From: Danh Doan <congdanhqx@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: Elia Pinto <gitter.spiros@gmail.com>, git@vger.kernel.org
Subject: Re: [PATCH 31/32] commit-graph.c: fix code that could convert the result of an integer multiplication to a larger type
Date: Thu, 7 Nov 2019 11:06:05 +0700 [thread overview]
Message-ID: <20191107040605.GA8096@danh.dev> (raw)
In-Reply-To: <xmqqtv7gs6g3.fsf@gitster-ct.c.googlers.com>
On 2019-11-07 12:37:00 +0900, Junio C Hamano wrote:
> Danh Doan <congdanhqx@gmail.com> writes:
>
> > On 2019-11-06 11:23:00 +0900, Junio C Hamano wrote:
> >> > @@ -1454,7 +1454,7 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
> >> > num_chunks);
> >> > ctx->progress = start_delayed_progress(
> >> > progress_title.buf,
> >> > - num_chunks * ctx->commits.nr);
> >> > + (uint64_t)num_chunks * ctx->commits.nr);
> >>
> >> Hmph, do we need this? I understand that the second parameter to
> >> the callee is u64, so the caller needs to come up with u64 without
> >> overflow, but doesn't that automatically get promoted?
> >
> > Neither num_chunks nor ctx->commits.nr is promoted because both of
> > them are int. The result of `num_chunks * ctx->commits.nr' will be int
> > and will be promoted to u64 to pass to caller.
>
> Ah, yes. Thanks.
>
> The commit title is about "integer multiplication", but can the same
> issue arise with addition and subtraction as well, by the way?
Yes, the same issue will arise with all binary (and ternary) arithmetic operators
(+, -, *, /, %, ^, &, |, <<, >> and ?:).
IIRC, gcc doesn't have any warning for this kind of issue.
Microsoft Visual Studio (2017+) has C26451 for this.
https://docs.microsoft.com/en-us/visualstudio/code-quality/c26451?view=vs-2017
If our friends at Microsoft could help, we can check the remaining one
in our codebase.
--
Danh
next prev parent reply other threads:[~2019-11-07 4:06 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-04 9:59 [PATCH 30/32] ident.c: fix LGTM warning on the possible abuse of the '=' operator Elia Pinto
2019-11-04 9:59 ` [PATCH 31/32] commit-graph.c: fix code that could convert the result of an integer multiplication to a larger type Elia Pinto
2019-11-06 2:23 ` Junio C Hamano
2019-11-07 2:23 ` Danh Doan
2019-11-07 3:37 ` Junio C Hamano
2019-11-07 4:06 ` Danh Doan [this message]
2019-11-07 12:49 ` Johannes Schindelin
2019-11-07 12:45 ` Johannes Schindelin
2019-11-04 9:59 ` [PATCH 32/32] date.c: fix code that may overflow 'int' before it is converted to 'time_t' Elia Pinto
2019-11-04 10:26 ` [PATCH 30/32] ident.c: fix LGTM warning on the possible abuse of the '=' operator SZEDER Gábor
2019-11-04 13:55 ` Elia Pinto
2019-11-04 15:11 ` Phillip Wood
2019-11-04 19:55 ` Elia Pinto
2019-11-06 2:16 ` Junio C Hamano
2019-11-06 11:32 ` Johannes Schindelin
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191107040605.GA8096@danh.dev \
--to=congdanhqx@gmail.com \
--cc=git@vger.kernel.org \
--cc=gitster@pobox.com \
--cc=gitter.spiros@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.