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See #363. Please file issues rather than making TODO comments.
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Makes linker functions have small error sets, required to report
diagnostics properly rather than having a massive error set that has a
lot of codes.
Other linker implementations are not ported yet.
Also the branch is not passing semantic analysis yet.
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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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This is necessary since isGnuLibC() is true for hurd, so we need to be able to
represent a glibc version for it.
Also add an Os.TaggedVersionRange.gnuLibCVersion() convenience function.
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The old isARM() function was a portability trap. With the name it had, it seemed
like the obviously correct function to use, but it didn't include Thumb. In the
vast majority of cases where someone wants to ask "is the target Arm?", Thumb
*should* be included.
There are exactly 3 cases in the codebase where we do actually need to exclude
Thumb, although one of those is in Aro and mirrors a check in Clang that is
itself likely a bug. These rare cases can just add an extra isThumb() check.
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Once we upgrade to LLVM 20, these should be lowered verbatim rather than to
simply musl. Similarly, the special case in llvmMachineAbi() should go away.
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Primarily, this moves linker input parsing from flush() into the linker
task queue, which is executed simultaneously with the frontend.
I also made it avoid redundantly opening the same archive file N times
for each object file inside. Furthermore, hard code fixed buffer stream
rather than using a generic stream type.
Finally, I fixed the error handling of the Wasm.Archive.parse function.
Please pay attention to this pattern of returning a struct rather than
accepting a mutable struct as an argument. This ensures function-level
atomicity and makes resource management straightforward.
Deletes the file and path fields from Archive and Object.
Removed a well-meaning but ultimately misguided suggestion about how to
think about ZigObject since thinking about it that way has led to
problematic anti-DOD patterns.
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fixes e567abb339e1edaf5a3c86fe632522a3b8005275 "rework linker inputs"
closes https://github.com/ziglang/zig/issues/21801
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it is incredible how many bad ideas glibc is bundled into one project.
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using name as tie-breaker.
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By making it a field of link.Elf, it is now accessible without a data
dependency on `files`, fixing a race condition with the codegen thread
and linker thread.
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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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The compiler defaults this value to off so that users whose system
shared libraries are all ELF files don't have to pay the cost of
checking every file to find out if it is a text file instead.
When a GNU ld script is encountered, the error message instructs users
about the CLI flag that will immediately solve their problem.
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along with the relevant logic, making the libraries within subject to
the same search criteria as all the other libraries.
this unfortunately means doing file system access on all .so files when
targeting ELF to determine if they are linker scripts, however, I have a
plan to address this.
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this allows it to be used by the frontend
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The only use of this has nothing to do with the OS tag.
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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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`link.Elf.merge_section.MergeSection` -> `link.Elf.Merge.Section`
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so they cannot be forgotten when updating them after sorting them.
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Adds type safety for program header indexes.
Reduce the amount of state sortPhdrs has access to, helping make the
data dependencies clear.
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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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When resolving and writing atoms to file, we may add dynamic relocs
to the output buffer so clear the buffers before that happens.
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This way we can track if we need to redo the object parsing or not.
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