From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailtransmit05.runbox.com (mailtransmit05.runbox.com [185.226.149.38]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E1DFF3C8728; Sun, 18 Oct 2026 15:53:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.226.149.38 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792338800; cv=none; b=S9ap7iHGt796uusWZel/vmyFVDD/749YG7nAmuzoAC/qI57Y+mGgXJ1u3ubxBv+eEYYyxQGkp/erIx9bHdmYLLR0lSDNIgZXi+CMH2mLwyP+egLW2GSq/26P1IhY1uf1A5ilHY3+EAL6J1MX6kGg6BftQ4EgDSsItQ+sgMWtEgs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792338800; c=relaxed/simple; bh=9w7RU5zcujV+KSe7J6OW/8YyFKXnIOzIBtcy+k5du9A=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=qlADSlJ5N9r8vW0RoNhOE1+QyzqKX2Rg0urvGfkWARRp/dhR8gGDyY3IUxPLLuRrSac1sUQHRIZRIlH2XTWGHkfsKokwCqKwc5yzKFg5IGKML1uflvH9FudFA6xzQRD3sYdcoDoXy9iR+nR6TESMUfW9E9VeMkORt5VT0awwsik= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=runbox.com; dkim=pass (2048-bit key) header.d=runbox.com header.i=@runbox.com header.b=d4t9NWle; arc=none smtp.client-ip=185.226.149.38 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=runbox.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=runbox.com header.i=@runbox.com header.b="d4t9NWle" Received: from mailtransmit02.runbox ([10.9.9.162] helo=aibo.runbox.com) by mailtransmit05.runbox.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1xITC3-001KAn-Mw; Sun, 18 Oct 2026 17:53:03 +0200 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=runbox.com; s=selector1; h=Content-Transfer-Encoding:MIME-Version:References:In-Reply-To :Message-Id:Date:Subject:Cc:To:From; bh=fP6dHKs+XEgtmnRzI+NAxjgMH9T3XFvRmKv/GSHjTzw=; b=d4t9NWle8a1oDEN3hbdinreGJ8 a8AtbWfwtf4lhU7ZQR/g9r91kYaQrEngNWcX08oZZexwRTg5dKcczIHjqB/YJZG4PSH8RKkDBLCeL KA1idlyteJJ6+c2xjhs5wJlzZNpL6kTDKFzW6Pnitm1PpKHw9QaN2l6FbqatQ1rtnyGKmOvoVrSW7 xmQlhgZbudrnPCEckQJQ/HxCueeWSAt42Zjz/ILPnCqoXLwqF8rKX28dqNYEYi7ArkM8aLC7ZYKpp Pbwk7F5Eg7L90t+kk5Yiov+aKvCkKi8H7NBrK6nAivc3OheNiXhsTV73bBVI8kvc0DUWKct1W5AKm XHOeGn+Q==; Received: from [10.9.9.74] (helo=submission03.runbox) by mailtransmit02.runbox with esmtp (Exim 4.86_2) (envelope-from ) id 1xITBy-0001ol-BV; Sun, 18 Oct 2026 17:52:58 +0200 Received: by submission03.runbox with esmtpsa [Authenticated ID (1493616)] (TLS1.2:ECDHE_SECP256R1__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.95) id 1xITBg-004q3U-3P; Sun, 18 Oct 2026 17:52:40 +0200 From: David Laight To: Andrew Morton , Petr Mladek , Kees Cook , David Laight , linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, bpf@vger.kernel.org, Jim Cromie , Lorenzo Stoakes Cc: Luis Chamberlain , Andrey Grodzovsky , Steven Rostedt Subject: [PATCH v2 next 05/15] kallsyms: Match compressed tokens on the fly during binary search Date: Sun, 18 Oct 2026 16:51:56 +0100 Message-Id: <20261018155206.132411-6-david.laight.linux@gmail.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20261018155206.132411-1-david.laight.linux@gmail.com> References: <20261018155206.132411-1-david.laight.linux@gmail.com> Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Jim Cromie kallsyms_lookup_names() runs a binary search across ~184k tokenized (compressed) 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 tokenized symbols 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. Even sorting the token table alphabetically wouldn't help; "bpf_" and "bpf_foo_" do not *have* a determinative sorting order, because the suffixes following those tokens would matter. However, full string expansion at every step is equally wasteful: of the ~17 strcmps in the binary search, only the last needs to check all N chars in both strings, earlier steps will know +/- outcome at char 0,1,2..N-1. However, full string expansion at every step is equally wasteful: of the ~17 strcmp()s in the binary search, only the final matching step needs to test all characters. Earlier non-matching steps diverge at the first differing character (0..N-1), but the baseline expands every candidate symbol to the stack unconditionally, before comparing. So we introduce kallsyms_strcmp_symbol() to compare ASCII search_name against tokenized symbols on the fly. Like strcmp, it tests the strings char by char, but when it hits a token in the symbol-string, it continues the char-test against that token-string, which is in kallsyms_token_table[]. It returns +- on 1st mismatch. Measured across all ~184k symbols via CONFIG_KALLSYMS_SELFTEST, this shaves ~530 ns (~14%) off average kallsyms_lookup_name() latency (from ~3810 ns to ~3280 ns on the default 256:1 baseline) and drops the 512-byte namebuf buffer stack-alloc in kallsyms_lookup_names(). Signed-off-by: Jim Cromie Signed-off-by: David Laight --- kernel/kallsyms.c | 94 +++++++++++++++++++++++++++++------------------ 1 file changed, 59 insertions(+), 35 deletions(-) diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c index aec2f06858af..d18d78e626db 100644 --- a/kernel/kallsyms.c +++ b/kernel/kallsyms.c @@ -34,6 +34,21 @@ #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, @@ -42,28 +57,12 @@ 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 @@ -101,14 +100,43 @@ 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) +{ + const char *tptr; + unsigned int len; + const u8 *data = get_symbol_data(off, &len); + + tptr = &kallsyms_token_table[kallsyms_token_index[*data++]] + 1; + while (*tptr) { + int diff = (unsigned char)*name++ - (unsigned char)*tptr++; + + if (diff) + return diff; + } + + while (--len) { + tptr = &kallsyms_token_table[kallsyms_token_index[*data++]]; + do { + int diff = (unsigned char)*name++ - (unsigned char)*tptr++; + + if (diff) + return diff; + } while (*tptr); + } + + return (unsigned char)*name; } @@ -174,7 +202,6 @@ 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; @@ -183,8 +210,7 @@ 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) @@ -200,8 +226,7 @@ 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--; } @@ -212,8 +237,7 @@ 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++; } -- 2.39.5