Re: Arithmetic overflow checking
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On Thu, 7 Jul 2011, rop rop wrote:
On Jul 6, 11:32?pm, Tom Anderson <t...@urchin.earth.li> wrote:
Modding the JVM is a non-starter for a few reasons...
Could you just elaborate on this, please... what is the main-problem
with actually patching the JVM? Why is it so hard?
It would involve modifying a bytecode interpreter and two just-in-time
compilers, all three highly developed instances of their species, and all
written in C++. How much do you know about interpreters and compilers, and
how is your C++? I am a good Java programmer, but that task would be way
beyond me.
Without having looked into the source-code, this seems like the most
straight-forward and robust way to do it...
Prefixing a statement about some source code with 'without having looked
at the source-code' pretty much disqualifies it completely.
Tell you what: the source code to the x86 version of HotSpot is here:
http://hg.openjdk.java.net/jdk7/hotspot/hotspot/file/tip/src/cpu/x86/vm/
In particular, here's the table of assembly instructions used for each
bytecode in the interpreter:
http://hg.openjdk.java.net/jdk7/hotspot/hotspot/file/tip/src/cpu/x86/vm/templateTable_x86_32.cpp
Have a look at that, and let me know how hard you think it would be to
modify that to do overflow checking (and remember that you can't do it
everywhere, because existing code is written to use overflow - you have to
have some way of only doing it in specified bits of code).
tom
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