This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: Using BIGGEST_ALIGNMENT to remove alignment constraints
- From: Eric Botcazou <ebotcazou at adacore dot com>
- To: Paulo Matos <pmatos at broadcom dot com>
- Cc: gcc at gcc dot gnu dot org
- Date: Tue, 26 Nov 2013 18:13:49 +0100
- Subject: Re: Using BIGGEST_ALIGNMENT to remove alignment constraints
- Authentication-results: sourceware.org; auth=none
- References: <19EB96622A777C4AB91610E763265F463BE7E8 at SJEXCHMB14 dot corp dot ad dot broadcom dot com>
> I am slightly confused about the BIGGEST_ALIGNMENT docs which state:
> "Biggest alignment that any data type can require on this machine, in bits.
> Note that this is not the biggest alignment that is supported, just the
> biggest alignment that, when violated, may cause a fault."
>
> What kind of fault would this be?
Unaligned memory access fault.
> I am tempted to set BIGGEST_ALIGNMENT to 8 so I can force GCC to just align
> the data at any byte boundary. Would this be a fair use of
> BIGGEST_ALIGNMENT?
Yes, you may set BIGGEST_ALIGNMENT to 8 if unaligned memory accesses can never
generate a fault on the architecture. But, in practice, you might want to
take into account performance considerations.
--
Eric Botcazou