Re: address in DLL
Tim Roberts wrote:
"Ben Voigt [C++ MVP]" <rbv@nospam.nospam> wrote:
Tim Roberts wrote:
You have already shown that you know how to disassemble code in the
debugger. That is sufficient for Ben's demonstration.
True, but... you need to disassemble the code as it exists in the
DLL before relocation/fixups are processed by the loader. Visual
Studio by default shows you the disassembly of the loaded module,
already modified by the loader.
That doesn't matter one bit for the current question. He's trying to
establish whether jumps and calls are relative or absolute. If it
was an absolute call before the fix-up, it will be an absolute call
after the fixup.
Well, mostly yes. But I think he's not comparing absolute to relative, but
absolute to (computed/indexed) because he's been told that on some OSes the
library load address is placed in a register and used to calculate the
position of code at the call site (thus obviating the need for
copy-on-write).
And yes, this difference would be preserved by the loader. But you really
have to see the disassembly before fixup to understand how rebasing and
copy-on-write interact. After all, one hardly needs a preferred load
address at all, the loader could fixup the references always. But that
would be inefficient in terms both of memory (no sharing) and CPU time
(processing fixup table more often).
Relative calls and jumps don't need fixups.
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