Comment by eklitzke
3 years ago
This is all correct and I'd also add that ld.so doesn't need to have any special knowledge of glibc (or the kernel) in the first place. From the POV of ld.so, glibc is just another regular ELF shared object that uses the same features as everything else. There's nothing hard-coded in ld.so that loads libc.so.6 differently from anything else. And the only thing ld.so needs to know about the kernel is how to make a handful of system calls to open files and mmap things, and those system calls that have existed in Linux/Unix for eternity.
Needs to have? In an ideal world, probably not. Has and uses? Definitely. For one thing, they need to agree about userland ABI particulars like the arrangement of thread-local storage and so on, which have not stayed still since the System V days; but most importantly, as a practical matter, ld.so lives in the same source tree as glibc, exports unversioned symbols marked GLIBC_PRIVATE to it[1], and the contract between the two has always been considered private and unstable.
[1] https://sourceware.org/git/?p=glibc.git;a=blob;f=elf/Version...