mirror of https://github.com/qpdf/qpdf.git
135 lines
4.5 KiB
C
135 lines
4.5 KiB
C
/* Copyright (c) 2005-2022 Jay Berkenbilt
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*
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* This file is part of qpdf.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* Versions of qpdf prior to version 7 were released under the terms
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* of version 2.0 of the Artistic License. At your option, you may
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* continue to consider qpdf to be licensed under those terms. Please
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* see the manual for additional information.
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*/
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#ifndef QPDF_DLL_HH
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#define QPDF_DLL_HH
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/* The first version of qpdf to include the version constants is 10.6.0. */
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#define QPDF_MAJOR_VERSION 11
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#define QPDF_MINOR_VERSION 3
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#define QPDF_PATCH_VERSION 0
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#define QPDF_VERSION "11.3.0"
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/*
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* This file defines symbols that control the which functions,
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* classes, and methods are exposed to the public ABI (application
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* binary interface). See below for a detailed explanation.
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*/
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#if defined _WIN32 || defined __CYGWIN__
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# ifdef libqpdf_EXPORTS
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# define QPDF_DLL __declspec(dllexport)
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# else
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# define QPDF_DLL
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# endif
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# define QPDF_DLL_PRIVATE
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#elif defined __GNUC__
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# define QPDF_DLL __attribute__((visibility("default")))
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# define QPDF_DLL_PRIVATE __attribute__((visibility("hidden")))
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#else
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# define QPDF_DLL
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# define QPDF_DLL_PRIVATE
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#endif
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#ifdef __GNUC__
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# define QPDF_DLL_CLASS QPDF_DLL
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#else
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# define QPDF_DLL_CLASS
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#endif
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/*
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Here's what's happening. See also https://gcc.gnu.org/wiki/Visibility
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for a more in-depth discussion.
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* Everything in the public ABI must be exported. Things not in the
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public ABI should not be exported.
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* A class's runtime type information is need if the class is going to
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be used as an exception, inherited from, or tested with
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dynamic_class. To do these things across a shared object boundary,
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runtime type information must be exported.
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* On Windows:
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* For a symbol (function, method, etc.) to be exported into the
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public ABI, it must be explicitly marked for export.
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* If you mark a class for export, all symbols in the class,
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including private methods, are exported into the DLL, and there is
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no way to exclude something from export.
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* A class's run-time type information is made available based on the
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presence of a compiler flag (with MSVC), which is always on for
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qpdf builds.
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* Marking classes for export should be done only when *building* the
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DLL, not when *using* the DLL.
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* It is possible to mark symbols for import for DLL users, but it is
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not necessary, and doing it right is complex in our case of being
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multi-platform and building both static and shared libraries that
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use the same headers, so we don't bother.
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* If we don't export base classes with mingw, the vtables don't end
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up in the DLL.
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* On Linux (and other similar systems):
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* Common compilers such as gcc and clang export all symbols into the
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public ABI by default. The qpdf build overrides this by using
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"visibility=hidden", which makes it behave more like Windows in
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that things have to be explicitly exported to appear in the public
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ABI.
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* As with Windows, marking a class for export causes everything in
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the class, including private methods, the be exported. However,
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unlike in Windows:
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* It is possible to explicitly mark symbols as private
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* The only way to get the runtime type and vtable information into
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the ABI is to mark the class as exported.
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* It is harmless and sometimes necessary to include the visibility
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marks when using the library as well as when building it. In
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particular, clang on MacOS requires the visibility marks to
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match in both cases.
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What does this mean:
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* On Windows, we never have to export a class, and while there is no
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way to "unexport" something, we also have no need to do it.
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* On non-Windows, we have to export some classes, and when we do, we
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have to "unexport" some of their parts.
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* We only use the libqpdf_EXPORTS as a conditional for defining the
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symbols for Windows builds.
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To achieve this, we use QPDF_DLL_CLASS to export classes, QPDF_DLL to
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export methods, and QPDF_DLL_PRIVATE to unexport private methods in
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exported classes.
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*/
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#endif /* QPDF_DLL_HH */
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