On Thu, Mar 03, 2016 at 09:21:48PM -0500, Rich Felker wrote: > On Fri, Mar 04, 2016 at 02:39:38AM +0300, Dmitry V. Levin wrote: > > On Wed, Mar 02, 2016 at 09:29:24PM -0500, Rich Felker wrote: > > > On Thu, Mar 03, 2016 at 05:16:18AM +0300, Dmitry V. Levin wrote: > > > > On Wed, Mar 02, 2016 at 08:28:30PM -0500, Rich Felker wrote: > > [...] > > > > > What should be done about daemonized tracer mode? > > > > > > > > If we could switch stack before clone and then switch stack back in the > > > > child process, it would be a relatively simple change. > > > > Otherwise I don't see any simple options. > > > > > > I think it's possible to switch stack in the parent via sigaltstack > > > and raise, after which the cloned child can longjmp back to the stack > > > that was the parent's. > > > > This might work. Whatever signal is chosen, its handler and mask would > > have to be restored before the final execve call. > > The handler and mask could be restored before even calling clone; > actually, the whole machinery could be implemented as a wrapper for > clone that lets you pick whether the child runs a new function on a > new stack with the parent returning (like normal clone) or the parent > runs a new function on a new stack (with the child returning).
Sounds good. > > > Alternatively the child could just re-enter > > > main() on a new stack with a global var set to indicate that it's the > > > tracer child. > > > > I think it would be too risky to let the main bulk of strace code run > > on the new stack. > > Just in terms of stack size available? Or something else? Just the stack size. -- ldv
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