bug#27838: grep error: "regexec.c:1375: pop_fail_stack: Assertion `num >= 0' failed."

[Paul Eggert]

Thanks, that is due to an already known bug in glibc; see:

https://sourceware.org/bugzilla/show_bug.cgi?id=18986
https://debbugs.gnu.org/21513

To work around the problem with grep, use './configure --with-included-regex' 
when building grep, or encourage your upstream distributor to do so (or better 
yet, to fix glibc). You might also follow up on the glibc bug report to mention 
that the problem affects you too.

In the meantime I installed the attached patch, to add your test case to grep's 
test suite. The test is expected to fail if glibc regex is used.

0001-tests-add-Bug-27838-test-case.patch
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