* doc/extend.texi (Variable Attributes): Re-sort table and tidy.
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Richard Henderson
Richard Henderson
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2003-05-05 Richard Henderson <rth@redhat.com>
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* doc/extend.texi (Variable Attributes): Re-sort table and tidy.
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2003-05-05 David O'Brien <obrien@FreeBSD.org>
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* config/rs6000/sysv4.h (CPP_OS_FREEBSD_SPEC): Add __ELF__ to mirror
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@ -2367,15 +2367,6 @@ since it is known that the calling function loaded the correct value.
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Not all ELF targets support this attribute.
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@item tls_model ("@var{tls_model}")
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@cindex @code{tls_model} attribute
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The @code{tls_model} attribute sets thread-local storage model
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(@pxref{Thread-Local}) of a particular @code{__thread} variable,
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overriding @code{-ftls-model=} command line switch on a per-variable
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basis.
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The @var{tls_model} argument should be one of @code{global-dynamic},
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@code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
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@item regparm (@var{number})
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@cindex functions that are passed arguments in registers on the 386
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On the Intel 386, the @code{regparm} attribute causes the compiler to
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@ -2958,15 +2949,13 @@ It is an error to ask for the alignment of an incomplete type.
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The keyword @code{__attribute__} allows you to specify special
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attributes of variables or structure fields. This keyword is followed
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by an attribute specification inside double parentheses. Ten
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attributes are currently defined for variables: @code{aligned},
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@code{mode}, @code{nocommon}, @code{packed}, @code{section},
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@code{transparent_union}, @code{unused}, @code{deprecated},
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@code{vector_size}, and @code{weak}. Some other attributes are defined
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for variables on particular target systems. Other attributes are
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available for functions (@pxref{Function Attributes}) and for types
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(@pxref{Type Attributes}). Other front ends might define more
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attributes (@pxref{C++ Extensions,,Extensions to the C++ Language}).
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by an attribute specification inside double parentheses. Some
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attributes are currently defined generically for variables.
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Other attributes are defined for variables on particular target
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systems. Other attributes are available for functions
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(@pxref{Function Attributes}) and for types (@pxref{Type Attributes}).
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Other front ends might define more attributes
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(@pxref{C++ Extensions,,Extensions to the C++ Language}).
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You may also specify attributes with @samp{__} preceding and following
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each keyword. This allows you to use them in header files without
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@ -3034,6 +3023,40 @@ up to a maximum of 8 byte alignment, then specifying @code{aligned(16)}
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in an @code{__attribute__} will still only provide you with 8 byte
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alignment. See your linker documentation for further information.
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@item common
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@itemx nocommon
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@cindex @code{common} attribute
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@cindex @code{nocommon} attribute
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@opindex fcommon
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@opindex fno-common
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The @code{common} attribute requests GCC to place a variable in
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``common'' storage. The @code{nocommon} attribute requests the
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opposite -- to allocate space for it directly.
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These attributes override the default chosen by the
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@option{-fno-common} and @option{-fcommon} flags respectively.
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@item deprecated
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@cindex @code{deprecated} attribute
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The @code{deprecated} attribute results in a warning if the variable
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is used anywhere in the source file. This is useful when identifying
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variables that are expected to be removed in a future version of a
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program. The warning also includes the location of the declaration
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of the deprecated variable, to enable users to easily find further
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information about why the variable is deprecated, or what they should
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do instead. Note that the warnings only occurs for uses:
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@smallexample
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extern int old_var __attribute__ ((deprecated));
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extern int old_var;
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int new_fn () @{ return old_var; @}
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@end smallexample
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results in a warning on line 3 but not line 2.
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The @code{deprecated} attribute can also be used for functions and
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types (@pxref{Function Attributes}, @pxref{Type Attributes}.)
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@item mode (@var{mode})
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@cindex @code{mode} attribute
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This attribute specifies the data type for the declaration---whichever
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@ -3045,18 +3068,6 @@ indicate the mode corresponding to a one-byte integer, @samp{word} or
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@samp{__word__} for the mode of a one-word integer, and @samp{pointer}
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or @samp{__pointer__} for the mode used to represent pointers.
