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[SPCA] Finish stack, data type compilation details

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Janis Hutz
2026-01-12 12:02:53 +01:00
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semester3/spca/parts/00_asm/01_syntax/01_registers.tex Normal file
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\subsubsection{Registers}
\texttt{x86} assembly is a bit particular with register naming (register names all start in \%).
The initial 16-bit version of \texttt{x86} had the following registers (sub registers are registers that can be used to access the high
(\texttt{h} suffix) or low (\texttt{l} suffix) half of the register. Only registers ending in \texttt{x} feature these sub registers.
They, as well as \texttt{\%si} and \texttt{\%di} are general purpose):
\begin{tables}{lll}{Name & Sub-registers & Description}
\texttt{\%ax} & \texttt{\%ah}, \texttt{\%al} & accumulate \\
\texttt{\%cx} & \texttt{\%ch}, \texttt{\%cl} & counter \\
\texttt{\%dx} & \texttt{\%dh}, \texttt{\%dl} & data \\
\texttt{\%bx} & \texttt{\%bh}, \texttt{\%bl} & base \\
\texttt{\%si} & - & Source index \\
\texttt{\%di} & - & Destination index \\
\hline
\texttt{\%sp} & - & Stack pointer \\
\texttt{\%bp} & - & Base pointer \\
\texttt{\%ip} & - & Instruction pointer \\
\texttt{\%sr} & - & Status (flags) \\
\end{tables}
When the architecture was extended to 32-bit, all registers previously available were retained and a 32 bit version of each was introduced with the prefix \texttt{e}.
In other words, any 16 bit code would still work as previously, as e.g. the \texttt{\%ax} register was simply now the lower 16 bits of the \texttt{\%eax} register.
The same happened again when extending to 64-bit, only this time the \texttt{r} prefix was used.
So, the register \texttt{\$eax} was now the lower 32 bits of \texttt{\%rax}.
Additionally, the following registers are also available, with \texttt{X} to be substituted with 8 through 15: \texttt{\%rX} and the lower 32 bits \texttt{\%rXd}