Re: [PATCH] repository: pre-initialize hash algo pointer

[Eric Sunshine <sunshine@sunshineco.com>]

On Thu, Jan 18, 2018 at 11:18 PM, brian m. carlson
<sandals@crustytoothpaste.net> wrote:
> There are various git subcommands (among them, clone) which don't set up
> the repository (that is, they lack RUN_SETUP or RUN_SETUP_GENTLY) but
> end up needing to have information about the hash algorithm in use.
> Because the hash algorithm is part of struct repository and it's only
> initialized in repository setup, we can end up dereferencing a NULL
> pointer in some cases if we call one of these subcommands and look up
> the empty blob or empty tree values.
>
> In the future, we can add a command line option for this or read it from
> the configuration, but until we're ready to expose that functionality to
> the user, simply initialize the repository structure to use the current
> hash algorithm, SHA-1.
>
> Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
> ---
> I'm still quite mystified as to why this is working on Linux and not
> macOS, but I can only guess that compilers are just very advanced and
> have somehow concluded that we would clearly never dereference a NULL
> pointer, so they picked the only non-NULL value.

Now that we know (due to Duy's excellent detective work[1]) that the
trigger is files with names differing only in case on case-insensitive
filesystems, the commit message can be updated appropriately.

> I haven't included a test because I have no way to reproduce the issue.
> This patch is the first from a series I'm working on where I do expand
> the use of the hash struct and therefore caused a segfault on clone, so
> I can imagine what's going on without having a way to prove it affects
> this particular case.
>
> If someone with access to macOS can provide a test, I'd be very
> grateful.

Done. Find the test here[2]. It fails without your fix on MacOS and
(presumably) Windows, and succeeds with the fix.

> My apologies for the error and inconvenience.

[1]: https://public-inbox.org/git/CACsJy8BTFm_0sv=roL1OKKW=1DyU3vqD50NKyHg3KQ7G+mAepQ@mail.gmail.com/
[2]: https://public-inbox.org/git/20180119074001.GA55929@flurp.local/