[jchw]

It's pretty much what OpenBSD is doing at bootup.

Truthfully though you're right, using typical linkers, this would be pretty slow; at least a few seconds for large binaries, to minutes for things as large as web browsers. However, for many binaries, linking can be done much faster; mold claims to be only 50% the runtime of using `cp` on the object files, which is fast enough to even re-link Firefox on-the-fly without it being unusable.

You could imagine writing a linker specifically for this case, that encodes information about the object files directly into the resulting bundle.

[blibble]

I thought openbsd did it after boot?

[dfox]

OpenBSD relinks sshd. Which is relatively small thing that is linked from relatively large objects (ie. it is the typical modern C code). Relinking thing like glibc on demand is going to be problematic, because it is structured as to allow small binary sizes for static linking and thus almost every function that is part of glibc API is a separate compilation unit and object file. Linking that into .so is slow, no mater what kind of optimalization tricks you implement in the linker.

[blibble]

doesn't matter how long it takes if you don't block the boot process doing it

you can link in the background at idle priority, and if you don't complete before reboot: no big deal

[saagarjha]

Relinking glibc would block the boot process.

[blibble]

how?

it's a dynamic library, and this isn't windoze with awful mandatory locking

as long as the underlying version is unchanged: there should be no problem whatsoever

[saagarjha]

glibc is going to get used by everything in userspace, so you’ll need it when you boot.

[jchw]

Yeah. That said, I'm suggesting that if it was really too slow, though, it'd probably be infeasible to relink libc, the kernel, etc. at bootup. It's not a direct comparison to be sure.