How to debug an infinite loop in pdfLaTeX code

Question

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 
]{MyriadPro}
\begin{document}
\begin{equation}
\oiint  
\end{equation}
\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

Answer 1

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.