Support FreeBSD

[jasonwhite]

Currently, most architectures on Linux are supported, but other platforms such as FreeBSD are not yet supported.

The master list of FreeBSD syscalls is at https://cgit.freebsd.org/src/tree/sys/kern/syscalls.master. It should be possible to parse this and generate the necessary syscall tables. Unlike Linux, I believe this list is the same for all architectures under FreeBSD.

For the MacOS kernel, the list is similar: https://github.com/apple-oss-distributions/xnu/blob/main/bsd/kern/syscalls.master (But it looks harder to parse because of #ifdef usage.)

To support the addition of another platform besides Linux, I think the following structure should be used:

• syscalls::Sysno - Still has the syscall list for the current target architecture and target platform.
• syscalls::{target_arch}::Sysno will be the syscall list for the architecture target_arch and the current platform.
• syscalls::{target_os}::{target_arch}::Sysno will be the syscall list for target_os and target_arch.

This should be a backwards compatible change while still allowing the syscall table of other platforms to be available. That is, it might be useful to be able to access the FreeBSD syscall table even if the target OS is Linux.

Thus, the source tree should look like this:

• src/linux/{target_arch}.rs
• src/freebsd.rs - Might not need individual Sysno tables for each architecture.
• src/macos.rs

[AdamIsrael]

For MacOS, the syscalls have moved to https://github.com/apple-oss-distributions/xnu/blob/main/bsd/kern/syscalls.master

[jasonwhite]

@AdamIsrael Thanks! Updated.