linux-kernel - Re: gcc fixed size char array initialization bug

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Date:	Thu, 02 Aug 2007 15:42:29 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: gcc fixed size char array initialization bug - known?

Guennadi Liakhovetski wrote:
> On Thu, 2 Aug 2007, Andi Kleen wrote:
> 
>> Guennadi Liakhovetski <g.liakhovetski@....de> writes:
>>
>>> 	char c[4] = "0123";
>>> and - a wonder - no warning. 
>> It's required by the C standard.
>>
>> 6.7.8.14 of C99:
>> ``
>> An array of character type may be initialized by a character string literal, optionally
>> enclosed in braces. Successive characters of the character string literal (including the
>> terminating null character if there is room or if the array is of unknown size) initialize the
>> elements of the array.
>> ''
>>
>> Note the "if there is room".
>>
>> I believe the rationale is that it still allows to conveniently initialize 
>> non zero terminated strings.
> 
> Right, I accept that it will compile, but I don't understand why "01234" 
> produces a warning and "0123" doesn't? Don't think C99 says anything about 

Because 5 characters will not fit in a 4 character array, even without 
the null terminator.

> that. And, AFAIU, using structs with fixed-size char array we more or less 
> rely on the compiler warning us if anyone initializes it with too long a 
> string.
> 
> Also interesting, that with
> 
> 	char c[4] = "012345";
> 
> the compiler warns, but actually allocates a 6-byte long array...
> 
> Thanks
> Guennadi


-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/