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 --- tools/perf/util/demangle-rust-v0.h | 88 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 88 insertions(+) create mode 100644 tools/perf/util/demangle-rust-v0.h (limited to 'tools/perf/util/demangle-rust-v0.h') diff --git a/tools/perf/util/demangle-rust-v0.h b/tools/perf/util/demangle-rust-v0.h new file mode 100644 index 000000000..d00928186 --- /dev/null +++ b/tools/perf/util/demangle-rust-v0.h @@ -0,0 +1,88 @@ +// SPDX-License-Identifier: Apache-2.0 OR MIT + +// The contents of this file come from the Rust rustc-demangle library, hosted +// in the repository, licensed +// under "Apache-2.0 OR MIT". For copyright details, see +// . +// Please note that the file should be kept as close as possible to upstream. + +#ifndef _H_DEMANGLE_V0_H +#define _H_DEMANGLE_V0_H + +#ifdef __cplusplus +extern "C" { +#endif + +#include + +#if defined(__GNUC__) || defined(__clang__) +#define DEMANGLE_NODISCARD __attribute__((warn_unused_result)) +#else +#define DEMANGLE_NODISCARD +#endif + +typedef enum { + OverflowOk, + OverflowOverflow +} overflow_status; + +enum demangle_style { + DemangleStyleUnknown = 0, + DemangleStyleLegacy, + DemangleStyleV0, +}; + +// Not using a union here to make the struct easier to copy-paste if needed. +struct demangle { + enum demangle_style style; + // points to the "mangled" part of the name, + // not including `ZN` or `R` prefixes. + const char *mangled; + size_t mangled_len; + // In DemangleStyleLegacy, is the number of path elements + size_t elements; + // while it's called "original", it will not contain `.llvm.9D1C9369@@16` suffixes + // that are to be ignored. + const char *original; + size_t original_len; + // Contains the part after the mangled name that is to be outputted, + // which can be `.exit.i.i` suffixes LLVM sometimes adds. + const char *suffix; + size_t suffix_len; +}; + +// if the length of the output buffer is less than `output_len-OVERFLOW_MARGIN`, +// the demangler will return `OverflowOverflow` even if there is no overflow. +#define OVERFLOW_MARGIN 4 + +/// Demangle a C string that refers to a Rust symbol and put the demangle intermediate result in `res`. +/// Beware that `res` contains references into `s`. If `s` is modified (or free'd) before calling +/// `rust_demangle_display_demangle` behavior is undefined. +/// +/// Use `rust_demangle_display_demangle` to convert it to an actual string. +void rust_demangle_demangle(const char *s, struct demangle *res); + +/// Write the string in a `struct demangle` into a buffer. +/// +/// Return `OverflowOk` if the output buffer was sufficiently big, `OverflowOverflow` if it wasn't. +/// This function is `O(n)` in the length of the input + *output* [$], but the demangled output of demangling a symbol can +/// be exponentially[$$] large, therefore it is recommended to have a sane bound (`rust-demangle` +/// uses 1,000,000 bytes) on `len`. +/// +/// `alternate`, if true, uses the less verbose alternate formatting (Rust `{:#}`) is used, which does not show +/// symbol hashes and types of constant ints. +/// +/// [$] It's `O(n * MAX_DEPTH)`, but `MAX_DEPTH` is a constant 300 and therefore it's `O(n)` +/// [$$] Technically, bounded by `O(n^MAX_DEPTH)`, but this is practically exponential. +DEMANGLE_NODISCARD overflow_status rust_demangle_display_demangle(struct demangle const *res, char *out, size_t len, bool alternate); + +/// Returns true if `res` refers to a known valid Rust demangling style, false if it's an unknown style. +bool rust_demangle_is_known(struct demangle *res); + +#undef DEMANGLE_NODISCARD + +#ifdef __cplusplus +} +#endif + +#endif -- cgit v1.3.1