Default syscalls not implemented in Posix OS

[ytournier]

Using the Android binaries provided in the rootfs, Qiling stops because of tgkill and sigaltstack syscalls are not implemented.

The code snippet below must be added in the signal.py file which is defined for the Posix OS:

def ql_syscall_sigaltstack(ql: Qiling, ss: int, oss: int):
    return 0


def ql_syscall_tgkill(ql: Qiling, tgid: int, tid: int, sig: int):
    return 0