From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-oi2-f43.google.com (mail-oi2-f43.google.com [74.125.231.235]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 61ADD511E6E for ; Tue, 22 Sep 2026 07:19:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.231.235 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790061579; cv=none; b=lH8KdfcXDLve8nvQZ/Qfw9zfZCBZAK6ohNiLNDAuv6fCqxFhX4RtdB0tih7xYjnJWr8uWeKQMmg4Rfjw7MdnWOZJSNvnTrUU+jPQORISEtISGH8g/nG0XLUH30WNikGiDFLIYVNIqfm/5fj/HCWza8bg+0toXCFCp8Y/S6Tdw2E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790061579; c=relaxed/simple; bh=9+xXUpbmhRcfphY9oEfLvGM9tZCICquHCMD3yOi8tIk=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=WS2dmW+IztKy11jtSLCGAgiyZEu+tsIM4WEj92+YiD2ogI23GszKcu/3MnRBYXhWu62wqUXGuNL1luPhsn0kehmXOoJKAZwQeuT4NC4yZuyv1URnag2haMovt2LyFNVlpanljmZBlVlEp5MtIXy4evgjqfxsPgRVQwF4mDTXb4Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=BAtIGZnG; arc=none smtp.client-ip=74.125.231.235 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="BAtIGZnG" Received: by mail-oi2-f43.google.com with SMTP id 46e09a7af769-7f4f0d1779dso3330110a34.2 for ; Tue, 22 Sep 2026 00:19:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1790061569; x=1790666369; darn=vger.kernel.org; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :content-type:mime-version:subject:date:from:from:to:cc:subject:date :message-id:reply-to:content-type; bh=U9x3FI5E4GbuVg0Jfsu35zQ33gdkfajY2nImRMYOyJE=; b=BAtIGZnGN6Wph4it868B9tZapl14iGOUMvokwOo3HUHwT4wBh/0wqCDN8VV/kI6bPK DzfcvFygSfaz9YbbYH0pOWrIvPh8NfHafL5MezzROsNErXMN9xxYqjqF5POSS4aqWoMd 5NX8vRqcQqBi//89WI/xuhMd72OWGnPT5/mZVGMvvMzoDcCCbBJzEWsA1POyk5Rk85pi YCMreAOmt3wb42nGGI5PXoDeuXhAHfzAKPk7zogVCxYaD35JqyB3nGzSM92ZwY3rskGi Y/RMUH64uQH1ip/sFLfgG/DtyWHXRuVJYWDmIXG5e6iAsg2niKOaqh5cPekv5j/jWrCq cihQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1790061569; x=1790666369; h=cc:to:in-reply-to:references:message-id:content-transfer-encoding :content-type:mime-version:subject:date:from:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=U9x3FI5E4GbuVg0Jfsu35zQ33gdkfajY2nImRMYOyJE=; b=hghYbeiqNAulu2PDdxCokHpei0x0CRjz1I3y0f32HgYco+atzmFlY5PmEtaiyPLUmw yCID2CjU2qVJxpgWXs/opf8hX/qwxlFp1vHyhp73KTALFl4yanSo1JOLkw36R65QLU80 biUJ1OwgCc7T/1dBAQevFUDXlB4AqyzkEqbd0QlyRXKD457UN6mCKv8qUjioHdK+EVjI L9e7q1dVAkuwbxUU3+lZdYiiG3xb4ProEvDYlW2Nv7JkzJqRW7/r5LrxjWx5Ig8UXzlb MZnfaVSCILZr1UUzohkm1NdrGkLj5Rj5pv+e4jIWkycD3vpbv6F0Cs3khFRSzd+AXkXc xCLg== X-Forwarded-Encrypted: i=1; AKwUvBy0XJkRdpOUIepuk/tlBoqcWVXbIpfhortlauEU+vyeI2t+q0q6JtjSGqF8WHw79h9D3IUW/sS7x42gnGs=@vger.kernel.org X-Gm-Message-State: AFuF++nPafUZAwz+i7oqWTiif+kRWRnvOSpOnLaoB00vckbEtNmfCm3C ev+2/eZtlmeIYEUEz2zBXzvFCa4k5pKJLNdqHhEb54lkSyQtb2v/o+Iv X-Gm-Gg: AYBFou13N2HPKS45IVLtcP/kw/dr4hJolAVjAe7BNR0k2KT6BozIMZd4XMEd5M8d2YR tML8OdF9gckZK/KiXNmtdbAa99pIlzGEr0pZh6629HtYRqif/53QD0aU7UVnok6XFYoF7EkWDim zkrJFzeR3KSZDPiex/Hwc4lr01Ygv5/es6DatqPLKc6piDJa7wjlgjNpGWlCUwLC96OEJhEsk7w 4mbfKCYd7yQCXQUepVcZo9CLEvgu6Hr9mtD5ZaeOgv3pNRdzxTZ50e7Vnj37E5gvzMrSzzAyNqf xkuu03Z028Hw2eVW037iF++MczIcWPiAc4K9f5IbNqW0BLOo3Uxrfbm46Ibf7BDbuiFOYyO0xiY JzJqFZiMcjr1jIx5KCzdNvk1RxsPuGcqrEXqXhqNMcG0SXJSR5kjCfeR2lFzj0j/G6Ivt4UVQJo Vb7FoWDw5C4DF+fRSwmfZlEY78T/r0aHTvIo4+dyO0p65HjCwjuTtiXArmytEG7NJTndNXmRHsi N/R1tQHkF3jjSe9jNGc+lxs8yS5xYYi4E2YlH7/zBa+sP+VKoL6vKTrSKnYPODlQS1Ug1+R68lR 3txKkWKPmWN2cKh63H4= X-Received: by 2002:a05:6830:81ca:b0:80b:6c70:94b9 with SMTP id 46e09a7af769-80de27dc7cfmr15537606a34.19.1790061569165; Tue, 22 Sep 2026 00:19:29 -0700 (PDT) Received: from [100.82.231.29] (c-98-38-17-99.hsd1.co.comcast.net. [98.38.17.99]) by smtp.googlemail.com with ESMTPSA id 46e09a7af769-814e598483esm1116801a34.5.2026.09.22.00.19.