Re: git 2.16.0 segfaults on clone of specific repo

[Eric Sunshine <sunshine@sunshineco.com>]

On Thu, Jan 18, 2018 at 9:47 PM, brian m. carlson
<sandals@crustytoothpaste.net> wrote:
> On Thu, Jan 18, 2018 at 07:15:56PM -0500, Eric Sunshine wrote:
>> On Thu, Jan 18, 2018 at 3:55 PM, Александр Булаев
>> <aleks.bulaev@gmail.com> wrote:
>> > I found that git 2.16.0 segfaults on clone of vim-colorschemes repo.
>>
>> I can confirm that this crashes on MacOS; it does not crash on Linux or BSD.
>>
>> git-bisect places blame on eb0ccfd7f5 (Switch empty tree and blob
>> lookups to use hash abstraction, 2017-11-12).
>
> I unfortunately don't have a macOS system to test with, and I've
> compiled with both gcc and clang on my Debian system and, as you
> mentioned, it doesn't fail there.
>
> I have a guess about what the problem might be.  Can you try this patch
> and see if it fixes things?

That does fix the crash. Thanks for the quick diagnosis.

Can the commit message go into more detail as to why this was crashing
(or your speculation about why)? Perhaps give more detail about what
'clone' is doing that led to the crash.

> -- >8 --
> From 10b690241619a452634b31fbc5ccd054a4f6e5ec Mon Sep 17 00:00:00 2001
> From: "brian m. carlson" <sandals@crustytoothpaste.net>
> Date: Sun, 14 Jan 2018 18:26:29 +0000
> Subject: [PATCH] repository: pre-initialize hash algo pointer
>
> There are various git subcommands (among them, clone) which don't set up
> the repository but end up needing to have information about the hash
> algorithm in use.  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>
> ---
>  repository.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/repository.c b/repository.c
> index 998413b8bb..f66fcb1342 100644
> --- a/repository.c
> +++ b/repository.c
> @@ -5,7 +5,7 @@
>
>  /* The main repository */
>  static struct repository the_repo = {
> -       NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, &the_index, NULL, 0, 0
> +       NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, &the_index, &hash_algos[GIT_HASH_SHA1], 0, 0
>  };
>  struct repository *the_repository = &the_repo;
>
> --