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/llvm-c-helpers.cpp | 196 +++++++++++++++++++++++++++++++++++++ 1 file changed, 196 insertions(+) create mode 100644 tools/perf/util/llvm-c-helpers.cpp (limited to 'tools/perf/util/llvm-c-helpers.cpp') diff --git a/tools/perf/util/llvm-c-helpers.cpp b/tools/perf/util/llvm-c-helpers.cpp new file mode 100644 index 000000000..004081bd1 --- /dev/null +++ b/tools/perf/util/llvm-c-helpers.cpp @@ -0,0 +1,196 @@ +// SPDX-License-Identifier: GPL-2.0 + +/* + * Must come before the linux/compiler.h include, which defines several + * macros (e.g. noinline) that conflict with compiler builtins used + * by LLVM. + */ +#pragma GCC diagnostic push +#pragma GCC diagnostic ignored "-Wunused-parameter" /* Needed for LLVM <= 15 */ +#include +#include +#pragma GCC diagnostic pop + +#include +#include +#include +#include +extern "C" { +#include +} +#include "llvm-c-helpers.h" + +extern "C" +char *dso__demangle_sym(struct dso *dso, int kmodule, const char *elf_name); + +using namespace llvm; +using llvm::symbolize::LLVMSymbolizer; + +/* + * Allocate a static LLVMSymbolizer, which will live to the end of the program. + * Unlike the bfd paths, LLVMSymbolizer has its own cache, so we do not need + * to store anything in the dso struct. + */ +static LLVMSymbolizer *get_symbolizer() +{ + static LLVMSymbolizer *instance = nullptr; + if (instance == nullptr) { + LLVMSymbolizer::Options opts; + /* + * LLVM sometimes demangles slightly different from the rest + * of the code, and this mismatch can cause new_inline_sym() + * to get confused and mark non-inline symbol as inlined + * (since the name does not properly match up with base_sym). + * Thus, disable the demangling and let the rest of the code + * handle it. + */ + opts.Demangle = false; + instance = new LLVMSymbolizer(opts); + } + return instance; +} + +/* Returns 0 on error, 1 on success. */ +static int extract_file_and_line(const DILineInfo &line_info, char **file, + unsigned int *line) +{ + if (file) { + if (line_info.FileName == "") { + /* Match the convention of libbfd. */ + *file = nullptr; + } else { + /* The caller expects to get something it can free(). */ + *file = strdup(line_info.FileName.c_str()); + if (*file == nullptr) + return 0; + } + } + if (line) + *line = line_info.Line; + return 1; +} + +extern "C" +int llvm_addr2line(const char *dso_name, u64 addr, + char **file, unsigned int *line, + bool unwind_inlines, + llvm_a2l_frame **inline_frames) +{ + LLVMSymbolizer *symbolizer = get_symbolizer(); + object::SectionedAddress sectioned_addr = { + addr, + object::SectionedAddress::UndefSection + }; + + if (unwind_inlines) { + Expected res_or_err = + symbolizer->symbolizeInlinedCode(dso_name, + sectioned_addr); + if (!res_or_err) + return 0; + unsigned num_frames = res_or_err->getNumberOfFrames(); + if (num_frames == 0) + return 0; + + if (extract_file_and_line(res_or_err->getFrame(0), + file, line) == 0) + return 0; + + *inline_frames = (llvm_a2l_frame *)calloc( + num_frames, sizeof(**inline_frames)); + if (*inline_frames == nullptr) + return 0; + + for (unsigned i = 0; i < num_frames; ++i) { + const DILineInfo &src = res_or_err->getFrame(i); + + llvm_a2l_frame &dst = (*inline_frames)[i]; + if (src.FileName == "") + /* Match the convention of libbfd. */ + dst.filename = nullptr; + else + dst.filename = strdup(src.FileName.c_str()); + dst.funcname = strdup(src.FunctionName.c_str()); + dst.line = src.Line; + + if (dst.filename == nullptr || + dst.funcname == nullptr) { + for (unsigned j = 0; j <= i; ++j) { + zfree(&(*inline_frames)[j].filename); + zfree(&(*inline_frames)[j].funcname); + } + zfree(inline_frames); + return 0; + } + } + + return num_frames; + } else { + if (inline_frames) + *inline_frames = nullptr; + + Expected res_or_err = + symbolizer->symbolizeCode(dso_name, sectioned_addr); + if (!res_or_err) + return 0; + return extract_file_and_line(*res_or_err, file, line); + } +} + +static char * +make_symbol_relative_string(struct dso *dso, const char *sym_name, + u64 addr, u64 base_addr) +{ + if (!strcmp(sym_name, "")) + return NULL; + + char *demangled = dso__demangle_sym(dso, 0, sym_name); + if (base_addr && base_addr != addr) { + char buf[256]; + snprintf(buf, sizeof(buf), "%s+0x%" PRIx64, + demangled ? demangled : sym_name, addr - base_addr); + free(demangled); + return strdup(buf); + } else { + if (demangled) + return demangled; + else + return strdup(sym_name); + } +} + +extern "C" +char *llvm_name_for_code(struct dso *dso, const char *dso_name, u64 addr) +{ + LLVMSymbolizer *symbolizer = get_symbolizer(); + object::SectionedAddress sectioned_addr = { + addr, + object::SectionedAddress::UndefSection + }; + Expected res_or_err = + symbolizer->symbolizeCode(dso_name, sectioned_addr); + if (!res_or_err) { + return NULL; + } + return make_symbol_relative_string( + dso, res_or_err->FunctionName.c_str(), + addr, res_or_err->StartAddress ? *res_or_err->StartAddress : 0); +} + +extern "C" +char *llvm_name_for_data(struct dso *dso, const char *dso_name, u64 addr) +{ + LLVMSymbolizer *symbolizer = get_symbolizer(); + object::SectionedAddress sectioned_addr = { + addr, + object::SectionedAddress::UndefSection + }; + Expected res_or_err = + symbolizer->symbolizeData(dso_name, sectioned_addr); + if (!res_or_err) { + return NULL; + } + return make_symbol_relative_string( + dso, res_or_err->Name.c_str(), + addr, res_or_err->Start); +} -- cgit v1.3.1