Re: [PATCH 1/2] compat: move unaligned helpers to bswap.h

On Thu, Jan 23, 2014 at 11:41:18AM -0800, Jonathan Nieder wrote:

Jeff King wrote:

quoted

Commit d60c49c (read-cache.c: allow unaligned mapping of the
index file, 2012-04-03) introduced helpers to access
unaligned data. Let's factor them out to make them more
widely available.

While we're at it, we'll give the helpers more readable
names, add a helper for the "ntohll" form, and add the
appropriate Makefile knob.

Weird.  Why wasn't git broken on the relevant platforms before (given
that no one has been setting NEEDS_ALIGNED_ACCESS for them)?

Because most of our data structures support aligned access. Thomas
mentioned this as a potential issue earlier, and I said in a re-roll
cover letter:

  I did not include the NEEDS_ALIGNED_ACCESS patch. I note that we do
  not even have a Makefile knob for this, and the code in read-cache.c
  has probably never actually been used. Are there real systems that
  have a problem? The read-cache code was in support of the index v4
  experiment, which did away with the 8-byte padding. So it could be
  that we simply don't see it, because everything is currently aligned.

I think it was a bug waiting to surface if index v4 ever got wide use.

-Peff