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charset="UTF-8" During DSO symbol loading in dso__load_sym_internal(), dso__demangle_sym() is called for every ELF symbol. Both rust_demangle_demangle() and java_demangle_sym() previously performed string searches or buffer allocations before checking whether the symbol name could possibly be a mangled Rust or Java symbol, adding unnecessary overhead on plain C symbols. Add fast-path prefix checks in dso__demangle_sym() before calling rust_demangle_demangle() (using strstarts() for '_ZN', 'ZN', '__ZN', '_R', 'R', or '__R', keeping demangle-rust-v0.c unmodified relative to upstream rustc-demangle) and in java_demangle_sym() (requiring 'L', ';', '(', and ')') to reject non-Rust and non-Java symbol names immediately. Using 'perf bench internals symbols': Before (perf binary): Average DSO load + sort: 7.348 msec (+- 0.069 msec) After (perf binary, -4.2%): Average DSO load + sort: 7.041 msec (+- 0.051 msec) Before (libLLVM.so.21.1): Average DSO load + sort: 81.196 msec (+- 0.780 msec) After (libLLVM.so.21.1, -3.2%): Average DSO load + sort: 78.599 msec (+- 0.857 msec) Signed-off-by: Ian Rogers --- tools/perf/util/demangle-java.c | 23 +++++++++++++++++++++-- tools/perf/util/symbol.c | 15 ++++++++++++++- 2 files changed, 35 insertions(+), 3 deletions(-) diff --git a/tools/perf/util/demangle-java.c b/tools/perf/util/demangle-java.c index c3cb327ed562..5625c4de39eb 100644 --- a/tools/perf/util/demangle-java.c +++ b/tools/perf/util/demangle-java.c @@ -158,14 +158,33 @@ char * java_demangle_sym(const char *str, int flags) { char *buf, *ptr; - const char *p; + const char *l, *semi, *open, *p; size_t len, l1 = 0; if (!str) return NULL; + /* + * OpenJDK JIT symbols have the form: + * [prefix]L;() + * where the return type (such as 'I' for int or 'V' for void) is at the + * end after ')'. In __demangle_java_sym(), the parser starts in + * MODE_PREFIX and only reaches MODE_TYPE (required when ')' is reached) + * via 'L' (MODE_CLASS) -> ';' (MODE_FUNC) -> '(' (MODE_TYPE). Verify + * those delimiters appear in order before allocating the output buffer. + */ + l = strchr(str, 'L'); + if (!l) + return NULL; + semi = strchr(l + 1, ';'); + if (!semi) + return NULL; + open = strchr(semi + 1, '('); + if (!open) + return NULL; + /* find start of return type */ - p = strrchr(str, ')'); + p = strrchr(open + 1, ')'); if (!p) return NULL; diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c index 0deda26181e0..cea8b9db8cd3 100644 --- a/tools/perf/util/symbol.c +++ b/tools/perf/util/symbol.c @@ -2732,7 +2732,20 @@ char *dso__demangle_sym(struct dso *dso, int kmodule, const char *elf_name) if (!want_demangle((dso && dso__kernel(dso)) || kmodule)) return demangled; - rust_demangle_demangle(elf_name, &rust_demangle); + /* + * Rust mangled symbols start with one of the prefixes checked by + * rust_demangle_legacy_demangle() ("_ZN", Windows dbghelp "ZN", or + * macOS "__ZN") or rust_demangle_v0_demangle() ("_R", Windows dbghelp + * "R", or macOS "__R") in demangle-rust-v0.c. Check the prefix here so + * we avoid calling rust_demangle_demangle() (which scans the entire + * symbol name with strstr() and strlen() for ThinLTO ".llvm." suffixes) + * on non-Rust symbols, while keeping demangle-rust-v0.c unmodified + * relative to upstream rustc-demangle. + */ + if (strstarts(elf_name, "_ZN") || strstarts(elf_name, "ZN") || + strstarts(elf_name, "__ZN") || strstarts(elf_name, "_R") || + strstarts(elf_name, "R") || strstarts(elf_name, "__R")) + rust_demangle_demangle(elf_name, &rust_demangle); if (rust_demangle_is_known(&rust_demangle)) { /* A rust mangled name. */ if (rust_demangle.mangled_len == 0) -- 2.56.1.703.gf848ed807c-goog