Skip to content

Adding SafePOSIX Implementation of Syscalls

Jump to bottom
Çağlar Doğan edited this page Nov 29, 2020 · 22 revisions

Development Paths:

There are two main paths that can be taken in implementing a new system call. In both these paths, a system call is defined in Lind_GlibC.

First, a file in Lind_GlibC/sysdeps/nacl/ named X.c should be created for a system call X. In this file, a function to implement the system call should be defined with the name __X. This definition should be followed by weak_alias (__X, X) to denote the reference. (Aditional references can also be added here)

This file's full path (sysdeps/nacl/X.c) should then be added to the override_list in make_sysd_rules.py to make sure that this function is used.

This __X function should reference a function that can call the NACL_SYSCALL function. Such functions can be implemented in either sysdeps/nacl/lind_syscalls.c or sysdeps/nacl/irt_syscalls.c (after being defined in the respective header files).

1) Using native_client as a relay:

2) Implementing parts of the system call in native_client:

GlibC

To deliver the syscall to NaCl, add the interface of the syscall here:

  • Lind-GlibC/sysdeps/nacl/lind_syscalls.h
  • Lind-GlibC/sysdeps/nacl/lind_syscalls.c

Native Client

To pack the syscall and send it to Repy, add Remote Procedure Call (RPC) here:

  • native_client/src/shared/platform/lind_platform.h
  • native_client/src/shared/platform/lind_platform.c

To have SafePOSIX do the actual work, edit the syscall's NaCl implementation here:

  • native_client/src/trusted/service_runtime/nacl_syscall_common.c

Repy + SafePOSIX

This file is where RPC is accepted and syscalls are delivered to the dispatcher. Have the new syscall included here:

  • nacl_repy/seattlelib/lind_server.mix

To match the syscall with its Lind implementation, add a new pairing here:

  • nacl_repy/seattlelib/dispatcher.repy

Add the syscall's Lind implementation here:

  • nacl_repy/seattlelib/lind_fs_calls.py OR
  • nacl_repy/seattlelib/lind_net_calls.py

In this directory, you will also need to create a new .repy file that will act as the syscall's handler. There you do any mandatory checking and, after the syscall is implemented, pack the result back to NaCl.

Clone this wiki locally
⚡