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Index > Windows > byte register name of dword register name esi

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Sandurr



Joined: 20 Oct 2007
Posts: 2
Sandurr
Hello,

What is the byte register name of esi?

Like dl is for edx

In OllyDbg
Post 27 Oct 2007, 19:06
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Xorpd!



Joined: 21 Dec 2006
Posts: 161
Xorpd!
sil. That said, I thought that OllyDbg was 32-bit software and so couldn't access it directly.
Post 27 Oct 2007, 19:47
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vid
Verbosity in development


Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia
vid
there is no way to access it directly in 32bit code. only in 64bit code
Post 27 Oct 2007, 19:50
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f0dder



Joined: 19 Feb 2004
Posts: 3170
Location: Denmark
f0dder
...and in 64bit mode, you can only access the lowest part, right? (ie, no AH/BH/CH/DH).
Post 28 Oct 2007, 00:52
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vid
Verbosity in development


Joined: 05 Sep 2003
Posts: 7105
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vid
yup
Post 28 Oct 2007, 01:02
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Xorpd!



Joined: 21 Dec 2006
Posts: 161
Xorpd!
I would say "yup" to one interpretation of f0dder's question, which is to ask whether there is no 8-bit register corresponding to bits 8:15 of RSP/RBP/RSI/RDI.

I would say "nope" to another interpretation, which is to ask whether the AH/CH/DH/BH registers are not directly addressible in 64-bit mode.

That's a lot of negatives above, so let me summarize by saying that in 64-bit mode if an instruction has a REX prefix it may address registers al/cl/dl/bl/spl/bpl/sil/dil/r8l/r9l/r10l/r11l/r12l/r13l/r14l/r15l. If an instruction has no REX prefix it may address registers al/cl/dl/bl/ah/ch/dh/bh.
Post 28 Oct 2007, 01:30
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vid
Verbosity in development


Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia
vid
you are right, sorry.
Post 28 Oct 2007, 01:42
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f0dder



Joined: 19 Feb 2004
Posts: 3170
Location: Denmark
f0dder
Thanks for the clarification Smile
Post 28 Oct 2007, 14:06
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