[Vm-dev] Amazing ARM simulator experience

[Dimitris Chloupis]

My first computer that my father bought me in 1988 was an Amstrad CPC 6128
, with a 4 Mhz CPU and 128kb Ram

My latest computer is a late 2013 quad core 3 Ghz iMac with 8 gb memory.
Which makes it at least 3000 times faster than my Amstrad , technology has
come a long way the past 30 years. I could not imagine this future even in
my wildest dreams.

By Gdb you mean the GNU debugger ?

On Wed, Jun 1, 2016 at 8:43 PM Eliot Miranda <eliot.miranda at gmail.com>
wrote:

>
> Hi All,
>
>     just had to tell people about this morning's experience using the ARM
> simulator.  I've been building Smalltalk VMs since 1983, so 33 years.  My
> first on the Three Rivers PERQ was dog slow.  My undergraduate project was
> done the the National Semiconductor 32016 based Whitechapel Computer Works
> workstation and its and 32032-based successor.
>
> This morning I was revamping register management in Cog's ARMv5/v6 back
> end, making more registers available by using two of the C argument
> registers for two of registers the Cogit assigns to various fixed tasks,
> and using store and load multiple instructions to save and restore
> concisely the registers around calls into the runtime.
>
> Remember the architecture here.  The simulator generates ARM machine code
> into the ByteArray that re[resents the address space, holding all of
> generated machine code, a small C stack, and the Smalltalk heap.  A plugin,
> derived from Gdb's ARM simulator written in C, interprets that machine
> code, running for a couple of milliseconds at a time in a loop, applying
> breakpoint calculations, and asserts on every call into the run-time, and
> that calls into the run-time and accesses of variables in the simulator is
> done by using illegal addresses in the generated machine code.  Each
> illegal access causes the Gdb-derived machine code interpreter to return
> with an error, this error is turned into an exception, the handler for
> which maps the specific illegal address into a variable or message
> selector, accesses the variable or activates the message selector,
> providing the result, and allowing the execution to continue.
>
> In changing the register management I had a test case that worked, an
> image that prompted for an expression ands evaluated it, which worked both
> in the simulator and with the generated VM.  But the real VM, crashed when
> used on a proper image.  So to debug I started launching the real
> interactive image in the simulator.
>
> Well, the amazing experience is that that image, whose machine code is
> being _interpreted by a C program_ feels /faster/ than my 32016 based
> implementation back in 1984-ish.  Quite amazing.  I can open windows, type
> text, access source code (was playing with Message Names) etc.  It's
> sluggish, but usable.  Amazing how fast modern machines are.  All on my
> 2012 vintage 2.2 Ghz Core i7 MacBook Pro.  I'm blown away :-)
>
> _,,,^..^,,,_
> best, Eliot
>
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