Messages in this thread | | | Date | Thu, 12 Feb 2009 00:05:16 +0900 | From | Tejun Heo <> | Subject | Re: [PATCH 2/3] x86: Pass in pt_regs pointer for syscalls that need it |
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Brian Gerst wrote: > On Wed, Feb 11, 2009 at 9:48 AM, Tejun Heo <htejun@gmail.com> wrote: >> Tejun Heo wrote: >>>> I checked the disassembly of these functions and didn't see this >>>> happen on gcc 4.3.0. >>> Well, tracking down why run_init_process() is returning 0 with >>> -fstack-protector wasn't much of fun. These breakages are very subtle >>> and if we're gonna pass in pointer to pt_regs anyway and thus can >>> guarantee such breakage can't happen at no additional cost, I think we >>> should do that even if it means slightly more argument fetching in a >>> few places. >> In addition, if we do that, we can remove the horrible >> asmlinkage_protect() thing altogether. > > Like I said before, the tail-call optimization problem isn't limited > to just this set of syscalls. There are only two real ways to fix it. > 1) Set up a real stack frame for the syscalls instead of overalying > pt_regs, or 2) patch gcc to tell it not to touch the args area of the > stack.
Right, I forgot about the generic ones. We can pass pointer to pt_regs to all of them like x86_64 does but yeah we're likely to lose more than we gain by doing that. :-(
-- tejun
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