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[Serialization] Load swiftmodule files as volatile to avoid mmap #33001

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Merged
merged 2 commits into from
Jul 21, 2020
Merged

[Serialization] Load swiftmodule files as volatile to avoid mmap #33001

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[Serialization] Load swiftmodule files as volatile to avoid mmap
xymus Jul 18, 2020
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[Serialization] Add more context to why we load swiftmodule files as …
xymus Jul 21, 2020
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19 changes: 18 additions & 1 deletion lib/Serialization/SerializedModuleLoader.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -347,8 +347,25 @@ std::error_code SerializedModuleLoaderBase::openModuleFile(
}

// Actually load the file and error out if necessary.
//
// Use the default arguments except for IsVolatile. Force avoiding the use of
// mmap to workaround issues on NFS when the swiftmodule file loaded changes
// on disk while it's in use.
//
// In practice, a swiftmodule file can chane when a client uses a
// swiftmodule file from a framework while the framework is recompiled and
// installed over existing files. Or when many processes rebuild the same
// module interface.
//
// We have seen these scenarios leading to deserialization errors that on
// the surface look like memory corruption.
//
// rdar://63755989
llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> ModuleOrErr =
FS.getBufferForFile(ModulePath);
FS.getBufferForFile(ModulePath,
/*FileSize=*/-1,
/*RequiresNullTerminator=*/true,
/*IsVolatile=*/true);
if (!ModuleOrErr)
return ModuleOrErr.getError();

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