This directory builds libsgxlkl-user.so: the user-space image that hosts the C runtime (crt), which contains the dynamic program loader (ldso) and the the C library (libc).

SGX-LKL builds two ELF images that are loaded into the enclave.

- libsgxlkl.so (the kernel-space image)
- libsgxlkl-user.so (the user-space image)

Both are passed to the Open Enclave create_enclave() function in the path argument, which has the form:

"<enclave-elf>:<extra-elf>"

For example:

"libsgxlkl.so:libsgxlkl-user.so"

Open Enclave loads the two images into distinct ELF memory regions. This effectively isolates the symbols of the two images. The kernel enters the user-space image through its entry point given by its ELF header, passing state information and callbacks (through a C structure). The user-space image calls back into the kernel via these callbacks.

The main functions of the user-space image are to

- Initialize the C library
- Load the application program and any shared libraries
- Start executing the application program

During its execution, the program calls C library functions that may initiate syscalls. These syscalls are forwarded to the kernel-space image for handling.

This directory provides the following sources:

- userargs.h - defines the struct passed by the kernel to the entry point.
- enter.c - contains the entry point (**sgxlkl_user_enter()**).
- stubs.c - contains stubs that invoke callback functions.