Re: [ANNOUNCE] kmemcheck v7

[Jeremy Fitzhardinge <jeremy@goop.org>]

John Reiser wrote:
> The valgrind+uml patches added a callback, "I am switching stacks >NOW<."
>   
Hm, I never particularly liked that approach because unless you do the 
whole thing in assembly it was never certain that there wasn't a 
basic-block break between them (ie, atomic with respect to valgrind).  
For the kernel that may be possible, but I was thinking of the general 
case where you might want to use setjmp or something.

> If possible then it is better to tell an interpreter what is happening,
> rather than requiring that the interpreter [try to] figure it out.
>   

Matter of taste really, but I tend to disagree.  If you say something 
like "addresses A-B, C-D, E-F are stacks", then the stack pointer 
changing from the range A-B to C-D is a pretty clear indication of stack 
switch, regardless of the mechanism you use to do it.  Of course, an 
explicit hint prevents an accidental push/pop of 32k onto an 8K stack 
from being considered a stack switch, but unless you actually know where 
the stacks are, you can't warn about it or prevent it from 
validating/invalidating a pile of innocent memory.

    J