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    kbuild: compile-test exported headers to ensure they are self-contained · d6fc9fcb
    Masahiro Yamada 提交于
    Multiple people have suggested compile-testing UAPI headers to ensure
    they can be really included from user-space. "make headers_check" is
    obviously not enough to catch bugs, and we often leak unresolved
    references to user-space.
    
    Use the new header-test-y syntax to implement it. Please note exported
    headers are compile-tested with a completely different set of compiler
    flags. The header search path is set to $(objtree)/usr/include since
    exported headers should not include unexported ones.
    
    We use -std=gnu89 for the kernel space since the kernel code highly
    depends on GNU extensions. On the other hand, UAPI headers should be
    written in more standardized C, so they are compiled with -std=c90.
    This will emit errors if C++ style comments, the keyword 'inline', etc.
    are used. Please use C style comments (/* ... */), '__inline__', etc.
    in UAPI headers.
    
    There is additional compiler requirement to enable this test because
    many of UAPI headers include <stdlib.h>, <sys/ioctl.h>, <sys/time.h>,
    etc. directly or indirectly. You cannot use kernel.org pre-built
    toolchains [1] since they lack <stdlib.h>.
    
    I reused CONFIG_CC_CAN_LINK to check the system header availability.
    The intention is slightly different, but a compiler that can link
    userspace programs provide system headers.
    
    For now, a lot of headers need to be excluded because they cannot
    be compiled standalone, but this is a good start point.
    
    [1] https://mirrors.edge.kernel.org/pub/tools/crosstool/index.htmlSigned-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
    Reviewed-by: NSam Ravnborg <sam@ravnborg.org>
    d6fc9fcb
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