https://fzakaria.com/2026/06/21/nix-needs-relocatable-binari...
> The loader in Linux however natively supports the variable $ORIGIN which translates to “the directory containing the executable.”
https://man7.org/linux/man-pages/man8/ld.so.8.html
But, if ld.so supports $ORIGIN already, why does the kernel needs to support it also? Or rather, why can't the kernel leverage ld.so and do this entirely on userspace?
Besides, it allows for upgrades/downgrades to be done in a way that's much less error-prone.
Is the windows situation really all that different/better (with GetProcAddress in kernel32.dll)?
On Windows, things are less modular, so it's less of an issue. That said, there's also weird shenanigans when it comes to the CRT (which can be statically linked) vs ntdll (which provides the actual linker implementation), that can make certain niche features of the linker misbehave (delay loading in particular is weird).
You could make the argument that the glibc developers should split ld.so into its own subprojects. What for? That would just bring the extra responsibility of making sure that variations in glibc version work with variations in ld.so version for whatever reason.
What would happen in practice is that they would keep their version numbers in lock step, and systems integrators would use the same version. While the upstream glibc has to go through a dance of pretending that someone cares about their independence.
it seems nixos could set up a wrapper that invokes the right ld.so based on the executable. though at this point they could probably edit the ELF binaries and patch the fixed path to ld.so when nix is installing the program.
yeah, it seems strange that this needs kernel support. but more eBFP extension points are usually welcome, so sure, why not?
That's exactly what they're doing right now - though instead of being "when installing the program", it's "when compiling the program". The problem with hardcoding the path is that it pins the "nix store" (where nix installs all of its programs) to a hardcoded location. If you want to move it, you have to rebuild all your packages - which is suboptimal.
In theory, nix could have a system in place to just patch all binaries when moving the nix store, but that would be incompatible with content-addressed derivation and otherwise break some other nice properties of the nix store.
extern int errno;
You could have a very slim libdlopen that is used by both loader and libc, but I don't really see how that's any improvement/much different.
So your C stdlib does not have dlopen() (in fact, it's not really part of C stdlib in POSIX anyway!) but you can link with standard OS-level ABI to OS-provided runtime services like "find a library and symbol from it" - AmigaOS did something similar.
$ /lib64/ld-linux-x86-64.so.2
/lib64/ld-linux-x86-64.so.2: missing program name
Try '/lib64/ld-linux-x86-64.so.2 --help' for more information.
!1!
$ /lib64/ld-linux-x86-64.so.2 --version
ld.so (GNU libc) stable release version 2.34.
^^^^^^^^^^^^^^^^
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.There is much more value to be had in making glibc properly backward compatible so you can have a single one that can be used with everything than trying to make it so that you can swap everything around, creating extra complexity and compatibility risks.
You could only do that going forward though, and would be stuck, at least for a time, with the historic versions that still need extra handling. In an ideal world that wouldn't be needed, but in an ideal world you'd not need multiple versions of glibc at all so we aren't there.
Support in the kernel means that it will work even if applied to old packages that for some other reason need a held-back version of glibc. As mentioned elsewhere it also gives the feature to #! directives in scripts too.
- It would still not allow downgrades to work properly
- It would cause glibc/ld.so to have a harder time adding new features, as they now need to worry about incompatible versions being used together
Meanwhile, having different ld.so has many good use-cases, like simplifying development of ld.so itself, allowing them to swapped during updates in ways that are safer, etc...
And the eBPF binfmt support is a rather simple, generic mechanism that is likely to have many other use-cases beyond ld.so. So it's overall a pretty good resolution to the issue?
If you really need this, then there are options like swapping the linker with an older version or making a hardcoded linker that now points to an older one.
>It would cause glibc/ld.so to have a harder time adding new features, as they now need to worry about incompatible versions being used together
Every language runtime has to care about not breaking compatibility with apps that have been released already. This is not a new or unique problem.
Other libraries on the system is far more hit and miss, but glibc is quite compatible.
The other way around is harder though, you can't take a program built against a newer glibc and run it on an older version. So you generally need to spin up a container with some LTS distro and build your binary in it if you want it to be maximally compatible. (However, zig apparently is able to deal with this by shipping a mapping between glibc versions and symbol versions and doing the linking themselves. You can even use zig to link rust code using cargo-zigbuild and get that benefit.)
But if you want to be maximally portable: static linking against musl. Though beware that many things are slower in musl, such as the allocator.
Because Linux is completely independent from its user space. There is no "the loader in Linux", it just happens that GNU wrote one and it's widely used.
On most Linux systems this is regrettably `glibc` (in a container where you get to choose everyone chooses the superior option of `musl`), on all Darwin systems this is `libstandard`.
This thread is more concerned with Linux, so you are probably dealing with `/lib64/ld-linux-x86-64.so.2`, which operates in userspace but is by convention and opacity quite clearly part of "the system".
The kernel modification is a much bigger, much weirder side effect of a weird Nix loyalty test around shebang lines in shell scripts, on which is has opted to be intentionally and violently incompatible with everything for no benefit other than incompatibility.
It’s fair to argue about whether those things are really important or whether nix does this in the best way, but to claim that the only benefit is incompatibility is just obvious nonsense.
Disagreeing with you doesn't make something a rant. If it's not clear how deep my Nix expertise is I will demonstrate it to any level you like: I'm just as entitled to an opinion as you are and I would appreciate it if the nixpkgs community was a little less rude to anyone who disagrees with some dogma no matter their knowledge. The nixpkgs community is not regarded as healthy or friendly after an internecine faction war that split three ways twice, producing four implementations none of which work, and if that reputation is ever going to mend, it will be because less than every Nix person has precisely zero chill the nanosecond anyone disagrees with them about anything.
And you don't need to worry- it's perfectly obvious how deep your Nix expertise is.
The only thing I attacked are named instances of regrettable community malfunctions stripped of anything personal to an individual that hurt both current users of Nix and people who might experiment with systems they can reason about, saw an interaction like this, and did something less painful with their day. Because my evident and sincere concern for the future of Nix is framed as stark disagreement over a few particularly sacred cows.
At least on `comp.lang.lisp` you got your middle finger alongside a worthwhile education:
"There are some things in life that you do not do if you want to be a moral being and feel proud of what you have accomplished."
- Erik Naggum