Previously, we would get a pointer to a slot in the symbol table,
apply changes to the symbol, and return the pointer. This however
didn't take into account that the symbol table may be moved in memory
in-between the modification and return from the function (`fn placeDecl`).
Prior to my rewrite, this was not possible within the body of the said
function. However, my rewrite revamped how we allocate GOT atoms and
their matching symtab indexes, which now may cause a move in memory
of the container.
In x86_64 relocs, it can so happen that the compiler
refers to the same atom by both the actual assigned symbol
and the start of the section. In this case, we need to
link the two together so add an alias.
Now, each object file will store a mutable table of symbols that it
defines. Upon symbol resolution between object files, the symbol
will be updated with a globally allocated section ordinal and address
in virtual memory. If the object defines a globally available symbol,
its location only (comprising of the symbol index and object index)
will be stored in the globals map for easy access when relocating, etc.
This approach cleans up the symbol management significantly, and matches
the status quo used in zld/ELF.
Additionally, this makes scoping symbol stabs easier too as they are
now naturally contained within each object file.
When lowering a struct type to an LLVM struct type, keep track of
whether there are any underaligned fields. If so, then make it a packed
llvm struct. This works because we already insert manual padding bytes
regardless.
We could unconditionally use an LLVM packed struct; the reason we bother
checking for underaligned fields is that it is a conservative choice, in
case LLVM handles packed structs less optimally. A future improvement
could simplify this code by unconditionally using packed LLVM structs
and then make sure measure perf is unaffected.
closes#12190
`validateExternType` does not require the type to be resolved so we can
check it earlier. Only doing it in `resolveTypeFully` lead to worse or
missing compile errors.
