From: pinskia@gmail.com
To: Simon Marchi <simon.marchi@polymtl.ca>
Cc: "Paul_Koning@dell.com" <Paul_Koning@dell.com>,
"howarth.mailing.lists@gmail.com"
<howarth.mailing.lists@gmail.com>,
"gdb@sourceware.org" <gdb@sourceware.org>
Subject: Re: format string is not a string literal
Date: Thu, 26 Feb 2015 00:46:00 -0000 [thread overview]
Message-ID: <7A311B56-C424-4C4F-A0E4-B12B65131745@gmail.com> (raw)
In-Reply-To: <CAFXXi0=56gNf2GoSKkrx=bRArhjk+AhSbiu0crpdR3=df7B2BQ@mail.gmail.com>
On Feb 25, 2015, at 4:05 PM, Simon Marchi <simon.marchi@polymtl.ca> wrote:
>> I didn’t say it’s a bug, Andrew did. But I agree with him.
>>
>> My comment (“the code is legit”) simply meant that GDB uses variable formats for obvious valid reasons (so the format can vary, being user-supplied). Given that it’s intentional, the warning is not wanted.
>>
>> But that point is really applicable to printf, not vprintf. Andrew’s point is that checking formats for vprintf is not possible because you can’t know the argument list; only in printf do you see the arguments so you can match the types. So the bug is that format checking and complaining for non-literal formats should not be enabled at all for vprintf. That may be a header issue rather than a compiler issue, but either way, it’s not the right thing to do.
>>
>> paul
>
> I think the warning is relevant. If you instruct the compiler that
> inferior_debug takes a format string and format arguments (using a
> format attribute, as mentioned by Richard in the bug report), then it
> can check if the callers are doing something wrong.
>
> In the case of inferior_debug, the attribute should be
> __attribute__((format (printf, 2, 3)))
>
> By adding the attribute, you get nice warnings of this kind:
>
> test.c: In function ‘main’:
> test.c:17:2: warning: too many arguments for format [-Wformat-extra-args]
> inferior_debug (1, "pouet %d", 2, "hello");
>
> If the function is vprintf-style, it's similar but the last argument
> should be 0. It will push the argument check a level higher, where
> eventually they are explicitely defined printf-style. The doc is
> somewhere here [2] in the middle.
Then clang's warning should suggest putting the format attribute on that function rather than giving out a warning that seems like it is a bogus one.
Gcc does that iirc why not clang.
Thanks,
Andrew
>
> The warning also has some value because it will tell you if the string
> originally comes from a non-literal, which should be avoided [1].
>
> [1] http://en.wikipedia.org/wiki/Uncontrolled_format_string
> [2] https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html
>
> Simon
next prev parent reply other threads:[~2015-02-26 0:12 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-24 17:16 Jack Howarth
2015-02-24 18:04 ` Andrew Pinski
2015-02-24 18:18 ` Andrew Pinski
2015-02-25 9:42 ` Andrew Pinski
2015-02-25 7:58 ` Paul_Koning
2015-02-26 0:06 ` Jack Howarth
2015-02-26 0:12 ` Paul_Koning
2015-02-26 0:41 ` Simon Marchi
2015-02-26 0:46 ` pinskia [this message]
2015-02-26 2:31 ` Jack Howarth
2015-02-26 2:35 ` pinskia
2015-02-26 2:38 ` Simon Marchi
2015-02-26 8:39 ` Andrew Pinski
2015-02-26 8:46 ` Andrew Pinski
2015-02-26 9:52 ` Jack Howarth
2015-02-26 10:18 ` Andrew Pinski
2015-02-26 16:26 ` Pedro Alves
2015-02-26 17:44 ` Jack Howarth
2015-02-26 19:55 ` Pedro Alves
2015-02-27 2:22 ` Paul Smith
2015-02-26 18:34 ` Paul Smith
2015-02-26 19:41 ` Pedro Alves
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=7A311B56-C424-4C4F-A0E4-B12B65131745@gmail.com \
--to=pinskia@gmail.com \
--cc=Paul_Koning@dell.com \
--cc=gdb@sourceware.org \
--cc=howarth.mailing.lists@gmail.com \
--cc=simon.marchi@polymtl.ca \
/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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).