What is __kernel_vsyscall?

Question

I got a core that looks very different from the ones I usually get - most of the threads are in __kernel_vsyscall() :

  9 process 11334  0xffffe410 in __kern         


        

Answer 1

In addition to the already given good link to explanation of what linux-gate.so is, I'd like to answer "why is this core different?". Most recent (newer than 2.5.68) 32-bit Linux systems use VDSO page (aka linux-gate.so.1), and 64-bit systems will soon start as well (64-bit VDSO was introduced in kernel 2.6.24).

If you develop on an older system, or with an old glibc, then you would never see __kernel_vsyscall(), either because the kernel didn't create VDSO at all, or because (old) glibc doesn't use it even when VDSO is present.