Re: Valgrind meets UML

[John Reiser <jreiser@BitWagon.com>]

Jeff Dike wrote:
> I would also appreciate suggestions on what sort of memory access state table
> to implement, and where best to put the declarations.  What I'm not clear
> on is what sort of access a buffer should have when it's in the care of
> the allocator (i.e. it's free).  If the allocator sticks information 
> temporarily in the buffer, then that needs to be stated.

Probably there will be some benefits, at least for a while, if valgrind for UML
"knows" the kernel allocators like valgrind for applications "knows" malloc+free.
Implementors of allocators can have bugs in the valgrind declarations they add.
An "independent" check based on documented externally-visible behavior can help.

Nested allocators (inner allocator grabs a large region, outer allocator performs
sub-allocations of small pieces from the large region) can be troublesome.

Implementing a four-state status {-, W, RW, RO} might be much more work,
because some accounting schemes are oriented naturally towards only three states
{-, W, RW}.  Also, there are contenders for two additional states: watchpoints
for READ and WRITE, such as "any read of a back-pointer of this doubly-linked
list", etc.

-- 
John Reiser, jreiser@BitWagon.com