
It isn't really a reverse as it is the order the items are collected, it is makeindex that does the reversal to make the normal index.
\documentclass{article}
\usepackage{makeidx}
\makeindex
\begin{document}
\section{main}
aaa\index{ho} bbb\index{foo} cc\index{grrr}
\clearpage
aaa\index{ho} bbb\index{foo} cc\index{grrr}
aaa\index{zho} bbb\index{zfoo} cc\index{zgrrr}
\clearpage
aaa\index{bho} bbb\index{foo} cc\index{grrr}
{\clearpage
\section*{xedni}
\makeatletter
\immediate\closeout\@indexfile
\def\lastp{}
\def\indexentry#1#2{%
\def\thisp{#2}%
\ifx\thisp\lastp
\unskip, %
\else
\let\lastp\thisp
\item[#2: ]%
\fi
#1}
\begin{itemize}
\InputIfFileExists{\jobname.idx}{}{}
\end{itemize}
}
\printindex
\end{document}
\index{...}entry method? if so, it should be possible to do something "sensible" with the.idxfile(s) that are generated automatically -- they're already in page number order. i don't know that anyone has done such a thing, but i look into such files all the time to check the input when problems arise. – barbara beeton Jun 12 '13 at 17:50