In what sense do binary interpreter / loader, GCC compiler, C library and system C/C++ ABI dependent on each other? I have certainly mixed different versions of all these components without problems so far.

▲

okanat an hour ago | parent | next [-]

When you compile GCC you need to provide a full glibc installation as your target. It is also a dependency of libstdc++.

C++ global/static variable initialization depends on the specific version of glibc (they don't usually break compat, but they can and they did in the past) which also provides ld-linux.so that loads those global variable placeholders in the correct manner such that glibc and libstdc++ can initialize them correctly.

This is just one example. Thread local variables and behavior of things like pthreads with signal, fork etc all depend on glibc.

	▲	uecker an hour ago \| parent [-]
		I can't comment on the C++, I can imagine there plenty of issues, but for C I don't see this. You need some libc if you compile with gcc, but this generally does not introduce a hard version dependency on the specific version (there may be a minimum requirement if you compile against a new version that a symbol with a different ABI).

▲

pg83 an hour ago | parent | prev | next [-]

For example, the itanium unwind ABI implementation lies between these three entities.

▲

mananaysiempre an hour ago | parent | prev | next [-]

I don’t imagine that you’re unaware of any of this, but: ld.so and libc.so are heavily interdependent in deliberately undocumented ways with Glibc and outright the same file with shared Musl. And while you might usually get away with using any old GCC with the right architecture and ABI (especially for C; cf the musl-gcc hack), technically it needs to be built to target a specific libc version (particularly via symbol versioning; I’ve long wanted to gather a set of patches to build an old Glibc and subsequently a cross-compiler using a new GCC so I could avoid PyPA’s manylinux monster or its moral equivalent for compatible dynamic binaries in simple cases). The C compiler of course is tied to the C ABI, and this wouldn’t be really worth mentioning except for the time where the GCC devs accidentally the whole SysV i386 ABI and pretended that the stack was always 16-byte aligned, why do you ask, except on RHEL. The C++ parts I can’t really comment on.

	▲	uecker an hour ago \| parent [-]
		I am not really sure. For ld.so and libc.so I may believe this. The C ABI is very stable, and if you use a new symbol from a newer glibc, you certainly depend on it, but this can also be avoided. In any case, I do not see what is fundamentally misdesigned here. I can't quite image how it could work differently. If you upgrade something so that the e ABI changed you natually need to update other components. Static linking certainly seems a very poor replacement for this.

▲

duped an hour ago | parent | prev [-]

The interpreter/loader is glibc and a key part of bootstrapping an executable built against glibc is loading libc itself before continuing on to load the program. Versioning is a problem when distributing binaries linked against a newer glibc to distros that ship an older one. The C compiler doesn't really care as much.

▲

okanat an hour ago | parent [-]

> The C compiler doesn't really care as much.

Until you define a thread local variable (C11) or use atomics (also C11) or define a global with an initial value. Then it happily generates code that depends on "whatever my target glibc + ld-linux.so needs".

▲

uecker an hour ago | parent [-]

It depends on functions defined in a standardized ABI.

▲

okanat an hour ago | parent [-]

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.

▲

uecker 42 minutes ago | parent [-]

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?

	▲	okanat 33 minutes ago \| parent [-]
		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.