Re: char alignment on ARM

[Mike Stump <mrs at apple dot com>]

On Jan 17, 2007, at 5:23 AM, Inder wrote:
> void make(char* a) { *(unsigned long*)a = 0x12345678; }

> stating address of the char array now starts from an unaligned  
> address and is acessed by the instruction
>   strb    r3, [fp, #-26]
>
> which gives a very wrong result

> Is the compiler doing a right thing or is it a bug?

You asked for char alignment, and your program requires long  
alignment, your program is now, and always has been buggy.  The  
manual covers how to fix this, if you want to use __attribute__,  
otherwise, you can use a union to force any alignment you want.  So,  
in your case, yes, the compiler is doing the right thing.

If you were on a processor that handled misaligned data slowly, and  
you saw a general performance drop because of this, I'd encourage you  
to file a bug report as it might be a bug, if the results you see  
apply generally.

You're asking about behavioral differences in compilers that are  
really old.  You increase the odds that you can have these types of  
questions answered here, if you track and test mainline and ask the  
week the behavior changes, if it isn't obvious from glancing at the  
list for the past week.  :-)