Messages in this thread | | | Date | Wed, 11 Feb 2009 10:10:20 -0500 | Subject | Re: [PATCH 2/3] x86: Pass in pt_regs pointer for syscalls that need it | From | Brian Gerst <> |
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On Wed, Feb 11, 2009 at 10:05 AM, Tejun Heo <htejun@gmail.com> wrote: > 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. :-(
x86-64 doesn't have the tail-call problem because it doesn't use the pt_regs on stack trick for syscall args. All the args are passed in registers.
-- Brian Gerst
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