System calls translation

The pipeline uses kernel as a source of truth. Unfortunately, all other options proved to be either incomplete or imprecise.

System call names, numbers and entry points are extracted from kernel sources.

TODO: consider extracting names, numbers and entry points from vmlinux!

System call parameters are extracted from vmlinux DWARF.

Automatic translation happens between system calls with the same entry point if entry point parameters are compatible.

Checkout kernel

Assume the kernel checkout is at $KERNEL_SRC.

Extract system calls names, numbers and entry points

This is specific for architectures. The script does extraction for arm, arm64, x86, x86_64 and riscv64.

In addition, the script checks entry point prototypes and marks those without parameters. System calls without parameters do not need compatibility checking (and they don't have corresponding __do_sys_* functions, see "Extract system calls parameters").

Unfortunately, extracting full info about parameters from prototypes is a bad idea. Most architectures have specific calling conventions for system calls, so even the number of parameters may vary. But, hopefully, "no parameters" means the same thing everywhere.

./extract_syscalls_from_kernel_src.py $KERNEL_SRC/common > ./kernel_syscalls.json

Extract system calls parameters

Entry point sys_foo is a function that gets system call parameters in a form of struct ptregs*. SYSCALL_DEFINEx macro unpacks parameters and calls implementation function __do_sys_foo which receives parameters normally.

__do_sys_foo functions are usually inlined and do not exist in symbols table. However, DWARF should still have these functions.

To get parameters info in our common .json API form, do:

Build kernel for arch with debug info. Assume this is VMLINUX_RISCV64.

Extract the list of __do_sys_* functions for arch:

./gen_kernel_syscalls_symbols.py riscv64 ./kernel_syscalls.json > ./symbols_riscv64.txt

Use dwarf_reader to get .json API info for these functions:

dwarf_reader --filter=symbols_riscv64.txt VMLINUX_RISCV64 > ./kernel_api_riscv64.json

Generate system calls translation

Now there should be files like:

kernel_syscalls.json (common system calls info)
kernel_api_riscv64.json (src arch system calls API)
kernel_api_x86_64.json (dst arch system calls API)
custom_syscalls.json (translation exceptions)

Run the script to generate code for translation function:

gen_kernel_syscalls_translation.py riscv64 x86_64 \
> kernel_api/gen_syscall_emulation_riscv64_to_x86_64-inl.h