Re: format string is not a string literal

pinskia
2015-02-26T00:46:44Z

> On Feb 25, 2015, at 4:41 PM, Jack Howarth <howarth.mailing.lists@gmail.com> wrote:
>
> Andrew,
> See the additional comments from the llvm.org clang developers at...
>
> http://llvm.org/bugs/show_bug.cgi?id=22701#c5

Then put this warning under a different flag. Anyways clang is broken and gdb should not change due to a broken compiler.

Thanks,
Andrew

>
> Jack
>
>> On Wed, Feb 25, 2015 at 7:12 PM, <pinskia@gmail.com> wrote:
>>
>>
>>
>>
>> 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