Re: 4k stacks

[Denis Vlasenko <vda@ilport.com.ua>]

On Thursday 22 December 2005 23:53, linux-os (Dick Johnson) wrote:
> 
> Yesterday I sent a patch to add stack-poison so the stack usage
> could be observed.
> 
> Today I wrote a small program and tested the stack usage. Both
> the program and the patch is attached. The result is:
> 
> Offset : 2ec8f000	Available Stack bytes = 3104
> Offset : 2ecb1000	Available Stack bytes = 3104
> Offset : 2ee5f000	Available Stack bytes = 20
> Offset : 2f36d000	Available Stack bytes = 3104
> Offset : 2fd09000	Available Stack bytes = 3012
> Offset : 2fd0b000	Available Stack bytes = 3312
> Offset : 2fd0f000	Available Stack bytes = 2132
> Offset : 2fd2f000	Available Stack bytes = 2744
> Offset : 2fd57000	Available Stack bytes = 2900
> Offset : 2fdd5000	Available Stack bytes = 1400
> Offset : 2fe35000	Available Stack bytes = 2832
> Offset : 2ff3f000	Available Stack bytes = 776
> Offset : 2ff45000	Available Stack bytes = 3188
> 
> This, after compiling the kernel. I did not have 4k stacks
> enabled for this test so any crashing of the stack beyond
> one page will not hurt the system. This was on linux-2.6.13.4.
> 
> Anyway, I tried to enable 4k stacks and the machine would
> not boot past trying to install the first module. It just
> stopped with the interrupts disabled. So, I am now rebuilding
> the kernel back as I write this. That's why I am using 2.6.13
> at the moment.
> 
> Anyway, getting down to 20 bytes of stack-space available
> seems to be pretty scary.

+       movl    %esp, %edi
+       movl    %edi, %ecx
+       andl    $~0x1000, %edi
+       subl    %edi, %ecx

ecx will be equal to ?

+       movb    $'Q', %al
+       rep     stosb
--
vda