This adds the following for passthrough to lld:
- `--print-gc-sections`
- `--print-icf-sections`
- `--print-map`
I am not adding these to the cache manifest, since it does not change
the produced artifacts.
Tested with an example from #11398: it successfully prints the resulting
map and the GC'd sections.
If there are zerofill sections, the loader may copy the contents of
the physical space in file directly into memory and attach that to
the zerofill section. This is a performance optimisation in the loader
but requires us, the linker, to properly zero-out any space between
__DATA and __LINKEDIT segments in file. This is of course completely
skipped if there are no zerofill sections present.
This is a temporary workaround to an unclear platform-dependence
behavior we have in libstd for `std.fs.File` abstraction. See
https://github.com/ziglang/zig/issues/12783 for more information.
As far as I can see, unlike with MachO, we don't have any stubs
helper routines available and need to load a bound pointer into
a register to then call it.
Although the wasm-linker previously already supported
debug information in incremental-mode, this was no longer
working as-is with the addition of supporting object-file-parsed
debug information. This commit implements the Zig-created debug information
structure from scratch which is a lot more robust and also allows
being linked with debug information from other object files.
When linking a Zig-compilation with an object file,
we allow mixing the debug atoms to make sure debug
information is preserved from object files. By default,
we now always initialize all debug sections if the `strip` flag
is unset.
This also fixes relocations for debug information as previously
the offset of an atom wasn't calculated, and neither was the code
size itself which meant that debug lines were off and file names
from other object files were missing.
Previously we used single arraylists for each debug section for debug
information that was generated from Zig code. (e.i. `Module` is available).
This information is now stored in Atoms, similarly to debug information
from object files. This will allow us to link them together and resolve
debug relocations.
This correctly performs a relocation for debug sections.
The result is that the wasm-linker can now correctly create
a binary from object files while preserving all debug information.
We now link relocatable debug sections with the correct
section symbol and then allocate and resolve the debug atoms
before writing them into the final binary.
Although this does perform the relocation, the actual relocations
are not done correctly yet.
Rather than storing the name of a debug section into the structure
`RelocatableData`, we use the `index` field as an offset into the
debug names table. This means we do not have to store an extra 16 bytes
for non-debug sections which can be massive for object files where each
data symbol has its own data section. The name of a debug section
can then be retrieved again when needed by using the offset and
then reading until the 0-delimiter.
This means we can request ASLR on by default as other COFF linkers
do. Currently, we write the base relocations in bulk, however,
given that there is a mechanism for padding in place in PE/COFF
I believe there might be room for making it an incremental operation
(write base relocation whenever we add/update a pointer that would
require it).
This also fixes performing relocations for data symbols
of which the target symbol exists in an external object file.
We do this by checking if the target symbol was discarded,
and if so: get the new location so that we can find the
corresponding atom that belongs to said new location. Previously
it would always assume the symbol would live in the same file
as the atom/symbol that is doing the relocation.
Generate symbols for extern variables and try to resolve them.
Unresolved 'data' symbols generate an error as they cannot be
exported from the Wasm runtime into a Wasm module. This means,
they can only be resolved by other object files such as from other
Zig or C code compiled to Wasm.
Given that COFF will want to support PIC from ground-up, there is no
point in leaving outdated code for COFF in other backends such as
arm or aarch64. Instead, when we are ready to look into those, we
can start figuring out what to add and where.
This is not technically correct, but given that we are not yet able
to link against the CRT, it's a good default until then.
Add basic logging of generated symbol table in the linker.
