Re: [Valgrind-developers] Fedora Core 2

[Jeremy F. <je...@go...>]

On Tue, 2004-06-01 at 09:46 +0100, Tom Hughes wrote:
> In message <108...@lo...>
>         Jeremy Fitzhardinge <je...@go...> wrote:
> 
> > The initial problem is caused by VDSOs, which are placed low in the
> > address space.  When Valgrind clears out the client area in stage2, it
> > also clears out the sysinfo page, which happens to be where the munmap
> > syscall returns to...
> 
> I believe they are actually placed at a random address, or so the
> kernel source claims.

It's random within the range 0x00111000-0x01000000, I think.

> The code to setup the signal frame in arch/i386/kernel/signal.c is
> doing this:
> 
>   restorer = current->mm->context.vdso + (long)&__kernel_sigreturn;
> 
> Now if vdso is set to zero then current->mm->context.vdso will be null
> as no vdso will have been allocated. Hence restorer will be in zero
> page which seems rather nasty. I'm a bit surprised anything at all
> works with vdso's turned off in fact.

Yes that's pretty much exactly what I was expecting to see.  I guess
people don't run with vdsos off.

I'm trying to get a little standalone program to fail in the same way,
but it seems to work for reasons I don't understand yet.

	J