Re: [boost] [context] Linux x64 / printf

Subject: Re: [boost] [context] Linux x64 / printf
From: Daniel Larimer (dlarimer_at_[hidden])
Date: 2012-09-11 20:33:55

On Sep 11, 2012, at 8:27 PM, Daniel Larimer <dlarimer_at_[hidden]> wrote:

> On Sep 11, 2012, at 12:56 PM, Oliver Kowalke <oliver.kowalke_at_[hidden]> wrote:
> 
>> Am 11.09.2012 18:14, schrieb Daniel Larimer:
>>> On Tue, Sep 11, 2012 at 1:57 AM, Pekka Seppänen <
>>> pekka.seppanen_at_[hidden]> wrote:
>>> 
>>>> On 11.9.2012 5:00, Daniel Larimer wrote:
>>>>> I modified the 'jump.cpp' example and added the line marked CRASH in f1()
>>>>> 
>>>>> #include <cstdlib>
>>>>> #include <cstring>
>>>>> #include <iostream>
>>>>> #include <vector>
>>>>> 
>>>> ...
>>>> 
>>>>> void f1( intptr_t)
>>>>> {
>>>>>      std::cout<<"hello "<<0;  // WORKS
>>>>>      printf( "hello %d", 0 ); // <<< CRASH
>>>>>      std::cout << "f1: entered" << std::endl;
>>>>>      std::cout << "f1: call jump_fcontext( & fc1, & fc2, 0)" <<
>>>> std::endl;
>>>>>      ctx::jump_fcontext( & fc1, & fc2, 0);
>>>>>      std::cout << "f1: return" << std::endl;
>>>>>      ctx::jump_fcontext( & fc1, & fcm, 0);
>>>>> }
>>>> I guess printf should be pulled from cstdio (not that you should use it,
>>>> printf that is, in the first place), so perhaps your compiler is using some
>>>> short of build-in instead which causes the crash.
>>>> 
>>>  I am just using the standard compiler... the reason I was using printf()
>>> is because I wanted to avoid including all of iostream in every build...
>>> accelerate compile times.
>>> 
>>>  Fortunately, I wrap all of my console prints in a debug macro that made
>>> it easy for me to switch to iostream at the expense of doubling my compile
>>> times.
>>> 
>>>  If it were simply a 'stack size' issue then it still wouldn't solve my
>>> problem because I really to do want the minimum stack size as I have a lot
>>> of async operations where the state is managed on the 'stack'.
>>> 
>>> 
>> your app does not crash (cstdio must be included) on my x86_64 Linux system
>> 
>   You are right, printf() does not crash, but fprintf( stderr, "hello %d", 0 ) does seem to crash... I simplified it too much for the bug report.  To be fair, fprintf( stdout, "hello %d", 0 ) also works... so it appears to only be stderr that is crashing.
> 
>   Using fprintf( stderr, "..." ) in main works just fine, it is only from the context of f1() that there is a problem.

      I can confirm that using default_stacksize() instead of minimum stack size fixes the problem.  So it would appear that stderr must use the stack for scratch space.  So apparently, linux has a min stack size of 8kb which is relatively small!  

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