Re: [git pull] core, x86: make LIST_POISON less deadly

[Avi Kivity]

Ingo Molnar wrote:
> * Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
>   
> > On Mon, 14 Jul 2008, Ingo Molnar wrote:
> >     
> > >  
> > > +config ILLEGAL_POINTER_VALUE
> > > +       hex
> > > +       default 0 if X86_32
> > > +       default 0xffffc10000000000 if X86_64
> > >       
> > This looks like a singularly bad pointer value on x86-64.
> >
> > Why not pick something that is *guaranteed* to fault? The above looks 
> > like any future setup that supports 41 bits of addressing and has 
> > extended the page tables (yes, it will happen eventually) will find 
> > that to be a perfectly valid address?
> >
> > It's also visually confusing, since it's visually very close to a real 
> > kernel pointer too.
> >
> > Grr.
> >
> > Why not use something sane like 0xdead000000000000, which has the high 
> > bit set but very fundamentally isn't a valid pointer, and never will 
> > be? And which is a *lot* more visually obvious too!
> >     
>
> initially i suggested that too - but such addresses raise a #GP instead 
> of a page fault so their decoding is a bit harder.
>
> We dont do any instruction decoding in #GP handlers to figure out what 
> happened, while in the pagefault case we know which address faulted, 
> etc.
>
> Perhaps we could try to make #GP handlers a bit more informative - 
> although decoding instructions will make things a bit more fragile 
> inevitably.
>
> Perhaps make it 0xffffcdead0000000 ?
>   

We could have the oops handler detect this address range, and point out 
the problem in plain English.

--
error compiling committee.c: too many arguments to function

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