Mail Archives: cygwin/2005/08/14/22:58:27
>Your demonstration code didn't use any Windows system calls. You were
>calling cygwin functions.
And printf doesn't use a Windows system call to write its output??
I fully admit to being in the dark about whether it is Windows or cygwin
that is being annoying here.
>I notice that you save your stack pointer in
>an automatic variable (saved on the stack), reset the stack pointer, and
>then get it back again. You are relying on the fact that the frame
>pointer doesn't change in that scenario.
A valid observation. I may need to push the fp onto the new stack and pop it
off before restoring.
>It is really not nonsensible for an OS to assume that it has control of
>the stack.
Lots of claims flying around, but no justification. An OS specified stack
can provide automatic extension to applications that are interested in that
feature, but apart from that I don't see why it should give a rip what an
app does with its stack.
>I already did earlier. Let's not loop.
You said that Windows has the TIB area. Ok, but if I restore the system
stack before talking to windows, I don't see any problem.
>And what happens when the compiler decides to allocate more memory on
>the stack than what seems possible from code inspection, like when
>there's a signal?
Well you've heard of sigaltstack() right? That's an API where you call
malloc()
to create some stack space. But I guess that API is "bad" because
it means that the OS is no longer "controlling" where the stack is right?
>And, I assume that there will be no recursion in your program? Because if
there
>is you're guaranteed heap corruption.
No, each function call has its own scheme environment and therefore its own
stack. So on a recursive call a new environment is allocated and thus a new
stack is allocated. Of course, most scheme recursion is tail calls and that
will be implemented with longjmp, thus re-using the same stack. By
allocating my own stacks I can longjmp down the stack (conceptually), which
is normally a no-no, but I've shown to work fine if you allocate your own
chain of stacks that are not garbage collected till they have no references.
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