libseccomp and 32 bit binaries on 64 bit hosts = bad

gistfile1.txt

# cat umount.c
#include <stdio.h>
#include <sys/mount.h>

int main(int argc, char **argv) {
    if (argc != 2) {
        fprintf(stderr, "Dumb\n");
        return 1;
    }

    if (umount2(argv[1], MNT_FORCE) != 0) {
        perror("umount");
        return 2;
    }

    return 0;
}
# grep Seccomp /proc/self/status
Seccomp:        2
# ls
native.umount  umount.c  x64.umount
# ./x64.umount /proc/cpuinfo
umount: Permission denied
# ./native.umount /proc/cpuinfo
#
# init 0
# #

x64.umount was compiled on the host (gcc --static), native.umount in the container