The aligned type attribute
With the aligned type attribute,
you can override the default alignment mode to specify a minimum alignment
value, expressed as a number of bytes, for a structure, 
classes
, union, enumeration,
or other user-defined type created in a typedef declaration.
The aligned attribute is typically used to increase
the alignment of any variables declared of the type to which the attribute
applies.
The alignment_factor is the number of bytes, specified as a constant expression that evaluates to a positive power of 2. If you omit the alignment factor (and its enclosing parentheses), the compiler automatically uses 16 bytes. You can specify a value up to a maximum 268435456 bytes. If you specify an alignment factor greater than the maximum, the compiler issues an error message and the compilation fails.aligned type attribute syntax >>-__attribute__------------------------------------------------> >--((--+-aligned-----+--+------------------------+--))--------->< '-__aligned__-' '-(--alignment_factor--)-'
The alignment value that you specify is applied to all instances of the type. Also, the alignment value applies to the variable as a whole; if the variable is an aggregate, the alignment value applies to the aggregate as a whole, not to the individual members of the aggregate.
Example
In all of the
following examples, the aligned attribute is applied
to the structure type A. Because a is
declared as a variable of type A, it also
receives the alignment specification, as any other instances
declared of type A.
struct __attribute__((__aligned__(8))) A {};
struct __attribute__((__aligned__(8))) A {} a;
typedef struct __attribute__((__aligned__(8))) A {} a;
