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, 62 insertions, 0 deletions

diff --git a/drivers/usb/isp1760/Kconfig b/drivers/usb/isp1760/Kconfig
new file mode 100644
index 000000000..e19178f3c
--- /dev/null
+++ b/drivers/usb/isp1760/Kconfig
@@ -0,0 +1,62 @@
+# SPDX-License-Identifier: GPL-2.0
+
+config USB_ISP1760
+	tristate "NXP ISP 1760/1761/1763 support"
+	depends on USB || USB_GADGET
+	select REGMAP_MMIO
+	help
+	  Say Y or M here if your system as an ISP1760/1763 USB host controller
+	  or an ISP1761 USB dual-role controller.
+
+	  This driver does not support isochronous transfers or OTG.
+	  This USB controller is usually attached to a non-DMA-Master
+	  capable bus. NXP's eval kit brings this chip on PCI card
+	  where the chip itself is behind a PLB to simulate such
+	  a bus.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called isp1760.
+
+config USB_ISP1760_HCD
+	bool
+
+config USB_ISP1761_UDC
+	bool
+
+if USB_ISP1760
+
+choice
+	prompt "ISP1760 Mode Selection"
+	default USB_ISP1760_DUAL_ROLE if (USB && USB_GADGET)
+	default USB_ISP1760_HOST_ROLE if (USB && !USB_GADGET)
+	default USB_ISP1760_GADGET_ROLE if (!USB && USB_GADGET)
+
+config USB_ISP1760_HOST_ROLE
+	bool "Host only mode"
+	depends on USB=y || USB=USB_ISP1760
+	select USB_ISP1760_HCD
+	help
+	  Select this if you want to use the ISP1760 in host mode only. The
+	  gadget function will be disabled.
+
+config USB_ISP1760_GADGET_ROLE
+	bool "Gadget only mode"
+	depends on USB_GADGET=y || USB_GADGET=USB_ISP1760
+	select USB_ISP1761_UDC
+	help
+	  Select this if you want to use the ISP1760 in peripheral mode only.
+	  The host function will be disabled.
+
+config USB_ISP1760_DUAL_ROLE
+	bool "Dual Role mode"
+	depends on USB=y || USB=USB_ISP1760
+	depends on USB_GADGET=y || USB_GADGET=USB_ISP1760
+	select USB_ISP1760_HCD
+	select USB_ISP1761_UDC
+	help
+	  Select this if you want to use the ISP1760 in both host and
+	  peripheral modes.
+
+endchoice
+
+endif