Show number of padding bytes in data structures

[Frank Winklmeier]

Paul Koning wrote:
>>>>>> "Frank" == Frank Winklmeier <frank.winklmeier@cern.ch> writes:
> 
>  Frank> Hi, is there any way of using one of the binutils to show the
>  Frank> additional padding bytes that a compiler inserted into a
>  Frank> struct/class to make it align according to the systems memory
>  Frank> alignment rules? Or is this information lost once the compiler
>  Frank> has done its job?
> 
>  Frank> For example, for the following data structure compiled on x64,
>  Frank> I would expect the tool to tell me that the compiler added 4
>  Frank> padding bytes:
> 
>  Frank> class MyData { int i; double d; };
> 
> I don't know about any binutils.  You can easily do this in gdb if
> your binary still contains the necessary debug data.
> 
> For example:
> 
>     print ((int)(((MyData *)0)->d))-((int)((((MyData *)0)->i)+1))
> 
> will do the job for the example you gave.
> 
>      paul
> 

Hi Paul,

thanks for your reply. I was hoping for a more efficient way for a large 
  number of classes and structs. Ideally, I would like to compare the 
number of padding bytes for a library compiled in 32 and 64 bit and see 
how many bytes got wasted for each data structure due to the different 
memory alignment.

Frank