I won't try to "point" to documentation.... Each co-routine should have it's own separate stack. Best practices with stack management today have a sufficiently large stack that grows and then terminates in unmapped memory. If it is attempted to grow the stack too much, then the program gets a memory exception (SIGSEGV on systems that use it). Think about a recursive routine with relatively large local data structures (stack-based). Such a routine could overwrite any amount of stack, finish, and then return with no errors. The current PicoLisp implementation sounds like, then, when a co-routine switch occurs, the switched to routine could find it's stack corrupted. And certainly operating system events could overwrite things deeper on the stack during a context switch.
Rand On Mon, May 20, 2013 at 6:43 PM, Alexander Burger <a...@software-lab.de>wrote: > Hi all, > > since nearly three years PicoLisp supports coroutines (64-bit version). > Now suddenly it occurred to me that the way I implemented them might be > illegal. > > The problem is how individual stacks for the coroutines are allocated. I > do this by reserving space on the stack (by decrementing the stack > pointer) upon starting a new coroutine. Execution of that coroutine may > be suspended (with 'yield', so that execution continues in the main > program or some other coroutine), to be resumed later. > > Switching between individual (co)routines is done by moving the stack > pointer up and down between the corresponding stack frames. Everything > seems to work fine - though I haven't used coroutines in serious > projects yet. > > > Now I remember to have read that (in POSIX?) no valid data should be > stored *below* the current position of the stack pointer. Is that really > the case? I can't find any conclusive information about that. > > This switching between stack frames, as described above, of course > leaves temporarily suspended stack frames *below* the stack pointer, > while it points into a higher frame. Does this mean that the operating > system might dispose or overwrite them? For example, when paging is > required? > > Interrupts are probably not a problem, as they push their contexts on > the system stack. > > Some sources say that even GCC stores (small amounts of) data below the > stack pointer, while others (possibly some ABIs from Intel) say this is > an absolute no-no. > > Can anybody point to a definite answer? > > ♪♫ Alex > -- > UNSUBSCRIBE: mailto:picolisp@software-lab.de?subject=Unsubscribe >
