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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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.. include:: ../disclaimer-zh_CN.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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.. _cn_programming_language:
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程序设计语言
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============
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内核是用C语言 :ref:`c-language <cn_c-language>` 编写的。更准确地说，内核通常是用 :ref:`gcc <cn_gcc>`
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在 ``-std=gnu11`` :ref:`gcc-c-dialect-options <cn_gcc-c-dialect-options>` 下编译的：ISO C11的 GNU 方言
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这种方言包含对语言 :ref:`gnu-extensions <cn_gnu-extensions>` 的许多扩展，当然，它们许多都在内核中使用。
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对于一些体系结构，有一些使用 :ref:`clang <cn_clang>` 和 :ref:`icc <cn_icc>` 编译内核
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的支持，尽管在编写此文档时还没有完成，仍需要第三方补丁。
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属性
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----
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在整个内核中使用的一个常见扩展是属性（attributes） :ref:`gcc-attribute-syntax <cn_gcc-attribute-syntax>`
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属性允许将实现定义的语义引入语言实体（如变量、函数或类型），而无需对语言进行
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重大的语法更改（例如添加新关键字） :ref:`n2049 <cn_n2049>`
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在某些情况下，属性是可选的（即不支持这些属性的编译器仍然应该生成正确的代码，
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即使其速度较慢或执行的编译时检查/诊断次数不够）
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内核定义了伪关键字（例如， ``pure`` ），而不是直接使用GNU属性语法（例如,
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``__attribute__((__pure__))`` ），以检测可以使用哪些关键字和/或缩短代码, 具体
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请参阅 ``include/linux/compiler_attributes.h``
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.. _cn_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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.. _cn_gcc:
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gcc
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https://gcc.gnu.org
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.. _cn_clang:
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clang
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https://clang.llvm.org
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.. _cn_icc:
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icc
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https://software.intel.com/en-us/c-compilers
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.. _cn_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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.. _cn_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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.. _cn_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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.. _cn_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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