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

On 09/20/2014 02:20 AM, TONGARI J wrote:

2014-09-19 22:03 GMT+08:00 Larry Evans :

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On 09/18/2014 10:02 PM, TONGARI J wrote:

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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; }

Yep. Something like that. I, again, vaguely remember seeing code something like that in the Boehm GC source code. -regards, Larry