Re: [avr-gcc-list] -fpacked-struct compiler option

[E. Weddington]

Anton Erasmus wrote:

> Hi,
>
> The makefile example that comes with WinAVR uses the 
> -fpacked-struct compiler option.
>
> The gcc documentation has the following warning on this option:
> Warning: the -fpack-struct switch causes GCC to generate code that is not binary 
> compatible with code generated without that switch. Additionally, it makes the code 
> suboptimial. Use it to conform to a non-default application binary interface.
>
>  
1. We don't have to worry much about "binary compatibility" as AVR 
projects are compiled into one image, i.e. no loading of external, 3rd 
party binary images.
2. AFAIK it is only suboptimal on targets that have alignments > 1.

> So why is this option used in the example makefile. I would have thought that 
> with the
> avr being an 8-bit architecture that structures would automatically be packed, 
> as there
> is no advantage in accessing non-byte alligned data compared to accessing byte 
> alligned data.
>
>  
Um, perhaps just being paranoid? Seemed like a good thing to do at the 
time? It shouldn't hurt anything to have it in?
Anybody have any other reasoning they'd like to throw around? :-)

Eric