Re: guarantees of exception safety in Lua

[David Kastrup <dak@...>]

David Given <dg@cowlark.com> writes:

> Diego Nehab wrote:
> [...]
>> I remember somebody from NASA at a Lua conference some time back saying
>> lots of people that write software there don't believe in dynamic memory
>> allocation. They don't even believe in functions from the C runtime. They
>> write their own stuff from scratch, just to make sure. Everything
>> static, no recursion. Just for loops. That gives me a warm feeling of
>> safety.
>
> That's actually very traditional in the hard embedded world --- if you
> look at platforms like VxWorks or Nucleus you're frequently see that
> dynamic memory allocation --- malloc --- is an optional feature.
> Instead, all data is stored in globals, which get allocated by the
> linker at compile time.
>
> Going even further, if you don't need reentrant functions, you can do
> away with the stack --- all function parameters become global, and each
> function gets exactly one return address. This can be useful on really
> resource-limited machines, because you can make much more efficient use
> of memory; stacks inherently waste memory because you have to allow
> space for them to expand into.

Fortran machine architectures tended to be stackless.  I remember the
CDC machines (Cyber 175 was what I used) having a "return jump
instruction".  Before jumping to the given destination, it wrote a jump
to _after_ the RJI instructions into the memory word preceding the
destination.  When the called function finished, it jumped to this
instruction preceding its body.

Of course, recursive function calls were not possible.

-- 
David Kastrup