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missing `extern` on a struct.
but also all these instances that call pwriteAll with a `@ptrCast` are
endianness bugs.
this should be changed to use File.Writer and call writeSliceEndian
instead.
this commit fixes one immediate problem but does not fix everything.
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I haven't actually found any documentation about these, but apparently groups
aren't always comdats.
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The goals of this branch are to:
* compile faster when using the wasm linker and backend
* enable saving compiler state by directly copying in-memory linker
state to disk.
* more efficient compiler memory utilization
* introduce integer type safety to wasm linker code
* generate better WebAssembly code
* fully participate in incremental compilation
* do as much work as possible outside of flush(), while continuing to do
linker garbage collection.
* avoid unnecessary heap allocations
* avoid unnecessary indirect function calls
In order to accomplish this goals, this removes the ZigObject
abstraction, as well as Symbol and Atom. These abstractions resulted
in overly generic code, doing unnecessary work, and needless
complications that simply go away by creating a better in-memory data
model and emitting more things lazily.
For example, this makes wasm codegen emit MIR which is then lowered to
wasm code during linking, with optimal function indexes etc, or
relocations are emitted if outputting an object. Previously, this would
always emit relocations, which are fully unnecessary when emitting an
executable, and required all function calls to use the maximum size LEB
encoding.
This branch introduces the concept of the "prelink" phase which occurs
after all object files have been parsed, but before any Zcu updates are
sent to the linker. This allows the linker to fully parse all objects
into a compact memory model, which is guaranteed to be complete when Zcu
code is generated.
This commit is not a complete implementation of all these goals; it is
not even passing semantic analysis.
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According to a comment in mold, this is the expected (and desired)
condition by the linkers, except for some architectures (RISCV and
Loongarch) where this condition does not have to upheld.
If you follow the changes in this patch and in particular doc comments
I have linked the comment/code in mold that explains and implements
this.
I have also modified `testEhFrameRelocatable` test to now test both
cases such that `zig ld -r a.o b.o -o c.o` and `zig ld -r b.o a.o -o
d.o`. In both cases, `c.o` and `d.o` should produce valid object
files which was not the case before this patch.
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unstable sort is always better if you have no ties
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from link.Elf, so that they can be used earlier in the pipeline
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* Compilation.objects changes to Compilation.link_inputs which stores
objects, archives, windows resources, shared objects, and strings
intended to be put directly into the dynamic section. Order is now
preserved between all of these kinds of linker inputs. If it is
determined the order does not matter for a particular kind of linker
input, that item should be moved to a different array.
* rename system_libs to windows_libs
* untangle library lookup from CLI types
* when doing library lookup, instead of using access syscalls, go ahead
and open the files and keep the handles around for passing to the
cache system and the linker.
* during library lookup and cache file hashing, use positioned reads to
avoid affecting the file seek position.
* library directories are opened in the CLI and converted to Directory
objects, warnings emitted for those that cannot be opened.
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Make shared_objects a StringArrayHashMap so that deduping does not
need to happen in flush. That deduping code also was using an O(N^2)
algorithm, which is not allowed in this codebase. There is another
violation of this rule in resolveSymbols but this commit does not
address it.
This required reworking shared object parsing, breaking it into
independent components so that we could access soname earlier.
Shared object parsing had a few problems that I noticed and fixed in
this commit:
* Many instances of incorrect use of align(1).
* `shnum * @sizeOf(elf.Elf64_Shdr)` can overflow based on user data.
* `@divExact` can cause illegal behavior based on user data.
* Strange versyms logic that wasn't present in mold nor lld. The logic
was not commented and there is no git blame information in ziglang/zig
nor kubkon/zld. I changed it to match mold and lld instead.
* Use of ArrayList for slices of memory that are never resized.
* finding DT_VERDEFNUM in a different loop than finding DT_SONAME.
Ultimately I think we should follow mold's lead and ignore this
integer, relying on null termination instead.
* Doing logic based on VER_FLG_BASE rather than ignoring it like mold
and LLD do. No comment explaining why the behavior is different.
* Mutating the original ELF symbols rather than only storing the mangled
name on the new Symbol struct.
I noticed something that I didn't try to address in this commit: Symbol
stores a lot of redundant information that is already present in the ELF
symbols. I suspect that the codebase could benefit from reworking Symbol
to not store redundant information.
Additionally:
* Add some type safety to std.elf.
* Eliminate 1-3 file system reads for determining the kind of input
files, by taking advantage of file name extension and handling error
codes properly.
* Move more error handling methods to link.Diags and make them
infallible and thread-safe
* Make the data dependencies obvious in the parameters of
parseSharedObject. It's now clear that the first two steps (Header and
Parsed) can be done during the main Compilation pipeline, rather than
waiting for flush().
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By organizing linker diagnostics into this struct, it becomes possible
to share more code between linker backends, and more importantly it
becomes possible to pass only the Diag struct to some functions, rather
than passing the entire linker state object in. This makes data
dependencies more obvious, making it easier to rearrange code and to
multithread.
Also fix MachO code abusing an atomic variable. Not only was it using
the wrong atomic operation, it is unnecessary additional state since
the state is already being protected by a mutex.
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In order to reduce the logic that happens in flush() we need to see
which data is being accessed by all this logic, so we can see which
operations depend on each other.
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so they cannot be forgotten when updating them after sorting them.
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Embrace the Path abstraction, doing more operations based on directory
handles rather than absolute file paths. Most of the diff noise here
comes from this one.
Fix sorting of crtbegin/crtend atoms. Previously it would look at all
path components for those strings.
Make the C runtime path detection partially a pure function, and move
some logic to glibc.zig where it belongs.
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flush() must not do anything more than necessary. Determining the type
of input files must be done only once, before flush. Fortunately, we
don't even need any file system accesses to do this since that
information is statically known in most cases, and in the rest of the
cases can be determined by file extension alone.
This commit also updates the nearby code to conform to the convention
for error handling where there is exactly one error code to represent
the fact that error messages have already been emitted. This had the
side effect of improving the error message for a linker script parse
error.
"positionals" is not a linker concept; it is a command line interface
concept. Zig's linker implementation should not mention "positionals".
This commit deletes that array list in favor of directly making function
calls, eliminating that heap allocation during flush().
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relocatable mode
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elf: cleanups, cleanups, cleanups
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This is in preparation for incremental and actually being able to debug
executables built by the x86_64 backend.
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