Re: packObjectsHook and the git executable

From: Bryan Turner <bturner@atlassian.com>
Date: Jan 30, 2020, 07:38 UTC
Message-ID: <CAGyf7-HkUV43A79DKiDVvKnW5vuwsFz0KnZKj9bBQYc906VONg@mail.gmail.com>
In-Reply-To: <20200130071102.GA2189233@coredump.intra.peff.net>

On Wed, Jan 29, 2020 at 11:11 PM Jeff King <peff@peff.net> wrote:

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>
> On Wed, Jan 29, 2020 at 05:00:18PM -0800, Bryan Turner wrote:
>
> > In upload-pack.c, when Git invokes the packObjectsHook, it's
> > hard-coded to pass "git". Unless it modifies the PATH environment
> > variable, though, if the script were to invoke the provided command
> > line as-is, it may end up running a different version of Git than the
> > version being used to run upload-pack (or http-backend).
>
> We do modify PATH to put git's exec-path at the start. This happens in
> setup_path(), which is called by the main "git" executable (so "git
> upload-pack" before it hits cmd_upload_pack()).

Thanks, that's a missing piece I'd overlooked (and explains why everything is written the way it is, to use "git").

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>
> Programs which are invoked directly as "git-upload-pack" need to call
> that function on their own (which happens when upload-pack is invoked
> over ssh). But upload-pack and http-backend do that.
>
> > Is there any way the packObjectsHook could be passed the "right" git
> > executable? Or am I missing some surrounding context that means
> > executing "git" is somehow guaranteed to invoke the "right" binary?
> > (Perhaps this same PATH-related caveat applies to other places where
> > Git invokes itself recursively?)
>
> I think all is working as designed, but if you have a reproducible case
> where we run the "wrong" git, I can take a look at it.

I suspect it's a case of a broken Git build. Not that Git is doing
anything wrong, or has any problems with its build, to be clear--I
mean instead that someone ran a local build and didn't set it up
"right". Correct me if I'm wrong but:
- If the GIT_EXEC_PATH environment variable isn't set, Git will use
the path that was compiled in when it was built
- If that Git is installed in a different path (i.e. compiled for
/usr/local but installed in /opt), the compiled-in exec path may not
exist or not contain "git"
- In that case, "git" gets run from wherever it's found in $PATH and
you get whatever version that happens to be

Does something like that seem like it could happen?

Thanks as always for your insights! Bryan

>
> -Peff