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Re: Infinite loop generating QEMU docs after upgrade to Perl 5.28.0


From: Gavin Smith
Subject: Re: Infinite loop generating QEMU docs after upgrade to Perl 5.28.0
Date: Thu, 28 Jun 2018 23:40:14 +0100

On Wed, Jun 27, 2018 at 1:46 PM, Melvin Mawhin
<address@hidden> wrote:
> Since upgrading to perl 5.28 in slackware-current we ran into a bug while
> generating documentation for qemu
>
> The version number of Texinfo and the program(s) or manual(s) involved.
> Texinfo 6.5 / Qemu 2.12.0 (docs) / Perl 5.28.0
> The contents of any input files necessary to reproduce the bug.
> The Qemu sources contain the document files


> Precisely how you ran any program(s) involved.
> I ran configure and make. The command causing issues is:
> LC_ALL=C makeinfo --no-split --number-sections -I docs -I . -I .
> --no-headers --plaintext qemu-doc.texi -o qemu-doc.txt

I have downloaded and installed Perl 5.28 on my computer but haven't
been able to reproduce the bug yet. I downloaded the qemu sources. I
had to build qemu to get all the documentation files (otherwise files
were missing) but they appeared to build OK:

  GEN     qemu-doc.txt
Unescaped left brace in regex is deprecated here (and will be fatal in
Perl 5.32), passed through in regex; marked by <-- HERE in
m/^\s+@([[:alnum:]][[:alnum:]\-]*)({ <-- HERE })?\s*/ at
/home/g/local/share/texinfo/Texinfo/Parser.pm line 5481.
Unescaped left brace in regex is deprecated here (and will be fatal in
Perl 5.32), passed through in regex; marked by <-- HERE in
m/^\s+@([[:alnum:]][[:alnum:]\-]*)({ <-- HERE
})?\s*(\@(c|comment)((\@|\s+).*)?)?/ at
/home/g/local/share/texinfo/Texinfo/Parser.pm line 5485.
  GEN     qemu.1
  GEN     qemu-img.1
  GEN     qemu-nbd.8

I didn't let the build finish but this appears to be enough to show
the problem didn't occur. Afterwards, I ran

LC_ALL=C makeinfo --no-split --number-sections -I docs -I . -I .
--no-headers --plaintext qemu-doc.texi -o qemu-doc.txt

in the qemu sources and this also worked without any problems.

It would help if you could email the complete set of *.texi files
needed to reproduce the error so that anybody working on it does not
have to deal with downloading or building qemu.

The way that I would start with debugging this, assuming I could
reproduce the bug in the first place (which I can't so far), is to run
makeinfo to get it to hang, and then attach to the running perl
process with gdb. E.g.

function attach () {
        gdb $1 `pgrep $1`
}
attach perl

Since we have established the problem occurs in the XS extensions to
the perl executable, it should be straightforward then to step through
the code with gdb and see where the infinite loop occurs.



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