| GNU Compiler Collection (GCC) Internals: Type Layout |
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These macros define the sizes and other characteristics of the standard basic data types used in programs being compiled. Unlike the macros in the previous section, these apply to specific features of C and related languages, rather than to fundamental aspects of storage layout.
A C expression for the size in bits of the type int on the
target machine. If you don’t define this, the default is one word.
A C expression for the size in bits of the type short on the
target machine. If you don’t define this, the default is half a word.
(If this would be less than one storage unit, it is rounded up to one
unit.)
A C expression for the size in bits of the type long on the
target machine. If you don’t define this, the default is one word.
On some machines, the size used for the Ada equivalent of the type
long by a native Ada compiler differs from that used by C. In
that situation, define this macro to be a C expression to be used for
the size of that type. If you don’t define this, the default is the
value of LONG_TYPE_SIZE.
A C expression for the size in bits of the type long long on the
target machine. If you don’t define this, the default is two
words. If you want to support GNU Ada on your machine, the value of this
macro must be at least 64.
A C expression for the size in bits of the type char on the
target machine. If you don’t define this, the default is
BITS_PER_UNIT.
A C expression for the size in bits of the C++ type bool and
C99 type _Bool on the target machine. If you don’t define
this, and you probably shouldn’t, the default is CHAR_TYPE_SIZE.
A C expression for the size in bits of the type float on the
target machine. If you don’t define this, the default is one word.
A C expression for the size in bits of the type double on the
target machine. If you don’t define this, the default is two
words.
A C expression for the size in bits of the type long double on
the target machine. If you don’t define this, the default is two
words.
A C expression for the size in bits of the type short _Fract on
the target machine. If you don’t define this, the default is
BITS_PER_UNIT.
A C expression for the size in bits of the type _Fract on
the target machine. If you don’t define this, the default is
BITS_PER_UNIT * 2.
A C expression for the size in bits of the type long _Fract on
the target machine. If you don’t define this, the default is
BITS_PER_UNIT * 4.
A C expression for the size in bits of the type long long _Fract on
the target machine. If you don’t define this, the default is
BITS_PER_UNIT * 8.
A C expression for the size in bits of the type short _Accum on
the target machine. If you don’t define this, the default is
BITS_PER_UNIT * 2.
A C expression for the size in bits of the type _Accum on
the target machine. If you don’t define this, the default is
BITS_PER_UNIT * 4.
A C expression for the size in bits of the type long _Accum on
the target machine. If you don’t define this, the default is
BITS_PER_UNIT * 8.
A C expression for the size in bits of the type long long _Accum on
the target machine. If you don’t define this, the default is
BITS_PER_UNIT * 16.
This macro corresponds to the TARGET_LIBFUNC_GNU_PREFIX target
hook and should be defined if that hook is overriden to be true. It
causes function names in libgcc to be changed to use a __gnu_
prefix for their name rather than the default __. A port which
uses this macro should also arrange to use t-gnu-prefix in
the libgcc config.host.
A C expression for the size in bits of the widest floating-point format
supported by the hardware. If you define this macro, you must specify a
value less than or equal to the value of LONG_DOUBLE_TYPE_SIZE.
If you do not define this macro, the value of LONG_DOUBLE_TYPE_SIZE
is the default.
An expression whose value is 1 or 0, according to whether the type
char should be signed or unsigned by default. The user can
always override this default with the options -fsigned-char
and -funsigned-char.
This target hook should return true if the compiler should give an
enum type only as many bytes as it takes to represent the range
of possible values of that type. It should return false if all
enum types should be allocated like int.
The default is to return false.
A C expression for a string describing the name of the data type to use
for size values. The typedef name size_t is defined using the
contents of the string.
The string can contain more than one keyword. If so, separate them with
spaces, and write first any length keyword, then unsigned if
appropriate, and finally int. The string must exactly match one
of the data type names defined in the function
c_common_nodes_and_builtins in the file c-family/c-common.c.
You may not omit int or change the order—that would cause the
compiler to crash on startup.
If you don’t define this macro, the default is "long unsigned
int".
GCC defines internal types (sizetype, ssizetype,
bitsizetype and sbitsizetype) for expressions
dealing with size. This macro is a C expression for a string describing
the name of the data type from which the precision of sizetype
is extracted.
The string has the same restrictions as SIZE_TYPE string.
