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Re: Aw: Re: asking for __attribute__((aligned()) clarification


On Tue, 20 Aug 2019, "Markus Fröschle" wrote:

> Thank you (and others) for your answers. Now I'm just as smart as before, however.
> 
> Is it a supported, documented, 'long term' feature we can rely on or not?
> 
> If yes, I would expect it to be properly documented. If not, never mind.

I think it's properly documented in gcc-9:

  https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/Common-Type-Attributes.html

(the "old" behavior where the compiler would neither honor reduced alignment
nor issue a warning seems questionable, the new documentation promises a more
sensible approach)

In portable code one can also use memcpy to move unaligned data, the compiler
should translate it like an unaligned load/store when size is a suitable
constant:

  int val;
  memcpy(&val, ptr, sizeof val);

(or __builtin_memcpy when -ffreestanding is in effect)

Alexander

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