Re: [Boost-users] [context] How to set stack pointer in a platform-independent way?

Subject: Re: [Boost-users] [context] How to set stack pointer in a platform-independent way?
From: TONGARI J (tongari95_at_[hidden])
Date: 2014-09-20 03:20:03

2014-09-19 22:03 GMT+08:00 Larry Evans <cppljevans_at_[hidden]>:

> On 09/18/2014 10:02 PM, TONGARI J wrote:
> > Hi,
> >
> > The problem had been discussed here:
> > https://groups.google.com/forum/#!topic/boost-devel-archive/cl8B1oUPrVM
> >
> > But it's still not clear how to set the stack pointer portably, even
> after
> > examining the code of Boost.Coroutine. For now, Boost.Context only
> supports
> > downward stack, and Boost.Coroutine, which happened to be written by the
> > same author, just assumes that the stack always grows downward, which is
> > not really a portable implementation, if future Boost.Context supports
> > upward stack, Boost.Coroutine has to be changed as well.
>
> Several years ago, I had a look at the Boehm garbage collector:
>
> http://www.hboehm.info/gc/
>
> IIRC, it had to determine whether the stack grew upward or
> downward.  I can't remember where in the code that was,
> but I also vaguely remember reading (I think in the code
> commets) that the method was not completely portable.
>

I guess something like below should work?

    #include <iostream>

    __attribute__((noinline)) bool is_upward_test(char* a)
    {
        char b[32];
        return a < b;
    }

    bool is_upward()
    {
        char a[32];
        return is_upward_test(a);
    }

    int main(int argc, char** argv) {
        std::cout << is_upward();
    return 0;
    }