From c3f8644c21df9b7db97eb70e08e2826368aaafa0 Mon Sep 17 00:00:00 2001 From: "Steinar H. Gunderson" Date: Sat, 3 Aug 2024 17:20:06 +0200 Subject: perf report: Support LLVM for addr2line() In addition to the existing support for libbfd and calling out to an external addr2line command, add support for using libllvm directly. This is both faster than libbfd, and can be enabled in distro builds (the LLVM license has an explicit provision for GPLv2 compatibility). Thus, it is set as the primary choice if available. As an example, running 'perf report' on a medium-size profile with DWARF-based backtraces took 58 seconds with LLVM, 78 seconds with libbfd, 153 seconds with external llvm-addr2line, and I got tired and aborted the test after waiting for 55 minutes with external bfd addr2line (which is the default for perf as compiled by distributions today). Evidently, for this case, the bfd addr2line process needs 18 seconds (on a 5.2 GHz Zen 3) to load the .debug ELF in question, hits the 1-second timeout and gets killed during initialization, getting restarted anew every time. Having an in-process addr2line makes this much more robust. As future extensions, libllvm can be used in many other places where we currently use libbfd or other libraries: - Symbol enumeration (in particular, for PE binaries). - Demangling (including non-Itanium demangling, e.g. Microsoft or Rust). - Disassembling (perf annotate). However, these are much less pressing; most people don't profile PE binaries, and perf has non-bfd paths for ELF. The same with demangling; the default _cxa_demangle path works fine for most users, and while bfd objdump can be slow on large binaries, it is possible to use --objdump=llvm-objdump to get the speed benefits. (It appears LLVM-based demangling is very simple, should we want that.) Tested with LLVM 14, 15, 16, 18 and 19. For some reason, LLVM 12 was not correctly detected using feature_check, and thus was not tested. Committer notes: Added the name and a __maybe_unused to address: 1 13.50 almalinux:8 : FAIL gcc version 8.5.0 20210514 (Red Hat 8.5.0-22) (GCC) util/srcline.c: In function 'dso__free_a2l': util/srcline.c:184:20: error: parameter name omitted void dso__free_a2l(struct dso *) ^~~~~~~~~~~~ make[3]: *** [/git/perf-6.11.0-rc3/tools/build/Makefile.build:158: util] Error 2 Signed-off-by: Steinar H. Gunderson Tested-by: Arnaldo Carvalho de Melo Cc: Ian Rogers Link: https://lore.kernel.org/r/20240803152008.2818485-1-sesse@google.com Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/llvm-c-helpers.cpp | 134 +++++++++++++++++++++++++++++++++++++ 1 file changed, 134 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 000000000000..3cc967ec6f28 --- /dev/null +++ b/tools/perf/util/llvm-c-helpers.cpp @@ -0,0 +1,134 @@ +// 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 +#pragma GCC diagnostic pop + +#include +#include +#include +extern "C" { +#include +} +#include "symbol_conf.h" +#include "llvm-c-helpers.h" + +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); + } +} -- cgit v1.2.3-70-g09d2