* apply late symbol resolution for globals - instead of resolving
the exact location of a symbol in locals, globals or undefs,
we postpone the exact resolution until we have a full picture
for relocation resolution.
* fixup stubs to defined symbols - this is currently a hack rather
than a final solution. I'll need to work out the details to make
it more approachable. Currently, we preemptively create a stub
for a lazy bound global and fix up stub offsets in stub helper
routine if the global turns out to be undefined only. This is quite
wasteful in terms of space as we create stub, stub helper and lazy ptr
atoms but don't use them for defined globals.
* change log scope to .link for macho.
* remove redundant code paths from Object and Atom.
* drastically simplify the contents of Relocation struct (i.e., it is
now a simple superset of macho.relocation_info), clean up relocation
parsing and resolution logic.
* In watch mode, when changing the C source, we will trigger complete
relinking of objects, dylibs and archives (atoms coming from the
incremental updates stay put however). This means, we need to undo
metadata populated when linking in objects, archives and dylibs.
* Remove unused splitting section into atoms bit. This optimisation
will probably be best rewritten from scratch once self-hosted
matures so parking the idea for now. Also, for easier management
of atoms spawned from the Object file, keep the atoms subgraph as
part of the Object file struct.
* Remove obsolete ref to static initializers in object struct.
* Implement handling of global symbol collision in updateDeclExports.
This is particularly relevant for x86_64 and C++ when relocating
StaticInit sections containing static initializers machine code.
Then, in case of SIGNED_X relocations, it is necessary to have the
full image of the VM address layout of the sections in the object
file as this is how the addend needs to be adjusted for non-extern
relocations.
Also, calculate non-extern, section offset based addends for SIGNED
and UNSIGNED relocations on x86_64 upfront as an offset wrt to the
target symbol representing position of the section/atom within the
final artifact.
Instead of checking for stage1 at every callsite, move the logic
inside `allocateAtom`. This is fine since this logic will disappear
anyhow once I add expanding and shifting segments and sections.
This commit makes it possible to combine self-hosted with a pre-compiled
C object file, e.g.:
```
zig-out/bin/zig build-exe hello.zig add.o
```
where `add.o` is a pre-compiled C object file.
instead, immediately transfer ownership to MachO struct. Also, revert
back to try-ok-fail parsing approach of objects, archives, and dylibs.
It seems easier to try and fail than check if the file *is* of a
certain type given that a dylib may be a stub and parsing yaml
twice in a row seems very wasteful.
Hint for the future: if we optimise yaml/TAPI parsing, this approach
may be rethought!
instead, pass it in functions that require it. Also, when parsing
relocs, make Object part of the context struct where we pass in
additional goodies such as `*MachO` or `*Allocator`.
then, when sorting sections within segments, clear and redo the
ordinals since we re-apply them to symbols anyway. It is vital
to have the ordinals consistent with parsing and resolving relocs
however.
Previously, we'd filter the nlists assuming they were correctly
ordered by type: local < extern defined < undefined within the
object's symbol table but this doesn't seem to be guaranteed,
therefore, we sort by type and address in one go, and filter
defined from undefined afterwards.
For the time being, until we rewrite how atoms are handled across
linkers, store two tables in the MachO linker: one for TextBlocks
directly created and managed by the linker, and one for TextBlocks
that were spawned by Module.Decl. This allows for correct memory
clean up after linking is done.
It makes sense to have them as a dependent type since they only ever
deal with TextBlocks. Simplify Relocations to rely on symbol indices
and symbol resolver rather than pointers.
Also, add a solution to a degenerate case where on x86_64 a relocation
refers to a cell in a section via section start address even though
a symbol exists. In such case, make the section spawned symbol an alias
of the actual symbol.
section's alignment serving as the maximum alignment that
can be seen in this particular section. However, TextBlocks are
still allowed to have at most that alignment.
