Xen devel - Mar 2005 - PACKED in structure is xen.h - newbie (OT)

Hello ,

I am trying to learn a liitle about Xen by reading the source code.

I see that ''PACKED'' appears in many structures;

for example :  in xen/include/public/xen.h:

typedef struct
{
    memory_t ptr;    /* Machine address of PTE. */
    memory_t val;    /* New contents of PTE.    */
} PACKED mmu_update_t;


What is this ''PACKED''? is it  the __attribute__ ((__packed__))
of gcc (or
something near)?

Is there somewhere  a macro in Xen which defines it?  (or is it a part of 
some gcc extension?)

Regards,
Sting

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On 30 Mar 2005, at 12:20, sting sting wrote:
> What is this ''PACKED''? is it  the __attribute__
((__packed__)) of gcc
> (or something near)?
>
> Is there somewhere  a macro in Xen which defines it?  (or is it a part 
> of some gcc extension?)
It means that the compiler will not add extra padding in between 
adjacent fields in teh struct. I''ve been convinced this is not the best
way to define the interface structures, so all the PACKED declarations 
will be disappearing in the near future!

  -- Keir


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