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Add leading zeros to literals to eliminate sign confusion

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John Winans 2021-03-05 13:53:45 -06:00
parent 6e0bb98500
commit adbcd27a43
1 changed files with 13 additions and 13 deletions
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26
book/programs/chapter.tex
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@ -365,26 +365,26 @@ Introduce and present subroutines but not nesting until introduce stack operatio
{\small
\begin{verbatim}
li rd,constant lui rd,(constant >>U 12)+(constant & 0x00000800 ? 1 : 0)
addi rd,rd,(constant & 0xfff)
addi rd,rd,(constant & 0x00000fff)
la rd,label
auipc rd,((label-.) >>U 12) + ((label-.) & 0x00000800 ? 1 : 0)
addi rd,rd,((label-(.-4)) & 0xfff)
addi rd,rd,((label-(.-4)) & 0x00000fff)
l{b|h|w} rd,label
auipc rd,((label-.) >>U 12) + ((label-.) & 0x00000800 ? 1 : 0)
l{b|h|w} rd,((label-(.-4)) & 0xfff)(rd)
l{b|h|w} rd,((label-(.-4)) & 0x00000fff)(rd)
s{b|h|w} rd,label,rt # rt used as a temp reg for the operation (default=x6)
auipc rt,((label-.) >>U 12) + ((label-.) & 0x00000800 ? 1 : 0)
s{b|h|w} rd,((label-(.-4)) & 0xfff)(rt)
s{b|h|w} rd,((label-(.-4)) & 0x00000fff)(rt)
call label auipc x1,((label-.) >>U 12) + ((label-.) & 0x00000800 ? 1 : 0)
jalr x1,((label-(.-4)) & 0xfff)(x1)
jalr x1,((label-(.-4)) & 0x00000fff)(x1)
tail label,rt # rt used as a temp reg for the operation (default=x6)
auipc rt,((label-.) >>U 12) + ((label-.) & 0x00000800 ? 1 : 0)
jalr x0,((label-(.-4)) & 0xfff)(rt)
jalr x0,((label-(.-4)) & 0x00000fff)(rt)
mv rd,rs addi rd,rs,0
@ -427,7 +427,7 @@ To remedy this problem, the value used in the {\tt lui} instruction can altered
instruction:
{\small
\begin{verbatim}
lui x5,0x12346 // x5 = 0x12346000 (note this is 0x12345 + 1)
lui x5,0x12346 // x5 = 0x12346000 (note: this is 0x12345000 + 0x1000)
addi x5,x5,0x800 // x5 = 0x12346000 + sx(0x800) = 0x12346000 + 0xfffff800 = 0x12345800
\end{verbatim}
}
@ -481,7 +481,7 @@ The \verb@la@ instruction here will expand into:
{\small
\begin{verbatim}
00010040 auipc x10,((var1-.) >>U 12) + ((var1-.) & 0x00000800 ? 1 : 0)
00010044 addi x10,x10,((var1-(.-4)) & 0xfff)
00010044 addi x10,x10,((var1-(.-4)) & 0x00000fff)
\end{verbatim}
}
@ -498,14 +498,14 @@ Therefore the expanded pseudoinstruction example will become:
{\small
\begin{verbatim}
00010040 auipc x10,((0x00010900-0x00010040) >>U 12) + ((0x00010900-0x00010040) & 0x00000800 ? 1 : 0)
00010044 addi x10,x10,((0x00010900-(0x00010044-4)) & 0xfff) # note the extra -4 here!
00010044 addi x10,x10,((0x00010900-(0x00010044-4)) & 0x00000fff) # note the extra -4 here!
\end{verbatim}
}
After performing the subtractions, it will reduce to this:
{\small
\begin{verbatim}
00010040 auipc x10,(0x000008c0 >>U 12) + ((0x000008c0) & 0x00000800 ? 1 : 0)
00010044 addi x10,x10,(0x000008c0 & 0xfff)
00010044 addi x10,x10,(0x000008c0 & 0x00000fff)
\end{verbatim}
}
Continuing to reduce the math operations we get:
@ -546,7 +546,7 @@ To refer to an absolute value, the following operators can be used:
{\small
\begin{verbatim}
%hi(constant) // becomes: (constant >>U 12)+(constant & 0x00000800 ? 1 : 0)
%lo(constant) // becomes: (constant & 0xfff)
%lo(constant) // becomes: (constant & 0x00000fff)
\end{verbatim}
}
@ -567,7 +567,7 @@ The following can be used for PC-relative addresses:
{\small
\begin{verbatim}
%pcrel_hi(symbol) // becomes: ((symbol-.) >>U 12) + ((symbol-.) & 0x00000800 ? 1 : 0)
%pcrel_lo(lab) // becomes: ((symbol-lab) & 0xfff)
%pcrel_lo(lab) // becomes: ((symbol-lab) & 0x00000fff)
\end{verbatim}
}
@ -590,7 +590,7 @@ 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)
addi t1,t1,%pcrel_lo(xxx) // ((yyy-xxx) & 0xfff)
addi t1,t1,%pcrel_lo(xxx) // ((yyy-xxx) & 0x00000fff)
...
yyy: // the address: yyy is saved into t1 above
...