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During a patch discussion, Linus brought up the option of changing the C standard version from gnu89 to gnu99, which allows using variable declaration inside of a for() loop. While the C99, C11 and later standards introduce many other features, most of these are already available in gnu89 as GNU extensions as well. An earlier attempt to do this when gcc-5 started defaulting to -std=gnu11 failed because at the time that caused warnings about designated initializers with older compilers. Now that gcc-5.1 is the minimum compiler version used for building kernels, that is no longer a concern. Similarly, the behavior of 'inline' functions changes between gnu89 using gnu_inline behavior and gnu11 using standard c99+ behavior, but this was taken care of by defining 'inline' to include __attribute__((gnu_inline)) in order to allow building with clang a while ago. Nathan Chancellor reported a new -Wdeclaration-after-statement warning that appears in a system header on arm, this still needs a workaround. The differences between gnu99, gnu11, gnu1x and gnu17 are fairly minimal and mainly impact warnings at the -Wpedantic level that the kernel never enables. Between these, gnu11 is the newest version that is supported by all supported compiler versions, though it is only the default on gcc-5, while all other supported versions of gcc or clang default to gnu1x/gnu17. Link: https://lore.kernel.org/lkml/CAHk-=wiyCH7xeHcmiFJ-YgXUy2Jaj7pnkdKpcovt8fYbVFW3TA@mail.gmail.com/ Link: https://github.com/ClangBuiltLinux/linux/issues/1603 Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: Marco Elver <elver@google.com> Acked-by: Jani Nikula <jani.nikula@intel.com> Acked-by: David Sterba <dsterba@suse.com> Tested-by: Sedat Dilek <sedat.dilek@gmail.com> Reviewed-by: Alex Shi <alexs@kernel.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Miguel Ojeda <ojeda@kernel.org> Signed-off-by: Arnd Bergmann <arnd@arndb.de> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
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.. SPDX-License-Identifier: GPL-2.0
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.. include:: ../disclaimer-zh_TW.rst
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:Original: :ref:`Documentation/process/programming-language.rst <programming_language>`
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:Translator: Alex Shi <alex.shi@linux.alibaba.com>
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Hu Haowen <src.res@email.cn>
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.. _tw_programming_language:
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程序設計語言
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============
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內核是用C語言 :ref:`c-language <tw_c-language>` 編寫的。更準確地說，內核通常是用 :ref:`gcc <tw_gcc>`
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在 ``-std=gnu11`` :ref:`gcc-c-dialect-options <tw_gcc-c-dialect-options>` 下編譯的：ISO C11的 GNU 方言
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這種方言包含對語言 :ref:`gnu-extensions <tw_gnu-extensions>` 的許多擴展，當然，它們許多都在內核中使用。
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對於一些體系結構，有一些使用 :ref:`clang <tw_clang>` 和 :ref:`icc <tw_icc>` 編譯內核
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的支持，儘管在編寫此文檔時還沒有完成，仍需要第三方補丁。
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屬性
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----
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在整個內核中使用的一個常見擴展是屬性（attributes） :ref:`gcc-attribute-syntax <tw_gcc-attribute-syntax>`
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屬性允許將實現定義的語義引入語言實體（如變量、函數或類型），而無需對語言進行
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重大的語法更改（例如添加新關鍵字） :ref:`n2049 <tw_n2049>`
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在某些情況下，屬性是可選的（即不支持這些屬性的編譯器仍然應該生成正確的代碼，
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即使其速度較慢或執行的編譯時檢查/診斷次數不夠）
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內核定義了僞關鍵字（例如， ``pure`` ），而不是直接使用GNU屬性語法（例如,
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``__attribute__((__pure__))`` ），以檢測可以使用哪些關鍵字和/或縮短代碼, 具體
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請參閱 ``include/linux/compiler_attributes.h``
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.. _tw_c-language:
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c-language
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http://www.open-std.org/jtc1/sc22/wg14/www/standards
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.. _tw_gcc:
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gcc
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https://gcc.gnu.org
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.. _tw_clang:
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clang
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https://clang.llvm.org
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.. _tw_icc:
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icc
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https://software.intel.com/en-us/c-compilers
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.. _tw_gcc-c-dialect-options:
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c-dialect-options
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https://gcc.gnu.org/onlinedocs/gcc/C-Dialect-Options.html
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.. _tw_gnu-extensions:
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gnu-extensions
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https://gcc.gnu.org/onlinedocs/gcc/C-Extensions.html
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.. _tw_gcc-attribute-syntax:
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gcc-attribute-syntax
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https://gcc.gnu.org/onlinedocs/gcc/Attribute-Syntax.html
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.. _tw_n2049:
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n2049
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http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2049.pdf
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