143 lines
3.7 KiB
TeX
143 lines
3.7 KiB
TeX
\subsection{Feature vs. Platform Checks}
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\begin{frame}
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\frametitle{Feature checks}
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\begin{center}
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\huge Probing the outside system\\for capabilities
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\end{center}
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\end{frame}
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% --------------------------------------------------------------------
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\begin{frame}
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\frametitle{What's a ``Feature''}
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Distinctive attribute which may have influence on the final system being built.\\
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\\
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Can be classified in 3 domains:
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\begin{itemize}
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\item Platform features\\
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{\info {library, symbols, functions, type size}}
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\item Compiler features\\
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{\info {variadic templates, constexpr, final, override}}
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\item System dictated features\\
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{\info {no-exceptions, no-rtti, no logging}}
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\end{itemize}
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\end{frame}
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% --------------------------------------------------------------------
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\begin{frame}[containsverbatim]
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\frametitle {Platform specific feature check}
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\textbf{Bad}
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\begin{codebox}{CMake}{}
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if(IOS OR ANDROID OR UNIX)
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target_compile_definitions(lua PRIVATE HAVE_POSIX_SPAWN)
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endif()
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\end{codebox}
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\textbf{Good}
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\begin{codebox}{CMake}{}
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check_symbol_exists("posix_spawn" "spawn.h" has_posix_spawn)
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if(has_posix_spawn)
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target_compile_definitions(lua PRIVATE HAVE_POSIX_SPAWN)
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endif()
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\end{codebox}
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\end{frame}
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% --------------------------------------------------------------------
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\begin{frame}[containsverbatim]
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\frametitle {Compiler specific feature checks}
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\textbf{Bad}
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\begin{codebox}[minted options={fontsize=\tiny}]{CMake}{}
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if(CMAKE_SYSTEM_NAME STREQUAL "QNX")
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target_compile_definitions(my-library
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PRIVATE -DBOOST_THREAD_DONT_USE_CHRONO)
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endif()
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\end{codebox}
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\textbf{Good}
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\begin{codebox}[minted options={fontsize=\tiny}]{CMake}{}
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# (incomplete example, checking for exception support is slightly harder)
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check_cxx_source_compile("
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int main() {
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#if !defined(__EXCEPTIONS)
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#error Exceptions not supported.
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#endif
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}" exceptions_supported)
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if(NOT exceptions_supported)
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target_compile_definitions(my-library
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PRIVATE -DBOOST_THREAD_DONT_USE_CHRONO)
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endif()
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\end{codebox}
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\end{frame}
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% --------------------------------------------------------------------
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\begin{frame}[containsverbatim]
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\frametitle {System dictated feature checks}
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\textbf{Bad}
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\begin{codebox}[minted options={fontsize=\scriptsize}]{CMake}{}
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find_package(Boost)
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if(Boost_FOUND)
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add_definition(ENABLE_FEATURE_X)
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endif()
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\end{codebox}
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\textbf {Good}
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\begin{codebox}[minted options={fontsize=\scriptsize}]{CMake}{}
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# In product config file
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set(ENABLE_FEATURE_X TRUE)
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# In project configuration
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if(ENABLE_FEATURE_X)
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find_package(Boost REQUIRED)
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add_definition(FEATURE_X_ENABLED)
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endif()
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\end{codebox}
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\end{frame}
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% --------------------------------------------------------------------
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\begin{frame}
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\frametitle{Functions for configure checks}
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CMake provides an API to check:
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\begin{itemize}
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\item Header existence: {\code{check\_include\_file()}}
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\item Library existence: {\code{check\_library\_exists()}}
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\item Symbol existence: {\code{check\_symbol\_exists()}}
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\item Supported type sizes: {\code{check\_type\_size()}}
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\end{itemize}
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CMake provides an API to write custom checks via:
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\begin{itemize}
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\item {\code{try\_compile()}}
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\item {\code{try\_run()}}
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\end{itemize}
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With {\code configure\_file} you can generate a header file
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enabling required code switches based on the checks.
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\end{frame}
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% --------------------------------------------------------------------
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\note{
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What is Platform check
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What is feature check
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CMAKE system introspection interface
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-What type of checks can be done with CMAKE
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https://cmake.org/Wiki/CMake:How\_To\_Write\_Platform\_Checks
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Pros and Cons
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}
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