"andrew wiggin" <end3er@xxxxxxxxx> writes:
> struct _s1 {
> unsigned char e1;
> unsigned char e2;
> };
>
> struct _s2 {
> void e1;
> struct _s2 e2[2];
> void e3;
> };
This code doesn't compile. For discussing issues like this it helps
to see the exact code.
> The result is that with no packing attribute, the line "struct _s2
> e2[2];" will be interpreted as ".align 4 / .byte / .byte .align 4 /
> .byte / .byte" however there is absolutely no reason why this
> alignment in the middle of the structure happens. The problem when
> using the "packed" attribute is that most of the 16bits elements will
> be considered as 2 8bits elements and 32 bits elements will be
> considered as 4 8bits elements which is absolutely not what I want as
> these structures are mapped on internal registers that must be written
> in an atomic instruction.
>
> So the question is, what did I miss ? Is it the intended behavior for
> GCC >= 4.2 or does a patch already exist for fixing that.
Struct layout is specified by the processor ABI, so that different
compilers for the same processor can interoperate. When I compile
this code:
struct _s1 {
unsigned char e1;
unsigned char e2;
};
struct _s2 {
void *e1;
struct _s1 e2[2];
void *e3;
};
struct _s2 v = { 0, { { 1, 2 }, { 3, 4 } } , 0 };
for the x86, then I do not see the alignment you mention. So you need
to tell us what target you are using.
Ian