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@item nocommon
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@cindex @code{nocommon} attribute
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@opindex fno-common
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This attribute specifies requests GCC not to place a variable
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``common'' but instead to allocate space for it directly. If you
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specify the @option{-fno-common} flag, GCC will do this for all
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variables.
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Specifying the @code{nocommon} attribute for a variable provides an
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initialization of zeros. A variable may only be initialized in one
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source file.
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@item packed
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@cindex @code{packed} attribute
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The @code{packed} attribute specifies that a variable or structure field
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@ -3150,6 +3161,17 @@ linkers work. See @code{section} attribute for more information.
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The @code{shared} attribute is only available on Windows NT@.
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@item tls_model ("@var{tls_model}")
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@cindex @code{tls_model} attribute
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The @code{tls_model} attribute sets thread-local storage model
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(@pxref{Thread-Local}) of a particular @code{__thread} variable,
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overriding @code{-ftls-model=} command line switch on a per-variable
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basis.
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The @var{tls_model} argument should be one of @code{global-dynamic},
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@code{local-dynamic}, @code{initial-exec} or @code{local-exec}.
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Not all targets support this attribute.
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@item transparent_union
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This attribute, attached to a function parameter which is a union, means
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that the corresponding argument may have the type of any union member,
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@ -3163,26 +3185,6 @@ This attribute, attached to a variable, means that the variable is meant
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to be possibly unused. GCC will not produce a warning for this
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variable.
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@item deprecated
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The @code{deprecated} attribute results in a warning if the variable
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is used anywhere in the source file. This is useful when identifying
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variables that are expected to be removed in a future version of a
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program. The warning also includes the location of the declaration
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of the deprecated variable, to enable users to easily find further
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information about why the variable is deprecated, or what they should
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do instead. Note that the warnings only occurs for uses:
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@smallexample
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extern int old_var __attribute__ ((deprecated));
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extern int old_var;
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int new_fn () @{ return old_var; @}
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@end smallexample
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results in a warning on line 3 but not line 2.
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The @code{deprecated} attribute can also be used for functions and
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types (@pxref{Function Attributes}, @pxref{Type Attributes}.)
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@item vector_size (@var{bytes})
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This attribute specifies the vector size for the variable, measured in
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bytes. For example, the declaration:
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@ -3214,7 +3216,13 @@ the @code{int}.
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@item weak
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The @code{weak} attribute is described in @xref{Function Attributes}.
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@end table
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@subsection M32R/D Variable Attributes
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One attribute is currently defined for the M32R/D.
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@table @code
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@item model (@var{model-name})
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@cindex variable addressability on the M32R/D
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Use this attribute on the M32R/D to set the addressability of an object.
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@ -3227,16 +3235,18 @@ addresses can be loaded with the @code{ld24} instruction).
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Medium and large model objects may live anywhere in the 32-bit address space
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(the compiler will generate @code{seth/add3} instructions to load their
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addresses).
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@end table
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@subsection i386 Variable Attributes
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Two attributes are currently defined for i386 configurations:
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@code{ms_struct} and @code{gcc_struct}
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@table @code
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@item ms_struct
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@itemx gcc_struct
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@cindex @code{ms_struct}
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@cindex @code{gcc_struct}
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@cindex @code{ms_struct} attribute
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@cindex @code{gcc_struct} attribute
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If @code{packed} is used on a structure, or if bit-fields are used
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it may be that the Microsoft ABI packs them differently
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@ -3247,13 +3257,8 @@ either format.
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Currently @option{-m[no-]ms-bitfields} is provided for the Windows X86
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compilers to match the native Microsoft compiler.
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@end table
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To specify multiple attributes, separate them by commas within the
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double parentheses: for example, @samp{__attribute__ ((aligned (16),
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packed))}.
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@node Type Attributes
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@section Specifying Attributes of Types
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@cindex attribute of types
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