How to check the vsyscall mode

Question

I am struggling to find out how to check how the [vsyscall] table is configured (to native or emulate). The setting should be set in a variable called vsyscall_mode. Can anyone shed any light on how to check this setting?

By re-running cat /proc/self/maps I have observed that the memory mapped area for [vsyscall] does not change, which the [vdso] does. Does this mean that the setting for vsyscall is set to native?

Answer 1

vsyscall mode is set in kernel configuration so you can be able to choose between native and emulation.

for fish-shell:

cat /usr/src/linux-headers-(uname -r)/.config | grep VSYSCALL 

for bash:

cat /usr/src/linux-headers-$(uname -r)/.config | grep VSYSCALL 

output on debian 8 (as example):

CONFIG_GENERIC_TIME_VSYSCALL=y
CONFIG_X86_VSYSCALL_EMULATION=y