Messages in this thread | | | Date | Tue, 19 Sep 2006 14:11:01 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH] Linux Kernel Markers |
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* Martin Bligh (mbligh@google.com) wrote: > Mathieu Desnoyers wrote: > >* Martin Bligh (mbligh@google.com) wrote: > > > >jump. I think it would be doable to overwrite a 5+ bytes instruction with > >a NOP > >non-atomically in all cases, but as the instructions not in the prologue > >seems to > >be smaller : > > > >prologue on x86 > > 0: 55 push %ebp > > 1: 89 e5 mov %esp,%ebp > >epilogue on x86 > > 3: 5d pop %ebp > > 4: c3 ret > > > >Then is can be a problem. Ideas are welcome. > > Ugh, yes that's somewhat problematic. It does seem rather unlikely that > there's a function call in the function prologue when we're busy > offloading stuff onto the stack, but still ... > A function call is not the cause of the problem : an interrupt/trap is.
> For the cases where we're prepared to overwrite the call instruction in > the caller, rather than insert an extra jump in the callee, can we not > do that atomically by overwriting the address we're jumping to (the > call is obviously there already)? Doesn't fix function pointers, etc, > but might work well for the simple case at least. > I don't think we have any guarantee that the function pointer in the call is aligned, so I guess it would not be an atomic replacement.
Mathieu
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