2002-10-15 05:54:15

by Dave Hansen

Subject: [RFC][PATCH] x86 transition to 4k stacks (0/3)

The kernel currently uses an 8k stack, per task. Here is the
infrastructure needed to allow us to halve that at some point in the
future.

This is a port of work Ben LaHaise did around 2.5.20 time. I split it
up and updated it for the new preempt_count semantics.

I split the original patch up into 3 pieces (apply in this order):
* clean thread info infrastructure (1/3)
- take out all instances of things like (8191&addr) to get
current stack address.
* stack checking (3/3)
- use gcc's profiling features to check for stack overflows upon
entry to functions.
- Warn if the task goes over 4k.
- Panic if the stack gets within 512 bytes of overflowing.
* interrupt stacks (3/3)
- allocate per-cpu interrupt stacks. upon entry to
common_interrupt, switch to the current cpu's stack.
- inherit the interrupted task's preempt count

Any suggestions on how to deal with "gcc -p" and old, buggy versions
of gcc would be appreciated.
--
Dave Hansen
[email protected]

2002-10-15 15:17:24

by Daniel Jacobowitz

Subject: Re: [RFC][PATCH] x86 transition to 4k stacks (0/3)

On Mon, Oct 14, 2002 at 10:59:55PM -0700, Dave Hansen wrote:
> The kernel currently uses an 8k stack, per task. Here is the
> infrastructure needed to allow us to halve that at some point in the
> future.
>
> This is a port of work Ben LaHaise did around 2.5.20 time. I split it
> up and updated it for the new preempt_count semantics.
>
> I split the original patch up into 3 pieces (apply in this order):
> * clean thread info infrastructure (1/3)
> - take out all instances of things like (8191&addr) to get
> current stack address.
> * stack checking (3/3)
> - use gcc's profiling features to check for stack overflows upon
> entry to functions.
> - Warn if the task goes over 4k.
> - Panic if the stack gets within 512 bytes of overflowing.
> * interrupt stacks (3/3)
> - allocate per-cpu interrupt stacks. upon entry to
> common_interrupt, switch to the current cpu's stack.
> - inherit the interrupted task's preempt count
>
> Any suggestions on how to deal with "gcc -p" and old, buggy versions
> of gcc would be appreciated.

You might have better luck with -finstrument-functions; I don't know if
it is supported as far back but I don't believe it was buggy. It has a
few fewer quirks than mcount profiling.

--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer