Re: [manual]: rawmemchr(3) and UB

[Alejandro Colomar <alx.manpages@gmail.com>]

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On 12/29/22 20:19, Alejandro Colomar via Libc-alpha wrote:
> Hi,
> 
> I was reading rawmemchr(3), and found some funny text:
> 
> RETURN VALUE
>         The  memchr()  and memrchr() functions return a pointer to the matching
>         byte or NULL if the character does not occur in the given memory area.
> 
>         The rawmemchr() function returns a pointer to the matching byte, if one
>         is found.  If no matching byte is found, the result is unspecified.
> 
> 
> Of course, if the byte is not found, the result is not unspecified, but rather 
> undefined, and a crash is very likely so maybe there's not even a result.  I 
> thought this might be a thinko of the manual page, but the glibc manual seems to 
> have similar text:
> 
> 
> <https://www.gnu.org/software/libc/manual/html_mono/libc.html#index-rawmemchr>
> "
> The rawmemchr function exists for just this situation which is surprisingly 
> frequent. The interface is similar to memchr except that the size parameter is 
> missing. The function will look beyond the end of the block pointed to by block 
> in case the programmer made an error in assuming that the byte c is present in 
> the block. In this case the result is unspecified. Otherwise the return value is 
> a pointer to the located byte.
> "
> 
> 
> That test can't be true, and the result of that function when there's no match 

s/test/text/

> can't be anything other than UB, and likely a crash.  Please fix the doc.
> 
> Cheers,
> 
> Alex

-- 
<http://www.alejandro-colomar.es/>

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