Re: [Xen-devel] [PATCH v5 03/17] xenctx: Add -n (--display-stack-pages) option to output larger stack

[Don Slutz <dslutz@xxxxxxxxxxx>]

On 03/24/14 06:39, Ian Campbell wrote:
> On Sat, 2014-03-22 at 16:49 -0400, Don Slutz wrote:
> > As you can see from above, only the last 3 lines show up for "-n 3"
> OK.
>
> > > Why is the SP moving around in these pictures? I understood that this
> > > option was changing what was considered to be the limit of the stack,
> > > not the stack pointer itself, so shouldn't it be the base of the stack
> > > which is moving around?
> > These are pictures of the same stack at 3 different times.  And as you
> > can see
> > from above, this option does change the stack limit.
> There was no stack limit shown on your diagrams, only a stack pointer
> which was mysteriously changing. The SP is an actual register which is a
> property of the VM, changing it based on a xenctx surely doesn't make
> sense! (also it is not moving by page sized increments, which is odd
> even for the base, which ought to point at a page boundary surely).
>
> > > Perhaps if you had the diagram once and along side it had columns
> > > showing what is printed for each -n value as a range
> > >
> > > e.g.
> > >                                 None     -n 1
> > >          +------------------+              +
> > >          |                  |              |
> > >          |                  |              |
> > >          |                  |              |
> > >          |                  |              |
> > >          |                  |              |
> > >          +------------------+     +        |
> > >          |                  |     |        |
> > > SP --> |                  |     +        +
> > >          |                  |
> > >          |                  |
> > >          |                  |
> > >          +------------------+
> > >
> > > (or whatever the reality is)
> > >
> > > [...]
> > I will add this.  And some statement about each picture is for a
> > different time.
> Wait, what? Each picture is for a different time? How is that useful?
>
> The point of these diagrams is surely to illustrate the effect of what
> using this option would be at some fixed "snapshot" in time, adding a
> second axis of variation to the pictures is just confusing.
>
> Ian.
Ok, will adjust to just 1 picture.

   -Don Slutz

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