From: Ivan Zakharyaschev <imz@altlinux.org> To: ALT Linux Team development discussions <devel@lists.altlinux.org> Cc: darktemplar@altlinux.org Subject: Re: [devel] re APT patch with impossible error on "Can't allocate an item of size zero" Date: Thu, 13 Feb 2020 05:43:42 +0300 (MSK) Message-ID: <alpine.LFD.2.20.2002130540580.6363@imap.altlinux.org> (raw) In-Reply-To: <alpine.LFD.2.20.2002130502010.6363@imap.altlinux.org> [-- Attachment #1: Type: text/plain, Size: 4248 bytes --] On Thu, 13 Feb 2020, Ivan Zakharyaschev wrote: > В ветке sisyphus_one_more_time в > git://git.altlinux.org/people/darktemplar/packages/apt.git в коммите > > commit f53c1af17e2997ff6d2e23139bc61f5d5c82a547 > есть такой hunk касательно DynamicMMap::RawAllocate(): > Во-вторых, я подумал, что это такой класс ошибок, который не возникает > в run-time из-за плохих данных или отказа ОС (например, выделить > память или прочитать файл) -- т.е. не что-то заранее непредсказуемое > для программиста и поэтому требующее специальной обработки в run-time. > > Если програмист написал всё так, как он хотел, то он не передаст > неправильный аргумент (0) в функцию. (Да и понятно, что в реальном > коде APT это не ожидается: там обычно этот аргумент заполняется > константой sizeof(...).) > > Я бы предложил такие требования (имеющие характер спецификации того, > что программист задумал реализовать) оформлять просто с помощью > assert. Отразил это в коммите у себя в ветке, которая должна будет конвергироваться с sisyphus_one_more_time commit ab3d7b79f9a582d4b01efad5e9fdf1a0455f735f Author: Ivan Zakharyaschev <imz@altlinux.org> Date: Wed Jan 29 21:40:53 2020 +0300 DynamicMMap::RawAllocate(): assert that a zero-size item is never allocated Actually, we are always called with sizeof(...) compile-time non-zero constant as the argument: The only invocation of Allocate() that can be found with: git grep -nH -Ee '(^|[^[:alpha:]])Allocate\(' is the following function: std::experimental::optional<map_ptrloc> pkgCacheGenerator::AllocateInMap(unsigned long size) {/*{{{*/ void *oldMap = Map.Data(); const auto index = Map.Allocate(size); if (index) ReMap(oldMap, Map.Data()); return index; } Now, look how AllocateInMap() is used: git --no-pager grep -nH -Ee '(^|[^[:alpha:]])AllocateInMap\(' apt/apt-pkg/pkgcachegen.cc:167:std::experimental::optional<map_ptrloc> pkgCacheGenerator::AllocateInMap(unsigned long size) {/*{{{*/ apt/apt-pkg/pkgcachegen.cc:449: const auto Package = AllocateInMap(sizeof(pkgCache::Package)); apt/apt-pkg/pkgcachegen.cc:502: const auto VerFile = AllocateInMap(sizeof(pkgCache::VerFile)); apt/apt-pkg/pkgcachegen.cc:533: const auto Version = AllocateInMap(sizeof(pkgCache::Version)); apt/apt-pkg/pkgcachegen.cc:561: const auto Dependency = Owner->AllocateInMap(sizeof(pkgCache::Dependency)); apt/apt-pkg/pkgcachegen.cc:639: const auto Provides = Owner->AllocateInMap(sizeof(pkgCache::Provides)); apt/apt-pkg/pkgcachegen.cc:686: const auto idxFile = AllocateInMap(sizeof(*CurrentFile)); apt/apt-pkg/pkgcachegen.cc:744: const auto Item = AllocateInMap(sizeof(pkgCache::StringItem)); apt/apt-pkg/pkgcachegen.h:45: std::experimental::optional<map_ptrloc> AllocateInMap(unsigned long size); The argument is always a sizeof(...) constant expression. Picked the idea of this single change from: commit 6d5e6a689d07de8feef2cbecb24bc42d5994861b Author: Aleksei Nikiforov <darktemplar@altlinux.org> Date: Tue Jun 11 14:53:47 2019 +0300 apt-pkg/pkgcachegen.{cc,h} changes make the used MMap moveable (and therefore dynamic resizeable) by applying (some) mad pointer magic Ported from Apt from Debian but rewritten with an assert statement. diff --git a/apt/apt-pkg/contrib/mmap.cc b/apt/apt-pkg/contrib/mmap.cc index 77aad3656..e0373365a 100644 --- a/apt/apt-pkg/contrib/mmap.cc +++ b/apt/apt-pkg/contrib/mmap.cc @@ -37,6 +37,7 @@ #include <unistd.h> #include <fcntl.h> #include <cstring> +#include <cassert> /*}}}*/ // MMap::MMap - Constructor /*{{{*/ @@ -226,6 +227,10 @@ std::experimental::optional<unsigned long> DynamicMMap::RawAllocate(unsigned lon size in the file. */ std::experimental::optional<unsigned long> DynamicMMap::Allocate(unsigned long ItemSize) { + assert(ItemSize != 0); /* Actually, we are always called with sizeof(...) + compile-time non-zero constant as the argument. + */ + // Look for a matching pool entry Pool *I; Pool *Empty = 0;
next prev parent reply other threads:[~2020-02-13 2:43 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-02-13 2:08 Ivan Zakharyaschev 2020-02-13 2:43 ` Ivan Zakharyaschev [this message] 2020-02-13 12:59 ` Aleksei Nikiforov 2020-02-13 14:10 ` Ivan Zakharyaschev 2020-02-13 17:05 ` Ivan Zakharyaschev 2020-02-17 8:41 ` Ivan Zakharyaschev 2020-02-17 14:05 ` Andrey Savchenko 2020-02-17 17:48 ` Ivan Zakharyaschev 2020-02-17 21:35 ` Dmitry V. Levin 2020-02-17 21:58 ` Ivan Zakharyaschev 2020-02-13 14:51 ` Ivan Zakharyaschev
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