
+/**
+ * dbg_remove_files: destroys the attribute interface
+ * @ci: device
+ */
+void dbg_remove_files(struct ci_hdrc *ci)
+{
+	debugfs_lookup_and_remove(dev_name(ci->dev), usb_debug_root);
+}