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53 lines
3.1 KiB
TeX
53 lines
3.1 KiB
TeX
\newpage
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\subsection{The Stack}
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In the below two, we can do this with $x = 1, 2, 4, 8$, each corresponding to a size prefix that is set with \texttt{X}
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\bi{Stack push} \texttt{pushX src}: Fetch operand at \texttt{src}, decrement \texttt{\%rsp} by $x$, then writes the operand at address of \texttt{\%rsp}
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\bi{Stack pop} \texttt{popX dest}: Fetch operand at address of \texttt{\%rsp}, increment \texttt{\%rsp} by $x$, then writes the operand into \texttt{dest}
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\content{Procedure call / return} Use \texttt{call LABEL}. This pushes return label to the stack and jumps to the LABEL.
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After this instruction, we also may use the \texttt{pushX} instruction to store further registers.
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Just remember to pop in the correct order with the correct size again!
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The \texttt{ret} instruction is the return instruction and it will jump back to the caller and execution will continue there.
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\subsubsection{Calling Conventions}
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The callee is the function that is called and the caller is the code / function that calls the function.
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\begin{itemize}
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\item \texttt{\%rax} and \texttt{\%eax} can be used without first saving (usually used as return)
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\item Argument registers are caller saved (or not if not needed again)
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\item \texttt{\%rsp} should not be modified anyway
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\item \texttt{\%rbp} is callee saved and is used as frame pointer (usually set to equal \texttt{\%rsp} at start of procedure and can be used to access elements of the frame
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(as it should not change during execution of the function and should always point to the start of the frame))
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\end{itemize}
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\begin{multicols}{2}
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\begin{tables}{ll}{Name & Description}
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\texttt{\%rax} & Return value, \#variable args \\
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\texttt{\%rbx} & Base pointer, Callee saved \\
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\texttt{\%rcx} & Argument 4 \\
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\texttt{\%rdx} & Argument 3 (and return 2) \\
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\texttt{\%rsi} & Argument 2 \\
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\texttt{\%rdi} & Argument 1 \\
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\texttt{\%rsp} & Stack pointer \\
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\texttt{\%rbp} & Frame pointer, Callee saved \\
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\end{tables}
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\begin{tables}{ll}{Name & Description}
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\texttt{\%r8} & Argument 5 \\
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\texttt{\%r9} & Argument 6 \\
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\texttt{\%r10} & Static chain pointer \\
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\texttt{\%r11} & Temporary \\
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\texttt{\%r12} & Callee saved \\
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\texttt{\%r13} & Callee saved \\
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\texttt{\%r14} & Callee saved \\
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\texttt{\%r15} & GOT pointer, callee saved \\
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\end{tables}
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\end{multicols}
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If we have more than 6 arguments to be passed, we can use the stack for this.
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If we can do all accesses to the stack relative to the stack pointer, we do not need to
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update \texttt{\%rbp} and not even \texttt{\%rbx}, or we can use it for other purposes.
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We can also allocate the entire stack frame immediately by incrementing the stack pointer to the final position and then store data relative to it.
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To deallocate a stack frame, simply increment the stack pointer.
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