From: Phillip Wood <phillip.wood123@gmail.com>
To: Junio C Hamano <gitster@pobox.com>,
Phillip Wood via GitGitGadget <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org,
Johannes Schindelin <Johannes.Schindelin@gmx.de>,
Caspar Duregger <herr.kaste@gmail.com>,
Phillip Wood <phillip.wood@dunelm.org.uk>
Subject: Re: [PATCH 1/4] rebase -i: stop overwriting ORIG_HEAD buffer
Date: Sat, 31 Oct 2020 10:55:52 +0000 [thread overview]
Message-ID: <fa2d75ee-e692-a400-e9f7-8f13a5c220e8@gmail.com> (raw)
In-Reply-To: <xmqq7drbbcj5.fsf@gitster.c.googlers.com>
On 27/10/2020 21:10, Junio C Hamano wrote:
> "Phillip Wood via GitGitGadget" <gitgitgadget@gmail.com> writes:
>
>> From: Phillip Wood <phillip.wood@dunelm.org.uk>
>
> My initial impression after seeing the recent report about ORIG_HEAD
> was "hmph, these days, rebasing is done on detached HEAD and the
> final step updates the target branch only once, so @{1} is much
> easier to use---perhaps it is time to deprecate use of ORIG_HEAD?".
> After all, ORIG_HEAD was invented way before we had reflog, and
> given that one of the goal of reflog was to give more general
> recovery mechanism than going back one-step like ORIG_HEAD allowed
> us to, and "rebase" were taught to work on detached HEAD to make
> @{1} more useful, it would not be too bad to eventually retire
> ORIG_HEAD in a distant future, I thought.
Thanks for filling in the history. As reset sets ORIG_HEAD as well as
rebase it can be confusing so retiring it in the future maybe a good idea.
> But it is a good initiative anyway to make ORIG_HEAD again work as
> documented. Thanks for working on it.
>
>> After rebasing ORIG_HEAD is supposed to point to the old HEAD of the
>
> A comma after "rebasing".
Sure
>> rebased branch. Unfortunately the buffer storing the oid was
>> overwritten with a new oid before ORIG_HEAD was created. The buffer is
>> also used when writing .git/rebase-merge/orig-head which is used by
>> `rebase --abort` to restore the previous head. Luckily that file is
>> written before the buffer is overwritten. As we want the full oid
>> find_unique_abbrev() is replaced with oid_to_hex_r() rather than
>> find_unique_abbrev_r().
>
> The above is hard to read and understand. It is unclear where the
> observation of the current behaviour (which is often the explanation
> of the cause of the bug) ends and the description of new behaviour
> begins.
>
> ... old HEAD of the rebased branch. The code used
> find_unique_abbrev() to obtain the object name of the old HEAD
> and wrote to both .git/rebase-merge/orig-head (used by `rebase
> --abort` to go back to the previous state) and to ORIG_HEAD.
> The buffer find_unique_abbrev() gives back is volatile,
> unfortunately, and was overwritten after the former file is
> written but before ORIG_FILE is written, leaving an incorrect
> object name in it.
>
> Up to that point is the observation of the current code, which
> explains where the bug comes from. Please have a paragraph break
> after that, before explaining the solution, e.g.
>
> Avoid relying on the volatile buffer of find_unique_abbrev(),
> and instead supply our own buffer to keep the object name.
> Because we want to use the full object name, use oid_to_hex_r()
> instead of find_unique_abbrev_r() to do so.
That's much clearer thanks. I wonder if swapping to oid_to_hex_r()
rather than find_unique_abbev_r() is complicating this commit
unnecessarily as the code that is changed here is deleted in patch 4,
maybe we should do the switch there.
>> I think that all of the users of head_hash should actually be using
>> opts->orig_head instead as passing a string rather than a struct
>> object_id around is a hang over from the scripted implementation. This
>> patch just fixes the immediate bug and adds a regression test based on
>> Caspar's reproduction example. The users will be converted to use
>> struct object_id and head_hash removed in the next few commits.
>
> Makes sense.
>
>>
>> Reported-by: Caspar Duregger <herr.kaste@gmail.com>
>> Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
>> ---
>
> If you cite "Caspar's repro example" like that in the log message,
> it is incomplete to leave out a URL to the mail archive.
