Messages in this thread | | | Date | Sat, 31 Jan 2009 11:45:59 -0600 | From | Martin Hicks <> | Subject | Re: [PATCH] x86: push old stack address on irqstack for unwinder |
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On Sat, Jan 31, 2009 at 01:39:21AM +0100, Ingo Molnar wrote: > > * H. Peter Anvin <hpa@zytor.com> wrote: > > > H. Peter Anvin wrote: > >> Martin Hicks wrote: > >>> Hi, > >>> > >>> KDB was using this information. Could this be pushed towards 2.6.29 > >>> please? > >>> > >>> This re-adds the old stack pointer to the top of the irqstack to help > >>> with unwinding. It was removed in commit > >>> d99015b1abbad743aa049b439c1e1dede6d0fa49 > >>> as part of the save_args out-of-line work. > >>> > >> > >> This bothers me... why should we add even a single instruction to what > >> is arguably the single hottest path in the kernel to support an > >> out-of-tree debugger, especially if kgdb (which is in-tree) doesn't > >> need it? > >> > >> What does kgdb do differently (or is kgdb broken too)? > >>
I was searching around, trying to find out if there was another way for kdb to do this, and I think removing the backlink is breaking other stuff also. dump_trace() in dumpstack_64.S is using the same trick as KDB to trace out of the interrupt stack:
/* * We link to the next stack (which would be * the process stack normally) the last * pointer (index -1 to end) in the IRQ stack: */ stack = (unsigned long *) (irqstack_end[-1]); irqstack_end = NULL; ops->stack(data, "EOI"); continue;
mh
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