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Sep 2026 00:19:28 -0700 (PDT) From: Jim Cromie Date: Tue, 22 Sep 2026 01:19:21 -0600 Subject: [PATCH v2 3/3] kallsyms: Match compressed tokens on the fly during binary search Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260922-ksyms-tune-v2-3-a333ee31eac7@gmail.com> References: <20260922-ksyms-tune-v2-0-a333ee31eac7@gmail.com> In-Reply-To: <20260922-ksyms-tune-v2-0-a333ee31eac7@gmail.com> To: Andrew Morton Cc: Lorenzo Stoakes , Kees Cook , David Laight , Masahiro Yamada , linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, bpf@vger.kernel.org, Jim Cromie X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=ed25519-sha256; t=1790061561; l=6187; i=jim.cromie@gmail.com; s=20260203; h=from:subject:message-id; bh=9+xXUpbmhRcfphY9oEfLvGM9tZCICquHCMD3yOi8tIk=; b=zvOk3ZkgBsIKOndl6sO4Rqw248xKhWqXl2uhZas4Z5pbHJ3c+gNrOlSTb0rUNyBL4je9U9P4V sF+gitZnIB5CO1l8uvrKFK/4s0k6FN9UBAVmfs1iON3kx3I1T7uaQ5A X-Developer-Key: i=jim.cromie@gmail.com; a=ed25519; pk=C6E5ODlPQo7ZBynATXH9wg7K6HxP0pIXyf4s38Qw0XE= kallsyms_lookup_names() runs a binary search across kallsyms_names[], a packed array of ~130k encoded kernel symbols. For each of the ~17 comparisons in the search, it currently decompresses the candidate symbol into a temporary buffer on the stack before calling strcmp(). Comparing raw tokens directly in compressed space is impossible. The BPE token table assigns values by frequency, not alphabetical order (e.g. token 0x05 might expand to "zebra" while 0x42 expands to "apple"), so comparing raw token values scrambles lexicographical order. However, full string expansion is equally wasteful: roughly 16 of the 17 binary search steps fail within the first two characters. Introduce kallsyms_strcmp_symbol() to compare ASCII queries against compressed tokens on the fly. It walks kallsyms_token_index and kallsyms_token_table incrementally, matching characters directly and bailing out on the first character mismatch without expanding subsequent tokens. This optimization: 0. Avoids decompressing non-matching tokens, short-circuiting ~94% of binary search character expansions without adding any tables in .rodata. 1. Drops the 512-byte namebuf buffer from the kernel stack in kallsyms_lookup_names(). 2. Leaves sequential address ordering and kallsyms_expand_symbol() streaming invariants intact for /proc/kallsyms and table walks. Signed-off-by: Jim Cromie --- kernel/kallsyms.c | 97 ++++++++++++++++++++++++++++++++++--------------------- 1 file changed, 61 insertions(+), 36 deletions(-) diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index 862a6b773ac5..4a04d63e4b7d 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -37,6 +37,21 @@ #include "kallsyms_internal.h" +/* + * Get the compressed symbol length and data pointer. + */ +static inline const u8 *get_symbol_data(unsigned int off, unsigned int *len) +{ + const u8 *p = &kallsyms_names[off]; + unsigned int l = *p++; + + if (unlikely(l & 0x80)) + l = (l & 0x7F) | (*p++ << 7); + *len = l; + + return p; +} + /* * Expand a compressed symbol data into the resulting uncompressed string, * if uncompressed string is too long (>= maxlen), it will be truncated, @@ -45,28 +60,12 @@ static unsigned int kallsyms_expand_symbol(unsigned int off, char *result, size_t maxlen) { - int