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-\section{Storing the program counter}
-\label{sec:fix-storing-pc}
-
-\begin{multicols}{2}
-
-The first issue I ran into is that of storing the program counter.
-Storing the program counter on the stack is something done commonly in many languages during a function call.
-
-\subsection{ARM code example}
-Usually, an offset to the actual program counter at the moment of the store instruction is stored,
-to allow for a branch after that instruction, and have the callee return to the address after that branch.
-The ARM architecture accommodates for this: an instruction that reads the program counter, actually reads
-	\enquote{the address of the current instruction plus 8}~\cite[A2.3]{armv7ar}.
-The following ARM assembly example illustrates this (\texttt{armstartup.s:540-2},~\cite{armrts}):
-
-\begin{minted}{ual}
-	str     pc,[sp,#-4]!
-	bl      init_clean
-	tst     r4,r4
-\end{minted}
-
-\begin{lrbox}{\ualbox}
-	\ual{[sp,#-4]!}
-\end{lrbox}
-
-Dummy addresses have been indicated in comments.
-When execution arrives at \ual{0x20}, the program counter is set to \ual{0x20}.
-Per the above documentation, \ual{str} stores \ual{0x20+8} on the stack%
-	\footnote{\usebox{\ualbox}
-		indicates that the stack pointer should be decreased by four before storing the program counter on the stack.
-		It has nothing to do with the 8 offset that is added to the program counter itself.}.
-The processor branches to \ual{init_clean},
-	which loads the value from the stack back into the program counter to return to the caller.
-The program counter is then \ual{0x28}.
-For the next instruction cycle, the \ual{tst} command is executed.
-
-\subsection{Adapting for Thumb-2}
-There are two reasons why the above cannot be used in Thumb-2 code.
-
-First, \ual{pc} is not allowed as the first operand to a \ual{str} instruction.
-Hence, we need to first move \ual{pc} to an auxiliary register, and then push that on the stack.
-We then get:
-
-\begin{minted}{ual}
-	add     lr,pc,#9
-	str     lr,[sp,#-4]!
-	bl      init_clean
-	tst     r4,r4
-\end{minted}
-
-We store the value \ual{0x2d}.
-This address points to the \ual{tst} instruction as before, with the LSB set to 1 to indicate Thumb mode.
-
-The second problem we meet is that the instruction to store the program counter may be halfword-aligned rather than word-aligned.
-We saw above that a read of the program counter in ARM mode reads as PC+8.
-In Thumb mode this is more complicated.
-In this case, we 
-	\enquote{[r]ead the word-aligned PC value, that is,
-		the address of the current instruction + 4,
-		with bits [1:0] forced to zero}~\cite[A5.1.2]{armv7m}.
-This means that when the \ual{add} instruction above is at \ual{0x22},
-	we will still store \ual{0x2d} on the stack,
-	since the word-aligned program counter is \ual{0x20} as before.
-However, in this case \ual{bl} is located at \ual{0x2a}, and since this is a 32 bits instruction we point to the middle of that instruction.
-
-In hand-written code, we can solve this by adding labels for the addresses we want to store on the stack.
-In generated code, we need to keep track of the current alignment and add either 9 or 11 to the read program counter.
-
-\subsection{Other solutions}
-Another solution than the one we present here is the use of the link register.
-Branch instructions as \ual{bl} store the address of the next instruction in the link register.
-We could therefore imagine a setup where the callee gets the return address from that register rather than from the stack.
-This is the approach taken by GCC.
-The code of a typical C subroutine starts with \ual{push {r7,lr}} and ends with \ual{pop {r7,pc}}.
-
-When generating code for a functional language, this is not easily done due to tail recursion.
-It is an easier solution to have the caller responsible for storing the return address,
-	which is why this approach is taken in Clean's ARM code generator\cite{armcg}
-	and why I continue along those lines.
-
-\subsection{Complexity analysis}
-To be done. %TODO
-
-For every occurrence: +1 word code size;
-for every function call: +1 instruction.
-
-\end{multicols}