"Boost context" for task switching on embedded Linux on ARM

On 18-08-09 17:55 , George Neuner wrote:
> On Wed, 8 Aug 2018 08:21:08 +0300, Niklas Holsti
> <niklas.holsti@tidorum.invalid> wrote:
>
>> The undefinedness of a cross-thread longjmp can be far more serious
>> than, say, shifting or overflowing a signed integer. A longjmp is
>> intended to *abandon* the current execution point and return to a point
>> *lower* (earlier) in the call stack. Some C or C++ systems might
>> implement this by unwinding the stack, frame by frame, until the setjmp
>> frame is reached. This will have drastic "undefinedness" if the setjmp
>> refers to another stack...
>
> But none do ... every implementation I have seen leaves the stack data
> intact and simply resets the CPU register(s).

Ok, but that is not proof that "none do".

> longjmp is NOT equivalent to throwing an exception, and, in fact, it
> is dangerous to use it that way in C++.  Using longjmp will NOT cause
> destructors to be called for local objects on the "abandoned" stack.

You cannot know if it will, or won't; it's explicitly undefined in the 
C++ standard.

>> It is not advisable, today, to try to misuse setjmp/longjmp for thread
>> switching.
>
> I already said that I don't advocate doing it, and that I merely was
> explaining it to the OP.

We agree.

> Maybe you prefer to conceal information about things you don't like,
> but I prefer to educate people and let them make up their own minds.

Becoming irritated, are we?

I'll stop here.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .