Jeff King <p...@peff.net> writes:
> I agree it's not right, though. I think the original is questionable,
> too. It takes a pointer into the middle of partial_commit->buffer and
> attaches it to a strbuf. That's wrong because:
> 1. It's pointing into the middle of an allocated buffer, not the
> 2. We do not own partial_commit->buffer in the first place.
> So any call to strbuf_detach on the result would be disastrous.
You are right. Where did this original crap come from X-<...
> ... and it
> doesn't cause a bug in practice because the only use of the strbuf is to
> pass it as a const to create_notes_commit.
> I feel like the most elegant solution is for create_notes_commit to take
> a buf/len pair rather than a strbuf, but it unfortunately is just
> feeding that to commit_tree. Adjusting that code path would affect quite
> a few other spots.
> The other obvious option is actually populating the strbuf, but it feels
> ugly to have to make a copy just to satisfy the function interface.
> Maybe a cast and a warning comment are the least evil thing, as below? I
> dunno, it feels pretty wrong.
Yeah, it does feel wrong wrong wrong. Perhaps this big comment
would serve as a marker for a low-hanging fruit for somebody else to
fix it, e.g. by using strbuf-add to make a copy, which would be the
easiest and safest workaround?
> diff --git a/notes-merge.c b/notes-merge.c
> index 94a1a8a..1f3b309 100644
> --- a/notes-merge.c
> +++ b/notes-merge.c
> @@ -671,7 +671,7 @@ int notes_merge_commit(struct notes_merge_options *o,
> DIR *dir;
> struct dirent *e;
> struct strbuf path = STRBUF_INIT;
> - char *msg = strstr(partial_commit->buffer, "\n\n");
> + const char *msg = strstr(partial_commit->buffer, "\n\n");
> struct strbuf sb_msg = STRBUF_INIT;
> int baselen;
> @@ -719,7 +719,15 @@ int notes_merge_commit(struct notes_merge_options *o,
> strbuf_setlen(&path, baselen);
> - strbuf_attach(&sb_msg, msg, strlen(msg), strlen(msg) + 1);
> + /*
> + * This is a bit tricky. We should not be attaching msg, which
> + * is not owned by us and is not even the start of a heap buffer, to a
> + * strbuf. But the create_notes_commit interface really wants
> + * a strbuf, even though it will only ever use it as a buf/len pair and
> + * never modify it. So this is tentatively safe as long as nobody ever
> + * modifies, detaches, or releases the strbuf.
> + */
> + strbuf_attach(&sb_msg, (char *)msg, strlen(msg), strlen(msg) + 1);
> create_notes_commit(partial_tree, partial_commit->parents, &sb_msg,
> if (o->verbosity >= 4)
> I'm still confused and disturbed that my gcc is not noticing this
> obvious const violation. Hmm, shutting off ccache seems to make it work.
> Doubly disturbing.
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