// SPDX-License-Identifier: GPL-2.0
#include <string.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;
}
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