Re: Do we really need virtual machines?

Nicola.Musatti@ObjectWay.it (Nicola Musatti) writes:
>According to their proponents virtual machines such as JVM and CLR are
>the solution to all our (programming) problems, of which portability
>is but one.
>
>Maybe it's just because when I learnt programming the p-machine was
>considered an interesting oddity, but with the exception of code that
>really must run unchanged on unknown platforms, I fail to see what do
>I gain from a virtual machine that I don't already get from a good old
>compiler/runtime support/standard library chain.


One thing you get is a somewhat obfuscated form of the source code,
and not being able to read the source code directly seems to be
important in some areas.


Maybe that's why JVM and CLR seem to be much less popular among free
software developers than among proprietary software developers.


>After all, isn't gcc the most ported virtual machine of all?


GCC has been widely retargeted, but portability of C (or GNU C) code
requires quite a bit of work, because C allows (and requires)
accessing a lot of stuff in the environment outside the gcc run-time
library.


>Now, this being the compiler forum, I'm interested in learning about
>the advantages of virtual machines from the compiler writer
>perspective.


Well, for VMs and compilers in general, VMs are a kind of intermediate
representation with a number of advantages:


- they can be interpreted easily and efficiently.


- they can be saved and loaded relatively simply.


- they isolate the front end from the back end relatively well.


    - anton
--
M. Anton Ertl
anton@mips.complang.tuwien.ac.at
http://www.complang.tuwien.ac.at/anton/home.html

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