How do I embed a listing in a tabular?

You can define a \lstnewenvironment with the adjustments for the specific case.

The option here in \lstset can also be given as options to tabularlstlisting or changed locally with

\begin{tabularlstlisting}[<options>]

Full example:

\documentclass{article}
\thispagestyle{empty}
\usepackage{listings}

\lstnewenvironment{tabularlstlisting}[1][]
 {%
  \lstset{aboveskip=-1.3ex,belowskip=-3.5ex,#1}%
 }
 {}

\begin{document}

\lstset{numbers=none, language={[x86masm]Assembler}, basicstyle=\linespread{0.8}\footnotesize}

\begin{tabular}{l|p{6cm}|p{4cm}}
Fact name
 & Description
 & Assembly code example\\
\hline
hello & Instruction  in  allocates  bytes of memory for the object blah blah blah. &
\begin{tabularlstlisting}
push 28h
call operator new
\end{tabularlstlisting}
\\
\hline
\end{tabular}

\bigskip

\begin{tabular}{l|p{6cm}|p{4cm}}
Fact name
 & Description
 & Assembly code example\\
\hline
hello & Instruction  in  allocates  bytes of memory for the object blah blah blah. &
\begin{tabularlstlisting}
push 28h
call operator new
push 28h
call operator new
push 28h
call operator new
push 28h
call operator new
\end{tabularlstlisting}
\\
\hline
\end{tabular}

\end{document}

You can use a \vskip to adjust placement. I found that \baselineskip+\smallskipamount gave ok result. As demonstrated by the added rule to visualize things.

\documentclass{article}
\thispagestyle{empty}
\usepackage{listings}

\begin{document}

\begin{table*}[h]
  \lstset{numbers=none, language={[x86masm]Assembler},
    basicstyle=%\linespread{0.8}
               %\footnotesize
  }
  \begin{tabular}{l|p{6cm}|p{6cm}}
    Fact name
    & Description
    & Assembly code example\\
    \hline
    hello & Instruction\rlap{\rule{10cm}{0.4pt}}  in  allocates  bytes of memory for the object blah blah blah.
    &
\vskip-\baselineskip
\vskip-\smallskipamount
\begin{lstlisting}
push 28h
call operator new
\end{lstlisting}
\kern-\baselineskip
  \end{tabular}
  \caption{Attempt two.}
\end{table*}

\end{document}

A solution with a \raisebox of the relevant value (the default value of the aboveskip key is \medskipamount):

\documentclass{article}
\thispagestyle{empty}
\usepackage{listings}
\usepackage{array}

\begin{document}

\begin{table*}[!h]\setlength{\extrarowheight}{3pt}
  %\lstset{numbers=none, language={[x86masm]Assembler}, basicstyle=\linespread{0.8}\footnotesize}
\setlength{\tabcolsep}{4pt}
\centering
  \begin{tabular}{l|p{6cm}|>{\vspace*{-\dimexpr \baselineskip+0.55ex}\arraybackslash}l}
    Fact name
    & Description
    & Assembly code example\\[1ex]
    \hline
    hello & Instruction in allocates bytes of memory for the object blah blah blah.
    &
\raisebox{-\medskipamount}{
\hspace{-1em}\begin{lstlisting}^^J
push 28h^^J
call operator new
\end{lstlisting}}\\%
  \end{tabular}
  \caption{Attempt two.}
\end{table*}

\end{document}