I can't add much to Michael's summary other than to say that
we are working on getting compatibility between the two toolsets,
particularly where interprettations of standards make them miss
(for example in Dwarf-II).
Dave
Michael Nonweiler wrote:
> At 18:45 15/09/00 +0200, Xavier DEBREUIL wrote:
> > Consider the following structure :
> > struct foo{
> > u8 buf[5];
> > u8 frame[0];
> > } ;
>
> (snipped)
> sizeof(foo) == 8 with arm-linux-gcc, or 5 with (x86?) gcc.
>
> You are seeing that the minimum structure alignment is 4 for the ARM
> compiler, but 1 for the x86 gcc.
>
> This is due to an historical optimisation choice, made for the original
> commercial ARM compiler. Somebody thought they could compile faster code
> for ARM by making this restriction. For example, you can use a word
> aligned memcpy for "foo" on ARM, but you have to use the generic version on
> x86.
>
> I believe arm-gcc maintainers chose to do the same for object-level
> compatibility.
>
> Unfortunately changing this breaks compatibility, So if you change it for
> your own code, you may not be able to use some parts of glibc anymore. It
> could fail in bad ways. (Unless you recompile everything on your system
> yourself.)
>
> ARM has changed this in our tool-chain, and we took a backwards
> compatibility hit when we did so.
>
> So "arm-gcc" is not compatible with the ARM ADS tool-chain, as a result.
>
> Phil - are there any plans to change this in a future gcc?
>
> Efforts are still underway to document this as a standard. Currently this
> is not part of either the ARM ATPCS or the ARM ELF specs, so it's not
> surprising there are compatibility problems.
>
> There's a similar problem with 4 byte alignment of global variables.
>
> > Is there any option for the arm-linux-gcc to give the same result as the
> gcc ?
>
> "-mstructure-size-boundary=8" (for 1 byte = 8 bits alignment)
>
> Be very careful with this, because it will break compatibility with some
> libraries, and other object files.
>
> Cheers,
>
> Michael Nonweiler.
>
> (speaking for myself)
>
> _______________________________________________
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