Date: Wed, 24 Jan 2018 07:17:27 +0300 From: Yuri Pankov <yuripv@icloud.com> To: Kyle Evans <kevans@freebsd.org> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: libc/regex: r302824 added invalid check breaking collating ranges Message-ID: <2c9ebf81-c06a-13ed-9cf9-9b42a00c76ee@icloud.com> In-Reply-To: <CACNAnaGioTGUFpNEakT-b88f_pa7ZaAXBPp09ruTzD8HFWWQfQ@mail.gmail.com> References: <a0d9abd8-19b8-cdf6-5451-e184fa182b38@icloud.com> <e192f9f7-9d9c-d1e3-8db4-02226ffa23d3@icloud.com> <CACNAnaF2aJ5EqLSCLTRkGH%2Bq5SYMmxD1dygGd8NFrkA9STJX8A@mail.gmail.com> <f17e0e80-dc27-568a-2896-5cb38ebc470f@icloud.com> <CACNAnaGioTGUFpNEakT-b88f_pa7ZaAXBPp09ruTzD8HFWWQfQ@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tue, Jan 23, 2018 at 01:22:04PM -0600, Kyle Evans wrote:
> On Tue, Jan 23, 2018 at 1:10 PM, Yuri Pankov <yuripv@icloud.com> wrote:
>> On Tue, Jan 23, 2018 at 08:10:32AM -0600, Kyle Evans wrote:
>>>
>>> On Mon, Jan 22, 2018 at 11:36 PM, Yuri Pankov <yuripv@icloud.com> wrote:
>>>>
>>>> On Tue, Jan 23, 2018 at 03:53:19AM +0300, Yuri Pankov wrote:
>>>>>
>>>>>
>>>>> (CCing Kyle as he's working on regex at the moment and not because he
>>>>> broke something)
>>>>>
>>>>> Hi,
>>>>>
>>>>> r302284 added an invalid check which breaks collating ranges:
>>>>>
>>>>> -if (table->__collate_load_error) {
>>>>> - (void)REQUIRE((uch)start <= (uch)finish, REG_ERANGE);
>>>>> +if (table->__collate_load_error || MB_CUR_MAX > 1) {
>>>>> + (void)REQUIRE(start <= finish, REG_ERANGE);
>>>>>
>>>>> The "MB_CUR_MAX > 1" is wrong, we should be doing proper comparison
>>>>> according to current locale's collation and not simply comparing the
>>>>> wchar_t values.
>>>>
>>>>
>>>>
>>>> After re-reading the specification I now see that what looked like a bug
>>>> is
>>>> actually an implementation choice, though the one that needs to be
>>>> documentated. I'll update the man page if anyone is willing to review
>>>> (and
>>>> commit) the changes.
>>>
>>>
>>> Can you point to the section of specification that indicates this is
>>> OK behavior? It doesn't seem desirable, but I see that GNU systems
>>> will operate in the same manner that we do now.
>>
>>
>> Here --
>> http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html:
>> ------------------------------------------------------------------------
>> In the POSIX locale, a range expression represents the set of collating
>> elements that fall between two elements in the collation sequence,
>> inclusive. In other locales, a range expression has unspecified behavior:
>> strictly conforming applications shall not rely on whether the range
>> expression is valid, or on the set of collating elements matched.
>> ------------------------------------------------------------------------
>>
>
> Thanks- our current behavior seems reasonable in that context.
>
>> I've tried to "fix" what I was seeing as well, and yes, everything outside
>> of ASCII is ugly, e.g. Cyrillic 'а-я' would match much more than you could
>> expect if you are doing lookups based on collation order (capital chars and
>> a lot of other symbols).
>>
>> So what we have currently looks the least evil to me:
>>
>> - non-collating ASCII lookups for any locale -- looking at the log for
>> regcomp.c there was an attempt to "fix" this, but it was reverted as
>> a lot of existing code relies on this;
>> - non-collating multi-byte locale lookups -- they will work for almost
>> all cases, and where they don't, well POSIX says it's undefined :D
>> - collating single-byte locale lookups for outside of ASCII range --
>> they make sense as collation order there doesn't seem to mix
>> small/caps/other characters together.
>>
>> What I think we need to do is document this as implementation choice in the
>> code and regex(3) "IMPLEMENTATION NOTES" so that another poor soul doesn't
>> come trying to fix it as I did :-)
>
> I agree with your assessment- such a patch would be welcomed,
> especially before I go and revise a bunch of this for clarification in
> a future libregex world.
Actually, it's broken even more than I thought:
$ echo 'TEST' | LC_ALL=en_US.ISO8859-1 grep '[a-z]'
TEST
That's a result of using collation lookup for singlebyte locales. Now I
just think that using collations for range expressions in *any* locale
is just plain wrong.
Another side effect of all this "sometimes non-collating" nonsense is
inability to deal with multibyte characters whose corresponding wide
character is in 128-255 range -- try adding 'µ' (\302\265, U+00B5) to
the pattern and observe a nice ~1GB core from grep after endless loop in
regcomp(). This is due to NC (I guess meaning "non-collating") being
defined as (CHAR_MAX - CHAR_MIN + 1) which is 256.
To sum the above, how about we drop the "non-collating" notion, and just
use binary wide character comparison everywhere?
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?2c9ebf81-c06a-13ed-9cf9-9b42a00c76ee>