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by toast0 771 days ago
> The system ABI of Linux really isn't the syscall interface, its the system libc.

Which one? The Linux Kernel doesn't provide a libc. What if you're a static executable?

Even on Operating Systems with a libc provided by the kernel, it's almost always allowed to upgrade the kernel without upgrading the userland (including libc); that works because the interface between userland and kernel is syscalls.

That certainly ties something that makes syscalls to a narrow range of kernel versions, but it's not as if dynamically linking libc means your program will be compatible forever either.
1 comments
jimmaswell 771 days ago
> That certainly ties something that makes syscalls to a narrow range of kernel versions

I don't think that's right, wouldn't it be the earliest kernel supporting that call and onwards? The Linux ABI intentionally never breaks userland.

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toast0 771 days ago
In the case where you're running an Operating System that provides a libc and is OK with removing older syscalls, there's a beginning and an end to support.

Looking at FreeBSD under /usr/include/sys/syscall.h, there's a good number of retired syscalls.

On Linux under /usr/include/x86_64-linux-gnu/asm/unistd_32.h I see a fair number of missing numbers --- not sure what those are about, but 222, 223, 251, 285, and 387-392 are missing. (on Debian 12.1 with linux-image-6.1.0-12-amd64 version 6.1.52-1, if it matters)

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