* [musl] Different results with regex.h between Musl and Libc
@ 2024-06-10 5:38 Nigel Kukard
2024-06-10 11:47 ` [musl] " Valery Ushakov
0 siblings, 1 reply; 4+ messages in thread
From: Nigel Kukard @ 2024-06-10 5:38 UTC (permalink / raw)
To: musl
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Hi there,
I'm wondering if someone could possibly point out what I'm doing wrong here.
I tried searching the mailing list for similar topics, I found some
relating to POSIX regex but none that really dealt with this issue with
extended regex. I also didn't find anything really addressing this on
https://wiki.musl-libc.org/functional-differences-from-glibc.html.
If I missed something I'm terribly sorry.
Musl output (Alpine 3.20), musl-1.2.5-r1...
The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
Match 0: 37
Match 1:
Match 2: 37
Glibc output (ArchLinux), glibc 2.39+r52+gf8e4623421-1...
The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
Match 0: 37
Match 1: 37
Match 2:
Test code...
/*--------------------*/
#include <stdio.h>
#include <regex.h>
int main() {
const char *pattern = "^([0-9]*)?\\.?([0-9]*)?$";
const char *input = "37";
regex_t regex;
regmatch_t matches[3];
int ret;
ret = regcomp(®ex, pattern, REG_EXTENDED);
if (ret) {
fprintf(stderr, "Could not compile regex\n");
return 1;
}
ret = regexec(®ex, input, 3, matches, 0);
if (!ret) {
printf("The input '%s' matches the pattern '%s'\n", input,
pattern);
for (int i = 0; i < 3; i++) {
if (matches[i].rm_so != -1) {
printf("Match %d: %.*s\n", i, matches[i].rm_eo -
matches[i].rm_so, input + matches[i].rm_so);
}
}
} else if (ret == REG_NOMATCH) {
printf("The input '%s' does not match the pattern '%s'\n",
input, pattern);
} else {
char msgbuf[100];
regerror(ret, ®ex, msgbuf, sizeof(msgbuf));
fprintf(stderr, "Regex match failed: %s\n", msgbuf);
return 1;
}
regfree(®ex);
return 0;
}
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^ permalink raw reply [flat|nested] 4+ messages in thread
* [musl] Re: Different results with regex.h between Musl and Libc
2024-06-10 5:38 [musl] Different results with regex.h between Musl and Libc Nigel Kukard
@ 2024-06-10 11:47 ` Valery Ushakov
2024-06-10 15:56 ` Rich Felker
0 siblings, 1 reply; 4+ messages in thread
From: Valery Ushakov @ 2024-06-10 11:47 UTC (permalink / raw)
To: musl
On Mon, Jun 10, 2024 at 05:38:36 +0000, Nigel Kukard wrote:
> Musl output (Alpine 3.20), musl-1.2.5-r1...
>
> The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
> Match 0: 37
> Match 1:
> Match 2: 37
>
> Glibc output (ArchLinux), glibc 2.39+r52+gf8e4623421-1...
>
> The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
> Match 0: 37
> Match 1: 37
> Match 2:
I'm not sure what POSIX requires here. The closest I can find after
skimming through "9. Regular Expressions" is 9.4.6 that ends with:
An ERE matching a single character repeated by an '*', '?', or an
interval expression shall not match a null expression unless this is
the only match for the repetition or it is necessary to satisfy the
exact or minimum number of occurrences for the interval expression.
https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04_06
I'm not sure what to read into the absense of the usual "or an ERE
enclosed in parentheses" chorus here.
> printf("Match %d: %.*s\n", i, matches[i].rm_eo - matches[i].rm_so, input + matches[i].rm_so);
Nit-pick: regoff_t may be wider than int (expected by '*'). E.g. your
test program prints nothing for all those %.* on NetBSD/macppc (with
the appropriate cast it prints 37/37/<empty>), as regoff_t is 64-bit
(very old posix required regoff_t to be at least as wide as off_t).
It will probably crash on a little-endian 32-bit NetBSD system, b/c
the zero MSW of a 64-bit regoff_t will be interpreted as the argument
for %s.
