From: Alejandro Colomar <alx.manpages@gmail.com>
To: GNU C Library <libc-alpha@sourceware.org>,
Siddhesh Poyarekar <siddhesh@gotplt.org>
Cc: наб <nabijaczleweli@nabijaczleweli.xyz>
Subject: regexec(3): REG_STARTEND is not documented
Date: Fri, 21 Apr 2023 02:45:00 +0200 [thread overview]
Message-ID: <0de87674-1b35-8dc8-7d2b-8dacd6b015ff@gmail.com> (raw)
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Hi Siddhesh,
It seems the glibc manual doesn't cover REG_STARTEND. We're having
some discussion about it, while we're improving the manual page, and
we have some slight disagreement about what are the constraints for
nmatch and pmatch when REG_STARTEND is specified.
Since this is a BSD extension, not in POSIX, we can't refer to the
standard. And since glibc doesn't document it, I can't know for
sure your intention.
I'm not sure how much we should rely on implementation details, and
if those will hold forever, or _FORTIFY_SOURCE and the like are
allowed to constrain some current details.
The discussion is in this thread, if you want to read it entirely:
<https://lore.kernel.org/linux-man/09bda4f5-ab6f-a369-ad36-0779dc3749b4@gmail.com/T/#m7dd7771072df3be97bc831f581dc7bfea684197d>
The question is:
If REG_STARTEND was specified _and_ REG_NOSUB was also specified,
regexec(3) will read from pmatch[0] and will effectively ignore
nmatch (the number of elements in pmatch[]), since it won't write
to pmatch[] at all.
Is the following call valid, or is it UB?
regmatch_t pmatch = {
.rm_so = string,
.rm_eo = string + 42, // Assume this offset is valid
};
regexec(preg, string, 0, pmatch, REG_NOSUB | REG_STARTEND);
How about this?
regexec(preg, string, 999, pmatch, REG_NOSUB | REG_STARTEND);
Current implementations will work, because nmatch is effectively
ignored. But is it intended to be this way, or just an implementation
detail?
Thanks!
Alex
--
<http://www.alejandro-colomar.es/>
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next reply other threads:[~2023-04-21 0:45 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-04-21 0:45 Alejandro Colomar [this message]
2023-04-21 1:07 ` Alejandro Colomar
2023-04-21 1:15 ` наб
2023-04-21 1:28 ` Alejandro Colomar
2023-04-21 1:41 ` наб
2023-04-21 1:47 ` Alejandro Colomar
2023-04-21 11:59 ` Siddhesh Poyarekar
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