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Subject4k stacks
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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.


Cheers,
Dick Johnson
Penguin : Linux version 2.6.13 on an i686 machine (5589.54 BogoMips).
Warning : 98.36% of all statistics are fiction.


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