Good point I'll add a url
Thanks for your comments
Phillip
>> builtin/rebase.c | 10 +++++-----
>> t/t3404-rebase-interactive.sh | 11 +++++++++++
>> 2 files changed, 16 insertions(+), 5 deletions(-)
>>
>> diff --git a/builtin/rebase.c b/builtin/rebase.c
>> index eeca53382f..6def28a533 100644
>> --- a/builtin/rebase.c
>> +++ b/builtin/rebase.c
>> @@ -270,15 +270,15 @@ static int edit_todo_file(unsigned flags)
>> }
>>
>> static int get_revision_ranges(struct commit *upstream, struct commit *onto,
>> - struct object_id *orig_head, const char **head_hash,
>> + struct object_id *orig_head, char *head_hash,
>> char **revisions, char **shortrevisions)
>> {
>> struct commit *base_rev = upstream ? upstream : onto;
>> const char *shorthead;
>>
>> - *head_hash = find_unique_abbrev(orig_head, GIT_MAX_HEXSZ);
>> + oid_to_hex_r(head_hash, orig_head);
>> *revisions = xstrfmt("%s...%s", oid_to_hex(&base_rev->object.oid),
>> - *head_hash);
>> + head_hash);
>>
>> shorthead = find_unique_abbrev(orig_head, DEFAULT_ABBREV);
>>
>> @@ -327,7 +327,7 @@ static void split_exec_commands(const char *cmd, struct string_list *commands)
>> static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
>> {
>> int ret;
>> - const char *head_hash = NULL;
>> + char head_hash[GIT_MAX_HEXSZ];
>> char *revisions = NULL, *shortrevisions = NULL;
>> struct strvec make_script_args = STRVEC_INIT;
>> struct todo_list todo_list = TODO_LIST_INIT;
>> @@ -335,7 +335,7 @@ static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
>> struct string_list commands = STRING_LIST_INIT_DUP;
>>
>> if (get_revision_ranges(opts->upstream, opts->onto, &opts->orig_head,
>> - &head_hash, &revisions, &shortrevisions))
>> + head_hash, &revisions, &shortrevisions))
>> return -1;
>>
>> if (init_basic_state(&replay,
>> diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
>> index 07a1617351..1e56696e4f 100755
>> --- a/t/t3404-rebase-interactive.sh
>> +++ b/t/t3404-rebase-interactive.sh
>> @@ -1797,6 +1797,17 @@ test_expect_success 'todo has correct onto hash' '
>> test_i18ngrep "^# Rebase ..* onto $onto" actual
>> '
>>
>> +test_expect_success 'ORIG_HEAD is updated correctly' '
>> + test_when_finished "git checkout master && git branch -D test-orig-head" &&
>> + git checkout -b test-orig-head A &&
>> + git commit --allow-empty -m A1 &&
>> + git commit --allow-empty -m A2 &&
>> + git commit --allow-empty -m A3 &&
>> + git commit --allow-empty -m A4 &&
>> + git rebase master &&
>> + test_cmp_rev ORIG_HEAD test-orig-head@{1}
>> +'
>> +
>> # This must be the last test in this file
>> test_expect_success '$EDITOR and friends are unchanged' '
>> test_editor_unchanged
next prev parent reply other threads:[~2020-10-31 10:56 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-27 14:02 [PATCH 0/4] rebase -i: fix ORIG_HEAD handling Phillip Wood via GitGitGadget
2020-10-27 14:02 ` [PATCH 1/4] rebase -i: stop overwriting ORIG_HEAD buffer Phillip Wood via GitGitGadget
2020-10-27 21:10 ` Junio C Hamano
2020-10-31 10:55 ` Phillip Wood [this message]
2020-11-02 19:40 ` herr.kaste
2020-11-03 0:21 ` Junio C Hamano
2020-11-03 11:02 ` herr.kaste
2020-10-27 14:02 ` [PATCH 2/4] rebase -i: use struct object_id rather than looking up commit Phillip Wood via GitGitGadget
2020-10-27 14:02 ` [PATCH 3/4] rebase -i: use struct object_id when writing state Phillip Wood via GitGitGadget
2020-10-27 14:02 ` [PATCH 4/4] rebase -i: simplify get_revision_ranges() Phillip Wood via GitGitGadget
2020-11-04 15:29 ` [PATCH v2 0/4] rebase -i: fix ORIG_HEAD handling Phillip Wood via GitGitGadget
2020-11-04 15:29 ` [PATCH v2 1/4] rebase -i: stop overwriting ORIG_HEAD buffer Phillip Wood via GitGitGadget
2020-11-04 15:29 ` [PATCH v2 2/4] rebase -i: use struct object_id rather than looking up commit Phillip Wood via GitGitGadget
2020-11-04 15:29 ` [PATCH v2 3/4] rebase -i: use struct object_id when writing state Phillip Wood via GitGitGadget
2020-11-04 15:29 ` [PATCH v2 4/4] rebase -i: simplify get_revision_ranges() Phillip Wood via GitGitGadget
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