Re: [Valgrind-users] trampolines - how to work around

[Karl <kh...@tr...>]

On 2005-05-25 17:44:58 -0700, Jeremy Fitzhardinge wrote:

> How about "generate self-checking code if the code is being fetched
> from a writable page"? That will never happen in normal operation,
> since all code is mapped read-only. It could be fooled by someone
> changing page permissions with mprotect (write some code into a
> page, make it RO, execute it, make it RW, change it), but you could
> fix that by clearing the translation cache for a memory range when
> either switching it from RW->RO or RO->RW (one or the other should
> do the trick).

You can't fix it by clearing translations only on rw->ro transitions.
If you do, then after an ro->rw transition, you would have
non-self-invalidating code based on writeable memory.

The other option works: then, after a rw->ro transition, you would
have self-invalidating code based on read-only memory, which is
inefficient but correct.

-- 
Karl Hasselström, kh...@tr...
      www.treskal.com/kalle