Messages in this thread | | | Date | Fri, 22 Nov 2013 19:37:13 +0000 | From | Dave Martin <> | Subject | Re: [PATCH] ARM: unwinder: Handle Stackoverflow in unwind_exec_insn |
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On Sat, Nov 09, 2013 at 12:28:57PM +0530, Anurag Aggarwal wrote: > Thanks for your input Dave, > > I think there is another way to avoid the stack overflow and reduce > the number of checks also, > > Stack overflow will cause a problem only when we are backtracking the > last set of registers. > i.e when the difference between current SP and top of stack is less > than or equal to number of registers
Apologies, it looks like I failed to respond to this earlier...
Although that will usually be correct, there is no rule in the ABI to guarantee it.
> we can create two unwind_exec_insn, one without checks and one with checks. > > then we call the correct function from unwind_frame depending on the > difference of SP and top of stack. > > This will reduce the amount of checks every time we read a set of > registers from stack
That sounds like it might duplicate a lot of code, to optimise based on assumptions that may not always be true, for what really should not be a hot path in the kernel.
If you can find a tidy way of doing it, it would be certainly worth reviewing, but I still think it would be simpler just to do a simple bounds check for every word read from the stack -- it should be impossible for that to go wrong, even if some of the bounds checks are not stictly required.
Cheers ---Dave
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