Michael Schnell wrote: > > The vsyscall trick is a good one, and works with/without MMU, and > > with/without permission to disable interrupts in userspace. > > Unfortunately I don't find something about the "vsyscall trick" in the > Kernel sources not in the glibC sources.
Look in arch/arm/kernel/entry-armv.S for __kernel_cmpxchg, kuser_cmpxchg_fixup, and all the places where kuser_cmpxchg_fixup is called in that file. I haven't read the relevant glibc sources, but I have written code which uses __kernel_cmpxchg from my own application. > nor other hints on doing atomic operation > with the help of the vsyscall page (that is described as a memory area > that all processes can access, so it seems atomic operations are > required here, not provided). The vsyscall page is shared among all processes, but read only. (And sometimes per-CPU). Of course of you don't have an MMU or MPU then it can be written, but that's not meant to happen. kernel_cmpxchg accesses memory in your own process, that is, inside your own pthread_mutex_t structs, not in the vsyscall page. The point is that the code for kernel_cmpxchg is in the vsyscall page. That's part of the trick that makes it possible. -- Jamie _______________________________________________ uClinux-dev mailing list uClinux-dev@uclinux.org http://mailman.uclinux.org/mailman/listinfo/uclinux-dev This message was resent by uclinux-dev@uclinux.org To unsubscribe see: http://mailman.uclinux.org/mailman/options/uclinux-dev
