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From: Jonny Grant <jg@jguk.org>
To: Florian Weimer <fw@deneb.enyo.de>
Cc: linux-man <linux-man@vger.kernel.org>,
	Michael Kerrisk <mtk.manpages@gmail.com>
Subject: Re: strlen
Date: Sat, 5 Sep 2020 00:14:35 +0100	[thread overview]
Message-ID: <017a5a66-ba66-7cc8-c607-f851c2e54fc4@jguk.org> (raw)
In-Reply-To: <87lfhpgxf8.fsf@mid.deneb.enyo.de>



On 04/09/2020 20:21, Florian Weimer wrote:
> * Jonny Grant:
> 
>> Hello
>>
>> https://man7.org/linux/man-pages/man3/strlen.3.html
>>
>> Is it possible to clarify :-
>>
>> * glibc will SIGSEGV if 's' is NULL
>> * there are no ERROR returns
> 
> That would be misleading.  Whether strlen (NULL) is undefined also
> depends on the compiler.  They know that the argument cannot be zero
> and optimize accordingly.
> 

Hi,

Do you know a compiler that has a different behaviour? I only tested gcc and clang. How would a compiler optimise?

The header has non-null attribute for the compiler (ie gcc) to use to give a nice warning

str.c:6:8: warning: null argument where non-null required (argument 1) [-Wnonnull]
    6 | return strlen(NULL);

However, if the implementation gets NULL it still crashes.

I was using -fno-builtin-strlen so it was glibc, but the __builtin_strlen ha SEGV just like glibc

clang is the same as gcc.

So it feels like it's pretty clear, there is no NULL check, can this be documented? 

Jonny

  reply	other threads:[~2020-09-04 23:14 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-04 18:01 strlen Jonny Grant
2020-09-04 19:21 ` strlen Florian Weimer
2020-09-04 23:14   ` Jonny Grant [this message]
2020-09-05  7:12     ` strlen Florian Weimer
2021-07-06 20:30       ` strlen Jonny Grant
2021-07-06 22:11         ` strlen Florian Weimer
2021-07-07 11:36           ` strlen Jonny Grant
2021-07-07 12:22             ` strlen Alejandro Colomar (man-pages)
2021-07-07 12:31               ` strlen Alejandro Colomar (man-pages)
2021-07-07 13:31                 ` strlen Jonny Grant
2021-07-07 16:57                   ` strlen Alejandro Colomar (man-pages)
2021-07-07 17:23                     ` strlen Alejandro Colomar (man-pages)
2021-07-07 17:33                       ` strlen Alejandro Colomar (man-pages)
2021-07-09 13:48                         ` strlen Jonny Grant
2021-07-08 10:07                     ` strlen Jonny Grant
2021-07-08 11:06                       ` strlen Alejandro Colomar (man-pages)
2021-07-08 12:13                         ` strlen Xi Ruoyao
2021-07-08 23:49                         ` strlen Segher Boessenkool
2021-07-09 13:54                           ` strlen Jonny Grant
2021-07-09 14:17                             ` strlen Alejandro Colomar (man-pages)
2021-07-09 16:11                               ` strlen Xi Ruoyao
2021-07-10  1:00                               ` strlen Segher Boessenkool
2021-07-09 10:50                         ` strlen Jonny Grant
2021-07-09 11:27                           ` strlen Alejandro Colomar (man-pages)
2021-07-09 11:43                             ` strlen Alejandro Colomar (man-pages)
     [not found]                         ` <1627912755.3783669.1625745946723@mail.yahoo.com>
     [not found]                           ` <59a70222-a46f-1e65-c9db-6c9e577c8adc@126.com>
2021-07-09 17:26                             ` strlen Martin Sebor
2021-07-09 20:19                               ` strlen Alejandro Colomar (man-pages)
2021-07-09 20:44                     ` strlen Jonny Grant
2021-07-10 18:37                       ` strlen Alejandro Colomar (man-pages)
2021-07-10 20:49                         ` strlen Jonny Grant
2021-07-10 21:36                           ` strlen Alejandro Colomar (man-pages)
2021-07-12 21:16                             ` strlen Jonny Grant

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