len, skipped_first = 0; + int skipped_first = 0; const char *tptr; - const u8 *data; + unsigned int len; + const u8 *data = get_symbol_data(off, &len); - /* Get the compressed symbol length from the first symbol byte. */ - data = &kallsyms_names[off]; - len = *data; - data++; - off++; - - /* If MSB is 1, it is a "big" symbol, so needs an additional byte. */ - if ((len & 0x80) != 0) { - len = (len & 0x7F) | (*data << 7); - data++; - off++; - } - - /* - * Update the offset to return the offset for the next symbol on - * the compressed stream. - */ - off += len; + off = (data - kallsyms_names) + len; /* * For every byte on the compressed symbol data, copy the table @@ -94,7 +93,7 @@ static unsigned int kallsyms_expand_symbol(unsigned int off, if (maxlen) *result = '\0'; - /* Return to offset to the next symbol. */ + /* Return offset to the next symbol. */ return off; } @@ -104,16 +103,46 @@ static unsigned int kallsyms_expand_symbol(unsigned int off, */ static char kallsyms_get_symbol_type(unsigned int off) { - /* - * Get just the first code, look it up in the token table, - * and return the first char from this token. If MSB of length - * is 1, it is a "big" symbol, so needs an additional byte. - */ - if (kallsyms_names[off] & 0x80) - off++; - return kallsyms_token_table[kallsyms_token_index[kallsyms_names[off + 1]]]; + unsigned int len; + const u8 *data = get_symbol_data(off, &len); + + return kallsyms_token_table[kallsyms_token_index[*data]]; } +/* + * Compare an uncompressed ASCII string against a compressed symbol table entry. + * Returns negative if name < sym, positive if name > sym, 0 if equal. + * Exits immediately on the first mismatched character without decompressing + * the rest of the symbol name. + */ +static int kallsyms_strcmp_symbol(unsigned int off, const char *name) +{ + int skipped_first = 0; + const char *tptr; + unsigned int len; + const u8 *data = get_symbol_data(off, &len); + + while (len) { + tptr = &kallsyms_token_table[kallsyms_token_index[*data]]; + data++; + len--; + + while (*tptr) { + if (skipped_first) { + int diff = (unsigned char)*name - (unsigned char)*tptr; + + if (diff != 0) + return diff; + name++; + } else { + skipped_first = 1; + } + tptr++; + } + } + + return (unsigned char)*name - '\0'; +} /* * Find the offset on the compressed stream given an index in the @@ -261,7 +290,6 @@ static int kallsyms_lookup_names(const char *name, int ret; int low, mid, high; unsigned int seq, off; - char namebuf[KSYM_NAME_LEN]; low = 0; high = kallsyms_num_syms - 1; @@ -271,8 +299,7 @@ static int kallsyms_lookup_names(const char *name, mid = low + (high - low) / 2; seq = get_symbol_seq(mid); off = get_symbol_offset(seq); - kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); - ret = strcmp(name, namebuf); + ret = kallsyms_strcmp_symbol(off, name); if (ret > 0) low = mid + 1; else if (ret < 0) @@ -290,8 +317,7 @@ static int kallsyms_lookup_names(const char *name, while (low) { seq = get_symbol_seq(low - 1); off = get_symbol_offset(seq); - kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); - if (strcmp(name, namebuf)) + if (kallsyms_strcmp_symbol(off, name) != 0) break; low--; } @@ -302,8 +328,7 @@ static int kallsyms_lookup_names(const char *name, while (high < kallsyms_num_syms - 1) { seq = get_symbol_seq(high + 1); off = get_symbol_offset(seq); - kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf)); - if (strcmp(name, namebuf)) + if (kallsyms_strcmp_symbol(off, name) != 0) break; high++; } -- 2.55.0