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1// SPDX-License-Identifier: GPL-2.02#include <string.h>3#include "debug.h"4 5#include "demangle-rust.h"6 7/*8 * Mangled Rust symbols look like this:9 *10 * _$LT$std..sys..fd..FileDesc$u20$as$u20$core..ops..Drop$GT$::drop::hc68340e1baa4987a11 *12 * The original symbol is:13 *14 * <std::sys::fd::FileDesc as core::ops::Drop>::drop15 *16 * The last component of the path is a 64-bit hash in lowercase hex, prefixed17 * with "h". Rust does not have a global namespace between crates, an illusion18 * which Rust maintains by using the hash to distinguish things that would19 * otherwise have the same symbol.20 *21 * Any path component not starting with a XID_Start character is prefixed with22 * "_".23 *24 * The following escape sequences are used:25 *26 * "," => $C$27 * "@" => $SP$28 * "*" => $BP$29 * "&" => $RF$30 * "<" => $LT$31 * ">" => $GT$32 * "(" => $LP$33 * ")" => $RP$34 * " " => $u20$35 * "'" => $u27$36 * "[" => $u5b$37 * "]" => $u5d$38 * "~" => $u7e$39 *40 * A double ".." means "::" and a single "." means "-".41 *42 * The only characters allowed in the mangled symbol are a-zA-Z0-9 and _.:$43 */44 45static const char *hash_prefix = "::h";46static const size_t hash_prefix_len = 3;47static const size_t hash_len = 16;48 49static bool is_prefixed_hash(const char *start);50static bool looks_like_rust(const char *sym, size_t len);51static bool unescape(const char **in, char **out, const char *seq, char value);52 53/*54 * INPUT:55 * sym: symbol that has been through BFD-demangling56 *57 * This function looks for the following indicators:58 *59 * 1. The hash must consist of "h" followed by 16 lowercase hex digits.60 *61 * 2. As a sanity check, the hash must use between 5 and 15 of the 16 possible62 * hex digits. This is true of 99.9998% of hashes so once in your life you63 * may see a false negative. The point is to notice path components that64 * could be Rust hashes but are probably not, like "haaaaaaaaaaaaaaaa". In65 * this case a false positive (non-Rust symbol has an important path66 * component removed because it looks like a Rust hash) is worse than a67 * false negative (the rare Rust symbol is not demangled) so this sets the68 * balance in favor of false negatives.69 *70 * 3. There must be no characters other than a-zA-Z0-9 and _.:$71 *72 * 4. There must be no unrecognized $-sign sequences.73 *74 * 5. There must be no sequence of three or more dots in a row ("...").75 */76bool77rust_is_mangled(const char *sym)78{79 size_t len, len_without_hash;80 81 if (!sym)82 return false;83 84 len = strlen(sym);85 if (len <= hash_prefix_len + hash_len)86 /* Not long enough to contain "::h" + hash + something else */87 return false;88 89 len_without_hash = len - (hash_prefix_len + hash_len);90 if (!is_prefixed_hash(sym + len_without_hash))91 return false;92 93 return looks_like_rust(sym, len_without_hash);94}95 96/*97 * A hash is the prefix "::h" followed by 16 lowercase hex digits. The hex98 * digits must comprise between 5 and 15 (inclusive) distinct digits.99 */100static bool is_prefixed_hash(const char *str)101{102 const char *end;103 bool seen[16];104 size_t i;105 int count;106 107 if (strncmp(str, hash_prefix, hash_prefix_len))108 return false;109 str += hash_prefix_len;110 111 memset(seen, false, sizeof(seen));112 for (end = str + hash_len; str < end; str++)113 if (*str >= '0' && *str <= '9')114 seen[*str - '0'] = true;115 else if (*str >= 'a' && *str <= 'f')116 seen[*str - 'a' + 10] = true;117 else118 return false;119 120 /* Count how many distinct digits seen */121 count = 0;122 for (i = 0; i < 16; i++)123 if (seen[i])124 count++;125 126 return count >= 5 && count <= 15;127}128 129static bool looks_like_rust(const char *str, size_t len)130{131 const char *end = str + len;132 133 while (str < end)134 switch (*str) {135 case '$':136 if (!strncmp(str, "$C$", 3))137 str += 3;138 else if (!strncmp(str, "$SP$", 4)139 || !strncmp(str, "$BP$", 4)140 || !strncmp(str, "$RF$", 4)141 || !strncmp(str, "$LT$", 4)142 || !strncmp(str, "$GT$", 4)143 || !strncmp(str, "$LP$", 4)144 || !strncmp(str, "$RP$", 4))145 str += 4;146 else if (!strncmp(str, "$u20$", 5)147 || !strncmp(str, "$u27$", 5)148 || !strncmp(str, "$u5b$", 5)149 || !strncmp(str, "$u5d$", 5)150 || !strncmp(str, "$u7e$", 5))151 str += 5;152 else153 return false;154 break;155 case '.':156 /* Do not allow three or more consecutive dots */157 if (!strncmp(str, "...", 3))158 return false;159 /* Fall through */160 case 'a' ... 'z':161 case 'A' ... 'Z':162 case '0' ... '9':163 case '_':164 case ':':165 str++;166 break;167 default:168 return false;169 }170 171 return true;172}173 174/*175 * INPUT:176 * sym: symbol for which rust_is_mangled(sym) returns true177 *178 * The input is demangled in-place because the mangled name is always longer179 * than the demangled one.180 */181void182rust_demangle_sym(char *sym)183{184 const char *in;185 char *out;186 const char *end;187 188 if (!sym)189 return;190 191 in = sym;192 out = sym;193 end = sym + strlen(sym) - (hash_prefix_len + hash_len);194 195 while (in < end)196 switch (*in) {197 case '$':198 if (!(unescape(&in, &out, "$C$", ',')199 || unescape(&in, &out, "$SP$", '@')200 || unescape(&in, &out, "$BP$", '*')201 || unescape(&in, &out, "$RF$", '&')202 || unescape(&in, &out, "$LT$", '<')203 || unescape(&in, &out, "$GT$", '>')204 || unescape(&in, &out, "$LP$", '(')205 || unescape(&in, &out, "$RP$", ')')206 || unescape(&in, &out, "$u20$", ' ')207 || unescape(&in, &out, "$u27$", '\'')208 || unescape(&in, &out, "$u5b$", '[')209 || unescape(&in, &out, "$u5d$", ']')210 || unescape(&in, &out, "$u7e$", '~'))) {211 pr_err("demangle-rust: unexpected escape sequence");212 goto done;213 }214 break;215 case '_':216 /*217 * If this is the start of a path component and the next218 * character is an escape sequence, ignore the219 * underscore. The mangler inserts an underscore to make220 * sure the path component begins with a XID_Start221 * character.222 */223 if ((in == sym || in[-1] == ':') && in[1] == '$')224 in++;225 else226 *out++ = *in++;227 break;228 case '.':229 if (in[1] == '.') {230 /* ".." becomes "::" */231 *out++ = ':';232 *out++ = ':';233 in += 2;234 } else {235 /* "." becomes "-" */236 *out++ = '-';237 in++;238 }239 break;240 case 'a' ... 'z':241 case 'A' ... 'Z':242 case '0' ... '9':243 case ':':244 *out++ = *in++;245 break;246 default:247 pr_err("demangle-rust: unexpected character '%c' in symbol\n",248 *in);249 goto done;250 }251 252done:253 *out = '\0';254}255 256static bool unescape(const char **in, char **out, const char *seq, char value)257{258 size_t len = strlen(seq);259 260 if (strncmp(*in, seq, len))261 return false;262 263 **out = value;264 265 *in += len;266 *out += 1;267 268 return true;269}270