How to debug an infinite loop in pdfLaTeX code

I have some code which crashes when loading the myriadpro package and loading in the document only the symbol \oiint

\documentclass[]{scrbook}
\usepackage[T1]{fontenc}
\usepackage{amsmath} %
\usepackage[%
onlytext,    % only change the text fonts
sansmath,    % provide math version sans and sansbold
\begin{document}
$$\oiint$$
\end{document}


Note that the MyriadPro package and the fonts are not available on ctan.

Any idea how to find out why pdflatex crashes? (CPU is 100%)

EDIT: pdftex version is: This is pdfTeX, Version 3.1415926-2.3-1.40.12 (MiKTeX 2.9) (preloaded format=pdflatex 2011.12.12)

EDIT2: The author of the MyriadPro package confirmed, that this endless loop happens when "Myriad is loaded with onlytext and sansmath and in the document a math command is called in the mathversion normal, which is not defined by MyriadPro (\oiint)."

EDIT3: Here the code of the endless loop, it is repeated endlessly with the last number increasing. However, I have not idea where the error comes from. Anyway I now know a bit more how to debug such an error and can provide a better error description to the author of the package.

is@range #1-#2@nil ->if >#2expandafter check@single else expandafter check@rang
e fi
#1<-5
#2<->
{if: (level 6) entered on line 10}
{true}
{expandafter}
{else: if (level 6) entered on line 10}
{fi: if (level 6) entered on line 10}

check@single #1>#2<#3@nnil ->def reserved@f {extract@rangefontinfo <#3@nnil }if
dim f@size p@ =#1p@ set@simple@size@args #2<#3@nnil execute@size@function sizef
n@info ifx external@font @empty else let reserved@f @empty fi fi reserved@f
#1<-5
#2<-
#3<-6><7><8><9><10><12>gen*cmr<10.95>cmr10<14.4>cmr12<17.28><20.74><24.88>cmr17
<-*>@nil <
{def}
{changing reserved@f=relax}
{into reserved@f=macro:->extract@rangefontinfo <6><7><8ETC.}
{ifdim: (level 6) entered on line 10}

f@size ->8
{false}
{fi: ifdim (level 6) entered on line 10}

reserved@f ->extract@rangefontinfo <6><7><8><9><10><12>gen*cmr<10.95>cmr10<14.4
>cmr12<17.28><20.74><24.88>cmr17<-*>@nil <@nnil

extract@rangefontinfo #1<#2>->is@range #2->@nil #2>
#1<-
#2<-6

-
Could you provide a link for the package (for those people who have the fonts available)? It would also be useful to specify the exact version of pdfTeX we are talking about. –  Joseph Wright Dec 23 '11 at 15:54
What's the meaning of "crashes" in this particular case? –  egreg Dec 23 '11 at 16:06
The required packages are: github.com/sebschub/MdSymbol github.com/sebschub/FontPro Crash means that it stops and CPU is 100%. log files ends where pdflatex stopped. –  Matthias Pospiech Dec 23 '11 at 16:28
It's most likely not crashing but in an endless loop. Add a \tracingall to your document (after \begin{document}) and study the output/log file.