How to make a custom system call in Google Native Client

Question

I have made the necessary changes to the following files irt_syscalls, nacl_syscalls, nacl_syscalls, nacl_syscalls_common, nacl_syscalls_handler_gen.py

but I get Undefined reference to NaClSysLibcall (the system call I'm trying to make) while compiling NaCl code

Answer 1

since you are implementing a custom syscall, i'll assume you do not want to run inside of chrome and you just want to run code via sel_ldr.

IIRC the SDK, whether you want newlib or glibc, was built in the chromium tree, and getting the C syscall wrapper to build is probably going to be a pain since you'd need to fetch all of chromium; worse, the SDK source may have already been eradicated from the chromium tree.

an easier way might be to just write your own syscall wrapper that calls the address in the trampoline region that corresponds to the syscall. you can disassemble an existing syscall wrapper to see what the code ought to look like.