Actually it isn't that bad if you do it like dlsym()/dlopen() do it in
userspace. That is, have the system linker fill in dynamic syscalls,
possibly in a separate ELF section. This way you could version syscalls.
Furthermore, it may make sense to implement all syscalls through glibc,
so that the burden of maintaining obsolete/modified syscalls does not
fall onto the kernel. This already happens for most syscalls, but the
rest (mostly those Linux-specific) still rely on syscall numbers
defined as macros.
But that still will _not_ solve the problem, because:
- there are users which will only use older libc versions
- there are statically linked executables
- the modified/new syscall might not provide the same behavior, even
when used through a compatibility (glibc) wrapper
IOW, this problem can be reduced to any other instance where protocols
or APIs get changed. This usually isn't a problem, but the kernel can't
afford bloat to maintain compatibility.
I hope this makes the issue more clear.
Cheers,
Eduard
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