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Diffstat (limited to 'tools/perf/util/demangle-rust.c')
| -rw-r--r-- | tools/perf/util/demangle-rust.c | 270 |
1 files changed, 270 insertions, 0 deletions
diff --git a/tools/perf/util/demangle-rust.c b/tools/perf/util/demangle-rust.c new file mode 100644 index 000000000..423afbbd3 --- /dev/null +++ b/tools/perf/util/demangle-rust.c @@ -0,0 +1,270 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <string.h> +#include "util.h" +#include "debug.h" + +#include "demangle-rust.h" + +/* + * Mangled Rust symbols look like this: + * + * _$LT$std..sys..fd..FileDesc$u20$as$u20$core..ops..Drop$GT$::drop::hc68340e1baa4987a + * + * The original symbol is: + * + * <std::sys::fd::FileDesc as core::ops::Drop>::drop + * + * The last component of the path is a 64-bit hash in lowercase hex, prefixed + * with "h". Rust does not have a global namespace between crates, an illusion + * which Rust maintains by using the hash to distinguish things that would + * otherwise have the same symbol. + * + * Any path component not starting with a XID_Start character is prefixed with + * "_". + * + * The following escape sequences are used: + * + * "," => $C$ + * "@" => $SP$ + * "*" => $BP$ + * "&" => $RF$ + * "<" => $LT$ + * ">" => $GT$ + * "(" => $LP$ + * ")" => $RP$ + * " " => $u20$ + * "'" => $u27$ + * "[" => $u5b$ + * "]" => $u5d$ + * "~" => $u7e$ + * + * A double ".." means "::" and a single "." means "-". + * + * The only characters allowed in the mangled symbol are a-zA-Z0-9 and _.:$ + */ + +static const char *hash_prefix = "::h"; +static const size_t hash_prefix_len = 3; +static const size_t hash_len = 16; + +static bool is_prefixed_hash(const char *start); +static bool looks_like_rust(const char *sym, size_t len); +static bool unescape(const char **in, char **out, const char *seq, char value); + +/* + * INPUT: + * sym: symbol that has been through BFD-demangling + * + * This function looks for the following indicators: + * + * 1. The hash must consist of "h" followed by 16 lowercase hex digits. + * + * 2. As a sanity check, the hash must use between 5 and 15 of the 16 possible + * hex digits. This is true of 99.9998% of hashes so once in your life you + * may see a false negative. The point is to notice path components that + * could be Rust hashes but are probably not, like "haaaaaaaaaaaaaaaa". In + * this case a false positive (non-Rust symbol has an important path + * component removed because it looks like a Rust hash) is worse than a + * false negative (the rare Rust symbol is not demangled) so this sets the + * balance in favor of false negatives. + * + * 3. There must be no characters other than a-zA-Z0-9 and _.:$ + * + * 4. There must be no unrecognized $-sign sequences. + * + * 5. There must be no sequence of three or more dots in a row ("..."). + */ +bool +rust_is_mangled(const char *sym) +{ + size_t len, len_without_hash; + + if (!sym) + return false; + + len = strlen(sym); + if (len <= hash_prefix_len + hash_len) + /* Not long enough to contain "::h" + hash + something else */ + return false; + + len_without_hash = len - (hash_prefix_len + hash_len); + if (!is_prefixed_hash(sym + len_without_hash)) + return false; + + return looks_like_rust(sym, len_without_hash); +} + +/* + * A hash is the prefix "::h" followed by 16 lowercase hex digits. The hex + * digits must comprise between 5 and 15 (inclusive) distinct digits. + */ +static bool is_prefixed_hash(const char *str) +{ + const char *end; + bool seen[16]; + size_t i; + int count; + + if (strncmp(str, hash_prefix, hash_prefix_len)) + return false; + str += hash_prefix_len; + + memset(seen, false, sizeof(seen)); + for (end = str + hash_len; str < end; str++) + if (*str >= '0' && *str <= '9') + seen[*str - '0'] = true; + else if (*str >= 'a' && *str <= 'f') + seen[*str - 'a' + 10] = true; + else + return false; + + /* Count how many distinct digits seen */ + count = 0; + for (i = 0; i < 16; i++) + if (seen[i]) + count++; + + return count >= 5 && count <= 15; +} + +static bool looks_like_rust(const char *str, size_t len) +{ + const char *end = str + len; + + while (str < end) + switch (*str) { + case '$': + if (!strncmp(str, "$C$", 3)) + str += 3; + else if (!strncmp(str, "$SP$", 4) + || !strncmp(str, "$BP$", 4) + || !strncmp(str, "$RF$", 4) + || !strncmp(str, "$LT$", 4) + || !strncmp(str, "$GT$", 4) + || !strncmp(str, "$LP$", 4) + || !strncmp(str, "$RP$", 4)) + str += 4; + else if (!strncmp(str, "$u20$", 5) + || !strncmp(str, "$u27$", 5) + || !strncmp(str, "$u5b$", 5) + || !strncmp(str, "$u5d$", 5) + || !strncmp(str, "$u7e$", 5)) + str += 5; + else + return false; + break; + case '.': + /* Do not allow three or more consecutive dots */ + if (!strncmp(str, "...", 3)) + return false; + /* Fall through */ + case 'a' ... 'z': + case 'A' ... 'Z': + case '0' ... '9': + case '_': + case ':': + str++; + break; + default: + return false; + } + + return true; +} + +/* + * INPUT: + * sym: symbol for which rust_is_mangled(sym) returns true + * + * The input is demangled in-place because the mangled name is always longer + * than the demangled one. + */ +void +rust_demangle_sym(char *sym) +{ + const char *in; + char *out; + const char *end; + + if (!sym) + return; + + in = sym; + out = sym; + end = sym + strlen(sym) - (hash_prefix_len + hash_len); + + while (in < end) + switch (*in) { + case '$': + if (!(unescape(&in, &out, "$C$", ',') + || unescape(&in, &out, "$SP$", '@') + || unescape(&in, &out, "$BP$", '*') + || unescape(&in, &out, "$RF$", '&') + || unescape(&in, &out, "$LT$", '<') + || unescape(&in, &out, "$GT$", '>') + || unescape(&in, &out, "$LP$", '(') + || unescape(&in, &out, "$RP$", ')') + || unescape(&in, &out, "$u20$", ' ') + || unescape(&in, &out, "$u27$", '\'') + || unescape(&in, &out, "$u5b$", '[') + || unescape(&in, &out, "$u5d$", ']') + || unescape(&in, &out, "$u7e$", '~'))) { + pr_err("demangle-rust: unexpected escape sequence"); + goto done; + } + break; + case '_': + /* + * If this is the start of a path component and the next + * character is an escape sequence, ignore the + * underscore. The mangler inserts an underscore to make + * sure the path component begins with a XID_Start + * character. + */ + if ((in == sym || in[-1] == ':') && in[1] == '$') + in++; + else + *out++ = *in++; + break; + case '.': + if (in[1] == '.') { + /* ".." becomes "::" */ + *out++ = ':'; + *out++ = ':'; + in += 2; + } else { + /* "." becomes "-" */ + *out++ = '-'; + in++; + } + break; + case 'a' ... 'z': + case 'A' ... 'Z': + case '0' ... '9': + case ':': + *out++ = *in++; + break; + default: + pr_err("demangle-rust: unexpected character '%c' in symbol\n", + *in); + goto done; + } + +done: + *out = '\0'; +} + +static bool unescape(const char **in, char **out, const char *seq, char value) +{ + size_t len = strlen(seq); + + if (strncmp(*in, seq, len)) + return false; + + **out = value; + + *in += len; + *out += 1; + + return true; +} |