If you don’t define this macro, the default is SIZE_TYPE.
A C expression for a string describing the name of the data type to use
for the result of subtracting two pointers. The typedef name
ptrdiff_t is defined using the contents of the string. See
SIZE_TYPE above for more information.
If you don’t define this macro, the default is "long int".
A C expression for a string describing the name of the data type to use
for wide characters. The typedef name wchar_t is defined using
the contents of the string. See SIZE_TYPE above for more
information.
If you don’t define this macro, the default is "int".
A C expression for the size in bits of the data type for wide
characters. This is used in cpp, which cannot make use of
WCHAR_TYPE.
A C expression for a string describing the name of the data type to
use for wide characters passed to printf and returned from
getwc. The typedef name wint_t is defined using the
contents of the string. See SIZE_TYPE above for more
information.
If you don’t define this macro, the default is "unsigned int".
A C expression for a string describing the name of the data type that
can represent any value of any standard or extended signed integer type.
The typedef name intmax_t is defined using the contents of the
string. See SIZE_TYPE above for more information.
If you don’t define this macro, the default is the first of
"int", "long int", or "long long int" that has as
much precision as long long int.
A C expression for a string describing the name of the data type that
can represent any value of any standard or extended unsigned integer
type. The typedef name uintmax_t is defined using the contents
of the string. See SIZE_TYPE above for more information.
If you don’t define this macro, the default is the first of
"unsigned int", "long unsigned int", or "long long
unsigned int" that has as much precision as long long unsigned
int.
C expressions for the standard types sig_atomic_t,
int8_t, int16_t, int32_t, int64_t,
uint8_t, uint16_t, uint32_t, uint64_t,
int_least8_t, int_least16_t, int_least32_t,
int_least64_t, uint_least8_t, uint_least16_t,
uint_least32_t, uint_least64_t, int_fast8_t,
int_fast16_t, int_fast32_t, int_fast64_t,
uint_fast8_t, uint_fast16_t, uint_fast32_t,
uint_fast64_t, intptr_t, and uintptr_t. See
SIZE_TYPE above for more information.
If any of these macros evaluates to a null pointer, the corresponding
type is not supported; if GCC is configured to provide
<stdint.h> in such a case, the header provided may not conform
to C99, depending on the type in question. The defaults for all of
these macros are null pointers.
The C++ compiler represents a pointer-to-member-function with a struct that looks like:
struct {
union {
void (*fn)();
ptrdiff_t vtable_index;
};
ptrdiff_t delta;
};
The C++ compiler must use one bit to indicate whether the function that
will be called through a pointer-to-member-function is virtual.
Normally, we assume that the low-order bit of a function pointer must
always be zero. Then, by ensuring that the vtable_index is odd, we can
distinguish which variant of the union is in use. But, on some
platforms function pointers can be odd, and so this doesn’t work. In
that case, we use the low-order bit of the delta field, and shift
the remainder of the delta field to the left.
GCC will automatically make the right selection about where to store
this bit using the FUNCTION_BOUNDARY setting for your platform.
However, some platforms such as ARM/Thumb have FUNCTION_BOUNDARY
set such that functions always start at even addresses, but the lowest
bit of pointers to functions indicate whether the function at that
address is in ARM or Thumb mode. If this is the case of your
architecture, you should define this macro to
ptrmemfunc_vbit_in_delta.
In general, you should not have to define this macro. On architectures
in which function addresses are always even, according to
FUNCTION_BOUNDARY, GCC will automatically define this macro to
ptrmemfunc_vbit_in_pfn.
Normally, the C++ compiler uses function pointers in vtables. This macro allows the target to change to use “function descriptors” instead. Function descriptors are found on targets for whom a function pointer is actually a small data structure. Normally the data structure consists of the actual code address plus a data pointer to which the function’s data is relative.
If vtables are used, the value of this macro should be the number of words that the function descriptor occupies.
By default, the vtable entries are void pointers, the so the alignment is the same as pointer alignment. The value of this macro specifies the alignment of the vtable entry in bits. It should be defined only when special alignment is necessary. */
There are a few non-descriptor entries in the vtable at offsets below
zero. If these entries must be padded (say, to preserve the alignment
specified by TARGET_VTABLE_ENTRY_ALIGN), set this to the number
of words in each data entry.
Next: Registers, Previous: Storage Layout, Up: Target Macros [Contents][Index]