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, 97 insertions, 0 deletions

diff --git a/drivers/usb/dwc2/Kconfig b/drivers/usb/dwc2/Kconfig
new file mode 100644
index 000000000..d7af55a8e
--- /dev/null
+++ b/drivers/usb/dwc2/Kconfig
@@ -0,0 +1,97 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config USB_DWC2
+	tristate "DesignWare USB2 DRD Core Support"
+	depends on HAS_DMA
+	depends on USB || USB_GADGET
+	depends on HAS_IOMEM
+	select USB_ROLE_SWITCH
+	help
+	  Say Y here if your system has a Dual Role Hi-Speed USB
+	  controller based on the DesignWare HSOTG IP Core.
+
+	  For host mode, if you choose to build the driver as dynamically
+	  linked modules, the core module will be called dwc2.ko, the PCI
+	  bus interface module (if you have a PCI bus system) will be
+	  called dwc2_pci.ko, and the platform interface module (for
+	  controllers directly connected to the CPU) will be called
+	  dwc2_platform.ko. For all modes(host, gadget and dual-role), there
+	  will be an additional module named dwc2.ko.
+
+if USB_DWC2
+
+choice
+	prompt "DWC2 Mode Selection"
+	default USB_DWC2_DUAL_ROLE if (USB && USB_GADGET)
+	default USB_DWC2_HOST if (USB && !USB_GADGET)
+	default USB_DWC2_PERIPHERAL if (!USB && USB_GADGET)
+
+config USB_DWC2_HOST
+	bool "Host only mode"
+	depends on USB=y || (USB_DWC2=m && USB)
+	help
+	  The Designware USB2.0 high-speed host controller
+	  integrated into many SoCs. Select this option if you want the
+	  driver to operate in Host-only mode.
+
+comment "Gadget/Dual-role mode requires USB Gadget support to be enabled"
+
+config USB_DWC2_PERIPHERAL
+	bool "Gadget only mode"
+	depends on USB_GADGET=y || USB_GADGET=USB_DWC2
+	help
+	  The Designware USB2.0 high-speed gadget controller
+	  integrated into many SoCs. Select this option if you want the
+	  driver to operate in Peripheral-only mode. This option requires
+	  USB_GADGET to be enabled.
+
+config USB_DWC2_DUAL_ROLE
+	bool "Dual Role mode"
+	depends on (USB=y && USB_GADGET=y) || (USB_DWC2=m && USB && USB_GADGET)
+	help
+	  Select this option if you want the driver to work in a dual-role
+	  mode. In this mode both host and gadget features are enabled, and
+	  the role will be determined by the cable that gets plugged-in. This
+	  option requires USB_GADGET to be enabled.
+endchoice
+
+config USB_DWC2_PCI
+	tristate "DWC2 PCI"
+	depends on USB_PCI
+	depends on USB_GADGET || !USB_GADGET
+	select NOP_USB_XCEIV
+	help
+	  The Designware USB2.0 PCI interface module for controllers
+	  connected to a PCI bus.
+
+config USB_DWC2_DEBUG
+	bool "Enable Debugging Messages"
+	help
+	  Say Y here to enable debugging messages in the DWC2 Driver.
+
+config USB_DWC2_VERBOSE
+	bool "Enable Verbose Debugging Messages"
+	depends on USB_DWC2_DEBUG
+	help
+	  Say Y here to enable verbose debugging messages in the DWC2 Driver.
+	  WARNING: Enabling this will quickly fill your message log.
+	  If in doubt, say N.
+
+config USB_DWC2_TRACK_MISSED_SOFS
+	bool "Enable Missed SOF Tracking"
+	help
+	  Say Y here to enable logging of missed SOF events to the dmesg log.
+	  WARNING: This feature is still experimental.
+	  If in doubt, say N.
+
+config USB_DWC2_DEBUG_PERIODIC
+	bool "Enable Debugging Messages For Periodic Transfers"
+	depends on USB_DWC2_DEBUG || USB_DWC2_VERBOSE
+	default y
+	help
+	  Say N here to disable (verbose) debugging messages to be
+	  logged for periodic transfers. This allows better debugging of
+	  non-periodic transfers, but of course the debug logs will be
+	  incomplete. Note that this also disables some debug messages
+	  for which the transfer type cannot be deduced.
+endif