From 5febf432df1cfa5b25d99b54c32103fafbdd0eb9 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Sun, 16 Aug 2026 15:32:33 +0200 Subject: kbuild: rust: keep Rust objects out of Clang LTO with inline helpers 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 Cc: Boqun Feng Cc: Alice Ryhl Cc: Matthew Maurer Cc: Josh Poimboeuf Cc: Peter Zijlstra Cc: stable@vger.kernel.org Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust") Acked-by: Gary Guo Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda --- Documentation/usb/functionfs-desc.rst | 39 +++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) create mode 100644 Documentation/usb/functionfs-desc.rst (limited to 'Documentation/usb/functionfs-desc.rst') diff --git a/Documentation/usb/functionfs-desc.rst b/Documentation/usb/functionfs-desc.rst new file mode 100644 index 000000000..39649774d --- /dev/null +++ b/Documentation/usb/functionfs-desc.rst @@ -0,0 +1,39 @@ +====================== +FunctionFS Descriptors +====================== + +Some of the descriptors that can be written to the FFS gadget are +described below. Device and configuration descriptors are handled +by the composite gadget and are not written by the user to the +FFS gadget. + +Descriptors are written to the "ep0" file in the FFS gadget +following the descriptor header. + +.. kernel-doc:: include/uapi/linux/usb/functionfs.h + :doc: descriptors + +Interface Descriptors +--------------------- + +Standard USB interface descriptors may be written. The class/subclass of the +most recent interface descriptor determines what type of class-specific +descriptors are accepted. + +Class-Specific Descriptors +-------------------------- + +Class-specific descriptors are accepted only for the class/subclass of the +most recent interface descriptor. The following are some of the +class-specific descriptors that are supported. + +DFU Functional Descriptor +~~~~~~~~~~~~~~~~~~~~~~~~~ + +When the interface class is USB_CLASS_APP_SPEC and the interface subclass +is USB_SUBCLASS_DFU, a DFU functional descriptor can be provided. +The DFU functional descriptor is a described in the USB specification for +Device Firmware Upgrade (DFU), version 1.1 as of this writing. + +.. kernel-doc:: include/uapi/linux/usb/functionfs.h + :doc: usb_dfu_functional_descriptor -- cgit v1.3.1