Re: t9210-scalar.sh fails with SANITIZE=undefined

From: Jeff King <peff@peff.net>
Date: Sep 22, 2022, 19:12 UTC
Message-ID: <Yyyzk3FVjmms7dkO@coredump.intra.peff.net>
In-Reply-To: <ff921c34-139a-9e2b-ca1f-d6f9f7213d1b@github.com>

On Thu, Sep 22, 2022 at 08:35:22AM -0400, Derrick Stolee wrote:

Show 21 quoted lines

> > I didn't dig further. It's obviously new in v2.38.0-rc1, but I'm not
> > sure it's a show-stopper. It _might_ have been there all along, and is
> > just now surfacing. Or it might be in an existing experimental feature
> > that just wasn't exercised enough in the tests. Or if it really is new
> > in scalar, then it will only hurt people using scalar, which didn't
> > exist before. So I don't think it's a regression in the strictest sense,
> > but it might be nice to get a more accurate understanding of the problem
> > before the release.
> 
> Interesting find!
> 
> Here are the index-related settings that Scalar sets as of -rc1:
> 
> * core.preloadIndex=true
> * index.threads=true
> * index.version=4
> 
> My gut feeling is that index.version=4 might be the culprit. I thought
> we tested GIT_TEST_INDEX_VERSION=4 in some CI modes, but apparently we
> do not. Do you get the same error in other tests with that environment
> variable?

Yeah, that seems by far the most likely of those three. And indeed, running with GIT_TEST_INDEX_VERSION=4 causes even t0000 to fail with the same problem. A minimal reproduction in git.git is just:

  make SANITIZE=undefined
  git clone . tmp
  cd tmp
  rm .git/index
  export GIT_INDEX_VERSION=4
  ../git reset --hard ;# ok, writes v4 index
  ../git reset --hard ;# fails reading unaligned v4 index

So it seems like a problem with the v4 format in general. Which...yikes.

-Peff