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, 168 insertions, 0 deletions

diff --git a/drivers/usb/host/ehci-sysfs.c b/drivers/usb/host/ehci-sysfs.c
new file mode 100644
index 000000000..5e6b545c3
--- /dev/null
+++ b/drivers/usb/host/ehci-sysfs.c
@@ -0,0 +1,168 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2007 by Alan Stern
+ */
+
+/* this file is part of ehci-hcd.c */
+
+
+/* Display the ports dedicated to the companion controller */
+static ssize_t companion_show(struct device *dev,
+			      struct device_attribute *attr,
+			      char *buf)
+{
+	struct ehci_hcd		*ehci;
+	int			nports, index;
+	int			len = 0;
+
+	ehci = hcd_to_ehci(dev_get_drvdata(dev));
+	nports = HCS_N_PORTS(ehci->hcs_params);
+
+	for (index = 0; index < nports; ++index) {
+		if (test_bit(index, &ehci->companion_ports))
+			len += sysfs_emit_at(buf, len, "%d\n", index + 1);
+	}
+	return len;
+}
+
+/*
+ * Dedicate or undedicate a port to the companion controller.
+ * Syntax is "[-]portnum", where a leading '-' sign means
+ * return control of the port to the EHCI controller.
+ */
+static ssize_t companion_store(struct device *dev,
+			       struct device_attribute *attr,
+			       const char *buf, size_t count)
+{
+	struct ehci_hcd		*ehci;
+	int			portnum, new_owner;
+
+	ehci = hcd_to_ehci(dev_get_drvdata(dev));
+	new_owner = PORT_OWNER;		/* Owned by companion */
+	if (sscanf(buf, "%d", &portnum) != 1)
+		return -EINVAL;
+	if (portnum < 0) {
+		portnum = - portnum;
+		new_owner = 0;		/* Owned by EHCI */
+	}
+	if (portnum <= 0 || portnum > HCS_N_PORTS(ehci->hcs_params))
+		return -ENOENT;
+	portnum--;
+	if (new_owner)
+		set_bit(portnum, &ehci->companion_ports);
+	else
+		clear_bit(portnum, &ehci->companion_ports);
+	set_owner(ehci, portnum, new_owner);
+	return count;
+}
+static DEVICE_ATTR_RW(companion);
+
+
+/*
+ * Display / Set uframe_periodic_max
+ */
+static ssize_t uframe_periodic_max_show(struct device *dev,
+					struct device_attribute *attr,
+					char *buf)
+{
+	struct ehci_hcd		*ehci;
+
+	ehci = hcd_to_ehci(dev_get_drvdata(dev));
+	return sysfs_emit(buf, "%d\n", ehci->uframe_periodic_max);
+}
+
+
+static ssize_t uframe_periodic_max_store(struct device *dev,
+					struct device_attribute *attr,
+					const char *buf, size_t count)
+{
+	struct ehci_hcd		*ehci;
+	unsigned		uframe_periodic_max;
+	unsigned		uframe;
+	unsigned long		flags;
+	ssize_t			ret;
+
+	ehci = hcd_to_ehci(dev_get_drvdata(dev));
+	if (kstrtouint(buf, 0, &uframe_periodic_max) < 0)
+		return -EINVAL;
+
+	if (uframe_periodic_max < 100 || uframe_periodic_max >= 125) {
+		ehci_info(ehci, "rejecting invalid request for "
+				"uframe_periodic_max=%u\n", uframe_periodic_max);
+		return -EINVAL;
+	}
+
+	ret = -EINVAL;
+
+	/*
+	 * lock, so that our checking does not race with possible periodic
+	 * bandwidth allocation through submitting new urbs.
+	 */
+	spin_lock_irqsave (&ehci->lock, flags);
+
+	/*
+	 * for request to decrease max periodic bandwidth, we have to check
+	 * to see whether the decrease is possible.
+	 */
+	if (uframe_periodic_max < ehci->uframe_periodic_max) {
+		u8		allocated_max = 0;
+
+		for (uframe = 0; uframe < EHCI_BANDWIDTH_SIZE; ++uframe)
+			allocated_max = max(allocated_max,
+					ehci->bandwidth[uframe]);
+
+		if (allocated_max > uframe_periodic_max) {
+			ehci_info(ehci,
+				"cannot decrease uframe_periodic_max because "
+				"periodic bandwidth is already allocated "
+				"(%u > %u)\n",
+				allocated_max, uframe_periodic_max);
+			goto out_unlock;
+		}
+	}
+
+	/* increasing is always ok */
+
+	ehci_info(ehci, "setting max periodic bandwidth to %u%% "
+			"(== %u usec/uframe)\n",
+			100*uframe_periodic_max/125, uframe_periodic_max);
+
+	if (uframe_periodic_max != 100)
+		ehci_warn(ehci, "max periodic bandwidth set is non-standard\n");
+
+	ehci->uframe_periodic_max = uframe_periodic_max;
+	ret = count;
+
+out_unlock:
+	spin_unlock_irqrestore (&ehci->lock, flags);
+	return ret;
+}
+static DEVICE_ATTR_RW(uframe_periodic_max);
+
+
+static inline int create_sysfs_files(struct ehci_hcd *ehci)
+{
+	struct device	*controller = ehci_to_hcd(ehci)->self.controller;
+	int	i = 0;
+
+	/* with integrated TT there is no companion! */
+	if (!ehci_is_TDI(ehci))
+		i = device_create_file(controller, &dev_attr_companion);
+	if (i)
+		goto out;
+
+	i = device_create_file(controller, &dev_attr_uframe_periodic_max);
+out:
+	return i;
+}
+
+static inline void remove_sysfs_files(struct ehci_hcd *ehci)
+{
+	struct device	*controller = ehci_to_hcd(ehci)->self.controller;
+
+	/* with integrated TT there is no companion! */
+	if (!ehci_is_TDI(ehci))
+		device_remove_file(controller, &dev_attr_companion);
+
+	device_remove_file(controller, &dev_attr_uframe_periodic_max);
+}