Query on vma and User mode Stack

Query on vma and User mode Stack

[Krishnakumar R]

Hi All,

I was trying to figure out the connections between vma's and user stack
segment.

I compiled  a C program in which I printed the address of a local variable
(under the assumption that it fall into the stack segment address).
The address which got printed was '0x9ffffc74'. (this is 386 based machine).

I printed out the start_stack from the mm_struct of the process.
I got the value: '0x9ffffec0'. There were 5 vmas for the process of which
the 5th vma started at 0x9ffff000 and ended at 0xa0000000.

Considering the vma address, I feel that stack segment falls into
this area. Also 0x9ffffec0 >0x9ffffc74, means that the stack grew down.
But then shouldn't the stack segment start from the end of the vma (near
0xa0000000 ?

I have heard that user stack growth happens dynamically. Is this the 
manifestation of such a case (when the the space fully is required
stack will start from the end of the vma) ?

Thanks and Regards,
KK.
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