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59 lines
2.0 KiB
Plaintext
59 lines
2.0 KiB
Plaintext
@node stdalign.h
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@section @file{stdalign.h}
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POSIX specification:@* Not in POSIX yet, but we expect it will be.
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ISO C11 (latest free draft
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@url{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf})
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sections 6.5.3.4, 6.7.5, 7.15.
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C++11 (latest free draft
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@url{http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf})
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section 18.10.
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Gnulib module: stdalign
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Portability problems fixed by Gnulib:
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@itemize
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@item
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This header file is missing on most circa-2011 platforms.
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@item
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Clang 3.0's @code{<stdalign.h>} does not define @code{alignof}/@code{_Alignof}.
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@item
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The @code{alignof} and @code{_Alignof} macros return too large values for
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the types @code{double} and @code{long long} in GCC 4.7.0.
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@end itemize
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Portability problems not fixed by Gnulib:
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@itemize
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@item
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@code{_Alignas} and @code{alignas} are not always supported;
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on platforms lacking support, the
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macro @code{__alignas_is_defined} is not defined.
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Supported compilers include GCC, IBM C, Sun C 5.11 and later,
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and MSVC 7.0 and later.
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@item
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Some compilers do not support alignment via
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@code{alignas}/@code{_Alignas} of @code{auto} variables (i.e.,
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variables on the stack). They diagnose and ignore the alignment: Sun
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C 5.11.
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@item
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Some linkers do not support operands of @code{_Alignas}/@code{alignas}
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that are greater than 8: mingw.
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@item
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Some compilers require the operand of @code{_Alignas}/@code{alignas}
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to be a single integer constant, not an expression: MSVC 7.0 through
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at least 10.0.
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@item
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The Sun C 5.11 compiler sometimes mishandles the alignment of multiple
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external variables that are declared close together with
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@code{_Alignas}/@code{alignas}. This compiler bug causes the Gnulib
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module @code{stdalign-tests} to fail. The Sun Studio Developer Bug
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Report Review Team assigned the internal review ID 2125432 (dated
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2011-11-01) to this issue.
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@item
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@code{<stdalign.h>} must be #included before @code{_Alignas} and
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@code{_Alignof} can be used.
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@item
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You cannot assume that @code{_Alignas} and @code{_Alignof} are reserved words;
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they might be macros.
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@end itemize
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