A strong symbol anywhere in an executable must override any
weak symbol used in any library. This means that the weak symbol
must be overridden by a strong symbol even if the strong symbol
is in a dependent library. This means we need to perform relocations
twice, and resolve weak symbols globally before attempting to resolve
them locally. Consequentially we need to defer performing any
initialisations until after we have performed the second round of
relocations.
Loader.so now just performs the initial self relocations and static
LibC initialisation before handing over to ELF::DynamicLinker::linker_main
to handle the rest of the process.
As a trade-off, ELF::DynamicLinker needs to be explicitly excluded from
Lagom unless we really want to try writing a cross platform dynamic loader
The dynamic loader exists as /usr/lib/Loader.so and is loaded by the
kernel when ET_DYN programs are executed.
The dynamic loader is responsible for loading the dependencies of the
main program, allocating TLS storage, preparing all loaded objects for
execution and finally jumping to the entry of the main program.
ELF::DynamicLoader now validates the ELF header and the program headers
in its constructor. The requested program interpreter from the
PT_INTERP program header is now avaiable via a getter. The dynamic
loader program will want to check that this matches its name, for extra
shenanigans checking.
