From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 032A5C7EE25 for ; Wed, 7 Jun 2023 20:29:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233589AbjFGU3Z (ORCPT ); Wed, 7 Jun 2023 16:29:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55682 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233583AbjFGU3V (ORCPT ); Wed, 7 Jun 2023 16:29:21 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 504C7269D for ; Wed, 7 Jun 2023 13:29:07 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id A77AB644C7 for ; Wed, 7 Jun 2023 20:28:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DE8C0C4339E; Wed, 7 Jun 2023 20:28:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686169733; bh=eY1UqwYJntMLMU5Yd8lkw/zWfSR41OHe1x/9kSmW+Ek=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ApBq1xCZHN18wc0R9zdT9eYGRLFkA6Xtg9RKeBK1uqlfn1dqJN+WMxfBH91SyGYTU /vFDACsUiC8E8iX1AIZIDOc37VngXOCJ/B0e8EDXAZlbApb038tasCxdrsE+XidvPP wuljKsHEZbxxrepFeDqdWN70kGasU4E9lB1jqWrzTzQHU/DS5/loxvZSwGFZyeJpct OBgimt/NtihYGQ6rJXJ4USE3mQJxPqtV2LLh7apiRo2yB8AMnQ2ZuEEDsrI9oyvWZW noxfeEw4wDNkjFqtvkdLS0EcvMSmYJXUIJPVouAPjvUgtrflsL0RQQO3WfGdHZKUqT PRmKof92hqkFw== From: Conor Dooley To: palmer@dabbelt.com Cc: conor@kernel.org, Conor Dooley , Paul Walmsley , Andrew Jones , Sunil V L , Yangyu Chen , Rob Herring , Krzysztof Kozlowski , devicetree@vger.kernel.org, linux-riscv@lists.infradead.org Subject: [PATCH v3 4/7] RISC-V: rework comments in ISA string parser Date: Wed, 7 Jun 2023 21:28:28 +0100 Message-Id: <20230607-headpiece-tannery-83ed5cc4856a@spud> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230607-audacity-overhaul-82bb867a825f@spud> References: <20230607-audacity-overhaul-82bb867a825f@spud> MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4612; i=conor.dooley@microchip.com; h=from:subject:message-id; bh=pRBb9rN0x8kEbAvR9LC8Ni1TdOFEl8xAcaZ/+5Mew2g=; b=owGbwMvMwCFWscWwfUFT0iXG02pJDCkNLzKrH83bnrv7k1D3pvfXf7RpsX4parjaJSAX6fKFS bRs4RrvjlIWBjEOBlkxRZbE230tUuv/uOxw7nkLM4eVCWQIAxenAExkaycjw15Wta0lkdNa3hw6 6c02eRH7ooSZby/tLf9ZX2t168zRu8KMDPs8Aq+taBd6dN7yyJLFgVFSqrp9833L92+Q4i6e2n5 mAyMA X-Developer-Key: i=conor.dooley@microchip.com; a=openpgp; fpr=F9ECA03CF54F12CD01F1655722E2C55B37CF380C Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org From: Conor Dooley I have found these comments to not be at all helpful whenever I look at the parser. Further, the comments in the default case (single letter parser) are not quite right either. Group the comments into a larger one at the start of each case, that attempts to explain things at a higher level. Reviewed-by: Andrew Jones Signed-off-by: Conor Dooley --- arch/riscv/kernel/cpufeature.c | 70 ++++++++++++++++++++++++++++------ 1 file changed, 59 insertions(+), 11 deletions(-) diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index c3851c8cfa9c..7dd4589e79a4 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -164,7 +164,7 @@ void __init riscv_fill_hwcap(void) switch (*ext) { case 's': - /** + /* * Workaround for invalid single-letter 's' & 'u'(QEMU). * No need to set the bit in riscv_isa as 's' & 'u' are * not valid ISA extensions. It works until multi-letter @@ -181,53 +181,101 @@ void __init riscv_fill_hwcap(void) case 'X': case 'z': case 'Z': + /* + * Before attempting to parse the extension itself, we find its end. + * As multi-letter extensions must be split from other multi-letter + * extensions with an "_", the end of a multi-letter extension will + * either be the null character or the "_" at the start of the next + * multi-letter extension. + * + * Next, as the extensions version is currently ignored, we + * eliminate that portion. This is done by parsing backwards from + * the end of the extension, removing any numbers. This may be a + * major or minor number however, so the process is repeated if a + * minor number was found. + * + * ext_end is intended to represent the first character *after* the + * name portion of an extension, but will be decremented to the last + * character itself while eliminating the extensions version number. + * A simple re-increment solves this problem. + */ ext_long = true; - /* Multi-letter extension must be delimited */ for (; *isa && *isa != '_'; ++isa) if (unlikely(!isalnum(*isa))) ext_err = true; - /* Parse backwards */ + ext_end = isa; if (unlikely(ext_err)) break; + if (!isdigit(ext_end[-1])) break; - /* Skip the minor version */ + while (isdigit(*--ext_end)) ; - if (tolower(ext_end[0]) != 'p' - || !isdigit(ext_end[-1])) { - /* Advance it to offset the pre-decrement */ + + if (tolower(ext_end[0]) != 'p' || !isdigit(ext_end[-1])) { ++ext_end; break; } - /* Skip the major version */ + while (isdigit(*--ext_end)) ; + ++ext_end; break; default: + /* + * Things are a little easier for single-letter extensions, as they + * are parsed forwards. + * + * After checking that our starting position is valid, we need to + * ensure that, when isa was incremented at the start of the loop, + * that it arrived at the start of the next extension. + * + * If we are already on a non-digit, there is nothing to do. Either + * we have a multi-letter extension's _, or the start of an + * extension. + * + * Otherwise we have found the current extension's major version + * number. Parse past it, and a subsequent p/minor version number + * if present. The `p` extension must not appear immediately after + * a number, so there is no fear of missing it. + * + */ if (unlikely(!isalpha(*ext))) { ext_err = true; break; } - /* Find next extension */ + if (!isdigit(*isa)) break; - /* Skip the minor version */ + while (isdigit(*++isa)) ; + if (tolower(*isa) != 'p') break; + if (!isdigit(*++isa)) { --isa; break; } - /* Skip the major version */ + while (isdigit(*++isa)) ; + break; } + + /* + * The parser expects that at the start of an iteration isa points to the + * character before the start of the next extension. This will not be the + * case if we have just parsed a single-letter extension and the next + * extension is not a multi-letter extension prefixed with an "_". It is + * also not the case at the end of the string, where it will point to the + * terminating null character. + */ if (*isa != '_') --isa; -- 2.39.2