Re: kernel stack problem

[Fabiano Ramos <fabiano.ramos@gmail.com>]

> Hi List,
> 
> Recently I got into the problem that I think relates to the small size
> of kernel stack. I had a function of the following form:
> 
> void func()
> {
>      ...
>      //Block1
>     {
>          struct huge_var x;
>          ....
>          ....
>      }
>      ....
>      //Block2
>     {
>          struct huge_var y;
>          ....
>          ....
>      }
>      ....
> }
> 
> The above code resulted in stack overflow. I had an understanding that
> since the scope of variables x & y are limited to their blocks only,
> the space for them will be allocated and released when the block is
> entered and exited respectively. And hence the kernel stack will not
> overflow since both x and y will not occupy memory simultaneously (one
> instance of the variable can easily fit in the kernel stack).
> 

This is wrong. Although the scope is at _block_ level, all variables are
allocated on the stack at _function_ level. So, when entering func() all
variables within it, including x and y, are allocated.

> I solved this problem by having a single instance of struct huge_var
> declared immediately at function begining and reusing it in both
> blocks. But my question is when (and where) are the block scope
> variable allocated? In my previous case, were the two variables
> occupying two sperate memory areas simultaneously?
> 
> Ah, I understand that I should use kernel stack sparingly ... and will do so.
> Thanks,
> 
> Rajat
> 
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