Re: Why two stacks per process?

[Peter Teoh <tteikhua@xxxxxxxxxx>]

Robert P. J. Day wrote:

On Fri, 25 Apr 2008, Peter Teoh wrote:

  

In general, user cannot see kernel memory, but kernel can see user
memory.  To enforce this, all memory are not to be shared.  And this
is also enforce at the x86 hardware level - no OS feature is needed
(ie, windows/linux all worked in the same way)....the keyword to
search is called "stack switching".

And kernel have two stack - one for interrupt processing, and another
the normal non-interrupt processing.
    

i don't think that's entirely true.  on x86, anyway, there is a kernel
hacking feature for 4k stacks, which reduces the normal 8k stack size
to 4k, but compensates by creating another 4k stack just for
interrupts.  in the normal case, then, i'm assuming that interrupts
will simply "borrow" the kernel stack of the interrupted process, but
i'm willing to be corrected.

see the kernel hacking variable "CONFIG_4KSTACKS".

  

Erh.......I am not sure of this part.....as I only read the theoretical book - intel manual :-).   May be u are right.....I will dig into source code in my leisure time......thanks!!!

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