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c3b7b56dd0
Document the way `__attribute__((__constructor__))` and `__attribute__((__destructor__))` must be used in BIND9 libraries in order to avoid unexpected behaviors with other third-party libraries.
64 lines
2 KiB
C
64 lines
2 KiB
C
/*
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* Copyright (C) Internet Systems Consortium, Inc. ("ISC")
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*
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* SPDX-License-Identifier: MPL-2.0
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*
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* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, you can obtain one at https://mozilla.org/MPL/2.0/.
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*
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* See the COPYRIGHT file distributed with this work for additional
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* information regarding copyright ownership.
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*/
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/*
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* BIND9 constructor/destructor README
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* -----------------------------------
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*
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* A function tagged with `__attribute__((__destructor__))` is called right
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* after `main()` returns (or `exit()` is called; see `man atexit` for more
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* details). However is a valid assumption _only_ if the function is defined
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* inside the binary.
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*
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* If the function is defined as part of a shared library, it will
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* be called only when the library is unloaded by the OS linker. There is no
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* way to control the order in which two destructor functions "A" and "B" are
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* called if they are defined in separate libraries, because it depends
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* on the order in which the OS linker unloads the libraries.
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*
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* As a consequence, all contructor/destructor functions of BIND9 must be
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* defined in `lib/<lib>/include/<lib>/lib.h` header and such header must be
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* included in each binaries (in each C file defining `main()`) and must not be
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* included in any library.
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*
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* Otherwise, there might be interference. For example, LSAN which could run
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* before the BIND9 destructor functions have cleaned up remaining non-root
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* memory.
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*
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* The order of the calls between the BIND9 constructors/destructors is enforced
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* by a reference counter in the `<lib>__lib_{initialize,shutdown}` functions.
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*/
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#pragma once
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#include <isc/util.h>
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void
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isc__lib_initialize(void);
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void
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isc__lib_shutdown(void);
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void
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isc_lib_initialize(void) __attribute__((__constructor__));
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void
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isc_lib_shutdown(void) __attribute__((__destructor__));
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void
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isc_lib_initialize(void) {
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isc__lib_initialize();
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}
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void
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isc_lib_shutdown(void) {
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isc__lib_shutdown();
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}
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