On 07/01/2014 16:14, Herbert Valerio Riedel wrote:
Hello Simon,
On 2014-01-07 at 17:04:52 +0100, Simon Marlow wrote:
[...]
Yes, this is technically wrong but luckily works.
...but only as long as the code-generator doesn't try to push something on the stack, like e.g. when performing native 'call's which need to push the return-location on the stack...?
Right - in principle the code generator is in control of the stack so it can move the stack pointer whenever it likes, but in practice we know it only does this in certain places, like when making native calls, so these naughty functions just avoid doing that.
I'd very much like to have a better solution, preferably one that doesn't add any extra overhead.
I see... I've noticed there's a 'push() { ... }' construct that allows to push items on the stack; couldn't we have generalized version of that, taking a size-argument, declaring that specified amount of stack-space is user-allocated/controlled within the '{ ... }' scope?
We could push a stack frame, like we do for an update frame, but the problem is that we need a way to take the address of those stack locations. Taking the address of stack locations is also dodgy, because stacks move (say, during a native call). So it would still be unsafe. Also pushing a stack frame would incur an extra memory write for the info pointer, which is annoying. Cheers, Simon