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points

by okanat11 hours ago |

comments

by uecker10 hours ago|

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It depends on functions defined in a standardized ABI.

by okanat10 hours ago|

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You'd expect that but, no. That's why you cannot load glibc-linked binaries in a Musl distro. Edit: that's why the hacks like the original post is needed, as well.

The ABI is strongly dependent on explicit libc implementation in current Linux systems. There is no libc independent ABI on Linux.

by uecker10 hours ago|

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Sorry, can you be more specific. I do not understand what the problem is. If Musl does not implement support for the ABI, this would be a musl problem?

by okanat10 hours ago|

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There is no libc independent ABI. ABI doesn't purely mean just calling conventions.

When you compile libc, you also get a binary loader ld-linux.so with it. They are not two independent components of a system.

Basically all .so files compiled with glibc require the ld-linux.so that's also generated by that glibc (or a later version, if they didn't break the binary compatibility).

There are a lot of stuff that's executed by ld-linux.so and glibc that are not explicitly documented but they are absolutely necessary for your program to start and correctly initialize things like global variables or signal handling or loading other dynamic libraries. Some of that functionality sits in ld-linux.so and some of that in glibc. They have circular dependencies to each other. glibc expects ld-linux.so to put things in certain order but ld-linux.so also must load glibc first to have access to certain APIs. They are not part of System V ABI. They are not documented.

Musl maybe can implement this but it is simply reverse engineering what glibc did and then playing a game of cat and mouse. There is no independent ABI standard.

by uecker2 hours ago|

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Sorry, again this too vague for me. What is the exact problem with atomics and thread_local in C that would make the ABI dependent on a specific version of glibc? I know the ABI is not just calling convention and e.g. for atomics may involve calling a function from libatomic. But from my understanding, this is all part of a standardized ABI that does not change and can be provided by different implementations.

Then, what is the exact reason a library compiled against glibc must be loaded by a specific ld-linux? I could see that this is true for C++ perhaps, or when you use very special features, but I do not see this for C.

I often compiled programs against one version of glibc and run it against a different version, so I know there is not a tight coupling. So please be specific in explaining in what scenarios this would break.