On Fri, 2010-01-15 at 15:44 -0800, Jim Keniston wrote: > On Fri, 2010-01-15 at 12:12 +0100, Peter Zijlstra wrote: > .... > > > > Adding the probe uses the fact that (most) executable mappings are > > MAP_PRIVATE and CoWs a private copy of the page with the modified ins, > > right? > > > > What does it do for MAP_SHARED|MAP_EXECUTABLE sections -- simply fail to > > add the probe? > > If the vma containing the instruction to be probed has the VM_EXEC flag > set (and it's not in the XOL area) we go ahead and try to probe it. I'm > not familar with the implications of MAP_SHARED|MAP_EXECUTABLE -- how > you would get such a combo, or what access_process_vm() would do with > it.
I'm not sure how you'd get one, the user has to explicitly create one I think, regular loaders don't create such things, but maybe JITs do. The problem is that for MAP_SHARED you cannot CoW the page, you have to modify the original page, which might get written back into a file if its file based, not something you'd want to have happen I guess.
