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by drewg123 2239 days ago
FreeBSD has a similar syscall translation layer (and has had it for over 20 years). They do it with a team of part-time volunteers. This is enough to maintain basic support, but FreeBSD still lack support for newer Linux syscalls which prevent things like the Linux binary version of Chrome from running on FreeBSD.
1 comments
tyingq 2239 days ago
Yes, but translating syscalls across two Unix like systems is likely much easier. Big parts of it even just straight mapping one number to another.
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drewg123 2238 days ago
This is somewhat true, but not entirely. You have to remember that FreeBSD and Linux share no common ancestors, and FreeBSD defines its ABI at the libc level, whereas Linux defines it at the syscall level. There are also subtle differences in how various internal kernel mechanisms work (such as flag definitions for calls). See linux_common_open() for an example of an "easy" straight mapping. https://github.com/freebsd/freebsd/blob/68a4c41e983228d54619...

This is true even between OSes that share a common ancestor. I was the maintainer of FreeBSD/alpha, and did the compat layer for OSF/1 / DEC UNIX / Tru64 starting with NetBSD's version and adding new calls, etc. The very easiest calls were the simple ones that both inherited from 4.3BSD or earlier (read, write). Medium were things that had diverged in different ways (stat, mmap), and for me the harder things were ABI handlers for the OSF/1 executable format (ecoff).

The hardest stuff was things at almost worked, except for maybe one flag was different, and it was hard to notice because an OSF/1 program would run for 5 minutes, and then coredump.

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yjftsjthsd-h 2238 days ago
> FreeBSD defines its ABI at the libc level, whereas Linux defines it at the syscall level

Actually, this really does make it more impressive than I'd realized, especially since FreeBSD didn't just shim libc in - I've run an Alpine Linux (musl-based) chroot on FreeBSD and that worked, which it wouldn't have if they just made a glibc-like wrapper. (I think.)

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tyingq 2238 days ago
That's a great rundown. I didn't mean to oversimplify the effort. Just to say that mapping Linux to Windows is likely much harder.

The lseek() call in your link is closer to what I meant by simple.

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