-uwe
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [musl] Re: Different results with regex.h between Musl and Libc
2024-06-10 11:47 ` [musl] " Valery Ushakov
@ 2024-06-10 15:56 ` Rich Felker
2024-06-10 17:57 ` Valery Ushakov
0 siblings, 1 reply; 4+ messages in thread
From: Rich Felker @ 2024-06-10 15:56 UTC (permalink / raw)
To: Valery Ushakov; +Cc: musl, Nigel Kukard
On Mon, Jun 10, 2024 at 02:47:04PM +0300, Valery Ushakov wrote:
> On Mon, Jun 10, 2024 at 05:38:36 +0000, Nigel Kukard wrote:
>
> > Musl output (Alpine 3.20), musl-1.2.5-r1...
> >
> > The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
> > Match 0: 37
> > Match 1:
> > Match 2: 37
> >
> > Glibc output (ArchLinux), glibc 2.39+r52+gf8e4623421-1...
> >
> > The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
> > Match 0: 37
> > Match 1: 37
> > Match 2:
>
> I'm not sure what POSIX requires here. The closest I can find after
> skimming through "9. Regular Expressions" is 9.4.6 that ends with:
>
> An ERE matching a single character repeated by an '*', '?', or an
> interval expression shall not match a null expression unless this is
> the only match for the repetition or it is necessary to satisfy the
> exact or minimum number of occurrences for the interval expression.
>
> https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04_06
>
> I'm not sure what to read into the absense of the usual "or an ERE
> enclosed in parentheses" chorus here.
This looks like a bug. The general requirement (from memory; I don't
have the spec in front of me now) is that each subexpression, in order
from the beginning of the regex, matches the maximal-length input it
can, subject to the overall constraint that the entire regex match the
earliest (first priority) and maximal length (second priority) input
it can.
I guess we need to dig into why this is happening, ensure it's
actually incorrect, and figure out how to fix it...
Rich
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [musl] Re: Different results with regex.h between Musl and Libc
2024-06-10 15:56 ` Rich Felker
@ 2024-06-10 17:57 ` Valery Ushakov
0 siblings, 0 replies; 4+ messages in thread
From: Valery Ushakov @ 2024-06-10 17:57 UTC (permalink / raw)
To: Rich Felker; +Cc: musl, Nigel Kukard
On Mon, Jun 10, 2024 at 11:56:14 -0400, Rich Felker wrote:
> On Mon, Jun 10, 2024 at 02:47:04PM +0300, Valery Ushakov wrote:
> > On Mon, Jun 10, 2024 at 05:38:36 +0000, Nigel Kukard wrote:
> >
> > > Musl output (Alpine 3.20), musl-1.2.5-r1...
> > >
> > > The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
> > > Match 0: 37
> > > Match 1:
> > > Match 2: 37
> > >
> > > Glibc output (ArchLinux), glibc 2.39+r52+gf8e4623421-1...
> > >
> > > The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
> > > Match 0: 37
> > > Match 1: 37
> > > Match 2:
> >
> > I'm not sure what POSIX requires here. The closest I can find after
> > skimming through "9. Regular Expressions" is 9.4.6 that ends with:
> >
> > An ERE matching a single character repeated by an '*', '?', or an
> > interval expression shall not match a null expression unless this is
> > the only match for the repetition or it is necessary to satisfy the
> > exact or minimum number of occurrences for the interval expression.
> >
> > https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04_06
> >
> > I'm not sure what to read into the absense of the usual "or an ERE
> > enclosed in parentheses" chorus here.
>
> This looks like a bug. The general requirement (from memory; I don't
> have the spec in front of me now) is that each subexpression, in order
> from the beginning of the regex, matches the maximal-length input it
> can, subject to the overall constraint that the entire regex match the
> earliest (first priority) and maximal length (second priority) input
> it can.
>
> I guess we need to dig into why this is happening, ensure it's
> actually incorrect, and figure out how to fix it...
You are right, 9.1 Regular Expression Definitions has under "matched":
Consistent with the whole match being the longest of the leftmost
matches, each subpattern, from left to right, shall match the
longest possible string. For this purpose, a null string shall be
considered to be longer than no match at all. For example,
matching the BRE "\(.*\).*" against "abcdef", the subexpression
"(\1)" is "abcdef", and matching the BRE "\(a*\)*" against "bc",
the subexpression "(\1)" is the null string.
-uwe
^ permalink raw reply [flat|nested] 4+ messages in thread
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2024-06-10 5:38 [musl] Different results with regex.h between Musl and Libc Nigel Kukard
2024-06-10 11:47 ` [musl] " Valery Ushakov
2024-06-10 15:56 ` Rich Felker
2024-06-10 17:57 ` Valery Ushakov
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