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[lld] check cache before real_path in loadDylib #140791

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[lld] check cache before real_path in loadDylib #140791

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26 changes: 20 additions & 6 deletions lld/MachO/DriverUtils.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -229,19 +229,31 @@ static DenseMap<CachedHashStringRef, DylibFile *> loadedDylibs;

DylibFile *macho::loadDylib(MemoryBufferRef mbref, DylibFile *umbrella,
bool isBundleLoader, bool explicitlyLinked) {
// Frameworks can be found from different symlink paths, so resolve
// symlinks before looking up in the dylib cache.
SmallString<128> realPath;
std::error_code err = fs::real_path(mbref.getBufferIdentifier(), realPath);
CachedHashStringRef path(!err ? uniqueSaver().save(StringRef(realPath))
: mbref.getBufferIdentifier());
CachedHashStringRef path(mbref.getBufferIdentifier());
DylibFile *&file = loadedDylibs[path];
if (file) {
if (explicitlyLinked)
file->setExplicitlyLinked();
return file;
}

// Frameworks can be found from different symlink paths, so resolve
// symlinks and look up in the dylib cache.
DylibFile *&realfile = file;
SmallString<128> realPath;
std::error_code err = fs::real_path(mbref.getBufferIdentifier(), realPath);
if (!err) {
CachedHashStringRef resolvedPath(uniqueSaver().save(StringRef(realPath)));
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Suggested change
CachedHashStringRef resolvedPath(uniqueSaver().save(StringRef(realPath)));
CachedHashStringRef resolvedPath(uniqueSaver().save(realPath.str()));

realfile = loadedDylibs[resolvedPath];
if (realfile) {
if (explicitlyLinked)
realfile->setExplicitlyLinked();

file = realfile;
return realfile;
}
}

DylibFile *newFile;
file_magic magic = identify_magic(mbref.getBuffer());
if (magic == file_magic::tapi_file) {
Expand All @@ -253,6 +265,7 @@ DylibFile *macho::loadDylib(MemoryBufferRef mbref, DylibFile *umbrella,
}
file =
make<DylibFile>(**result, umbrella, isBundleLoader, explicitlyLinked);
realfile = file;
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In the common case we have

DylibFile *&file = loadedDylibs[path];
DylibFile *&realfile = file;

Then what happens on this line? It does a load and a store to the same address? I'm sure it does the right thing it just looks funny to me.

Also, if we set file later in the future, how can we make sure to not forget to also set realfile? Is there a better way of doing this?

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@rmaz rmaz May 22, 2025 •
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Then what happens on this line? It does a load and a store to the same address?

Thats what I thought would happen, yes.

Also, if we set file later in the future, how can we make sure to not forget to also set realfile? Is there a better way of doing this?

What would you suggest? Ultimately we have 2 cache pointers, that may or may not point to the same thing, and we need to update them.


// parseReexports() can recursively call loadDylib(). That's fine since
// we wrote the DylibFile we just loaded to the loadDylib cache via the
Expand All @@ -268,6 +281,7 @@ DylibFile *macho::loadDylib(MemoryBufferRef mbref, DylibFile *umbrella,
magic == file_magic::macho_executable ||
magic == file_magic::macho_bundle);
file = make<DylibFile>(mbref, umbrella, isBundleLoader, explicitlyLinked);
realfile = file;

// parseLoadCommands() can also recursively call loadDylib(). See comment
// in previous block for why this means we must copy `file` here.
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