linux-kernel - Re: [PATCH] ubi: kill homegrown endian macros

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Message-Id: <315d22bffba5fe251dbe60e4e0d5ced0@kernel.crashing.org>
Date:	Sat, 19 May 2007 14:24:36 +0200
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Matthieu CASTET <castet.matthieu@...e.fr>,
	"John Anthony Kazos Jr." <jakj@...-k-j.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ubi: kill homegrown endian macros

>> It's not the compiler who decides -- struct layout is
>> dictated by the ABI you're compiling for.
>
> This is true in the case of externally-visible stuff. I think the
> compiler is permitted to violate the ABI for purely unit-internal 
> things
> if it makes sense though, isn't it?

Sure.  It isn't "violating the ABI" in that case though,
to be perfectly clear.

> Besides, in the case of the Linux kernel the ABI in question could be
> one of many. It could even be a new one which was added a couple of
> weeks ago, and which I had no _chance_ of considering.

Of course.

> The rule stands -- empirical testing of what the compiler will do isn't
> usually the right answer.

It is *never* the right answer.  You should always write
your code so that it will do the right thing no matter
what the compiler decides to do to it.


Segher

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