ARM and padding

Ola Liljedahl olli@enea.se
Tue Jul 18 02:28:00 GMT 2000


You are transferring a binary structure from one architecture to another
using the compiler's struct layout as the format of the packet?!?

Don't expect this to work more than in some rare instance (depending on
the involved processor architectures and compilers).

You need some more protocol layer to get this communication reliable. Or
some packet format which is inherently more portable.
--
	Ola Liljedahl

jens.ohlund@secrc.abb.se wrote:
> 
> Hi !
> 
> It doesn't help. I've made a struct like this:
> struct
> {
>   unsigned char buf[250] __attribute__ ((packed));
>   unsigned char currPos __attribute__ ((packed));
>   unsigned int  remainingBytes __attribute__ ((packed));
>   unsigned char state __attribute__ ((packed));
> } __attribute__ ((packed)) lowRx;
> 
> And still, it's on the adresses:
> &buf[] = 0x241E0
> &currPos = 0x242DA
> &remainingBytes = 0x242DC
> &state = 0x242DF
> 
> Which makes the sizes:
> buf -> currPos =  250
> currPos -> remainingBytes = 2 !!!!!
> remainingBytes -> state = 4
> 
> currPos -> remainingBytes should only be 1.
> 
> This is just one struct out of many, with the same problem. I can change Some of them, as this example. But not many compared to
> amount of troublesome structs.
> 
> yours
> Jens
> 
> crossgcc-owner@sources.redhat.com
> 2000-07-18 10:38
> 
> To:   jens.ohlund@secrc.abb.se
> cc:   crossgcc@sourceware.cygnus.com
> Subject:  Re: ARM and padding
> 
> Security Level:?         Internal
> 
> >How do I tell the compiler that the structs are to be packed ?
> 
> __attribute__ (( packed )).  See the gcc manual.
> 
> p.
> 
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