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Comment on instructions in $pcrel_hi/lo examples

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John Winans 2021-03-05 14:08:17 -06:00
parent adbcd27a43
commit 642a664e27
1 changed files with 8 additions and 7 deletions
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13
book/programs/chapter.tex
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@ -589,7 +589,7 @@ Examples of using the \verb@auipc@ \& \verb@addi@ together with \verb@%pcrel_hi(
{\small
\begin{verbatim}
xxx: auipc t1,%pcrel_hi(yyy) // (yyy-xxx) >>U 12) + ((yyy-xxx) & 0x00000800 ? 1 : 0)
xxx: auipc t1,%pcrel_hi(yyy) // (yyy-.) >>U 12) + ((yyy-.) & 0x00000800 ? 1 : 0)
addi t1,t1,%pcrel_lo(xxx) // ((yyy-xxx) & 0x00000fff)
...
yyy: // the address: yyy is saved into t1 above
@ -598,14 +598,15 @@ yyy: // the address: yyy is saved into t1 above
}
Things like this are legal:
Referencing the same \verb@%pcrel_hi@ in multiple subsequent uses of \verb@%pcrel_lo@ is legal:
{\small
\begin{verbatim}
label: auipc t1,%pcrel_hi(symbol)
addi t2,t1,%pcrel_lo(label)
addi t3,t1,%pcrel_lo(label)
lw t4,%pcrel_lo(label)(t1)
sw t5,%pcrel_lo(label)(t1)
addi t2,t1,%pcrel_lo(label) // t2 = symbol
addi t3,t1,%pcrel_lo(label) // t3 = symbol
lw t4,%pcrel_lo(label)(t1) // t4 = fetch value from memory at 'symbol'
addi t4,t4,123 // t4 = t4 + 123
sw t4,%pcrel_lo(label)(t1) // store t4 back into memory at 'symbol'
\end{verbatim}
}