[U-Boot] packed attribute problem

[Wolfgang Denk]

Dear Vipin Kumar,

In message <4CA9ACAA.2020001 at st.com> you wrote:
>
> >> This writel results in writing byte by byte on the address pointed to by status_reg.
> >> This problem is visible with both gcc version 4.4.1 as well as 4.5.0
> > 
> > I bet this is on some ARM system?
> 
> Yes, it is on an ARM system (CortexA9). But I still feel that since I am creating 
> a new u32 * status_reg, the code should not use any intelligence and use the pointer 
> only to produce an str instruction in the form
> 	str r0, [r1]
> 
> But it retains the packed property of the structure even with a new u32 ponter 
> typecasted to u32 *
> 	u32 * status_reg = (u32 *)xyz->x;
> 
> A writel to status_reg results in byte by byte writing

I agree with you. I always considered such behaviour of the ARM C
compiler a bug, and still do.  However, people with better knowledge
of the ARm architecture than me might be able to explain why the
responsible PTB consider this to be a good and necessary "feature" of
th compiler.

> > Hm... Why do these structs have any "__attribute__ ((packed))" at all?
> 
> Even I could not understand that very well

Eventually alignment of these structs cannot be guaranteed?



Best regards,

Wolfgang Denk

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