[2019-10] [metadata] Size 0 Blob heap is ok when resolving assembly refs #18338
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Sometimes ILasm can produce images with a Blob heap of size 0. In cases where we're loading assembly references from such an image, the hash (which is optional) can be at index = 0 and the Blob heap size is also 0. Also: add the hash value to the output of `monodis --assemblyref`
ECMA 335 II.24.2.4 says that the user string and blob heaps should have an entry at index 0 consisting of the single byte 0. However .NET Framework (and .NET Core) ilasm will entirely omit the Blob heap (that is, create a blob heap entry of size 0) if it is not needed. This PR changes Mono's ILASM to emit the initial byte on demand only if one of the MetaDataStream.Add() methods is called. Otherwise we will also emit a stream of size 0. This is needed to compile some test cases.
Depends on ILASM that can emit a size 0 Blob heap
And a comment explaining how it is likely to be triggered. If the assembly is reasonable the caller of mono_metadata_blob_heap should be updated to use mono_metadata_blob_heap_null_ok instead
lambdageek
approved these changes
Jan 3, 2020
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Sometimes, ILasm apparently can produce images with a size 0 Blob heap. In cases where we're loading assembly references from such an image, the hash (which is optional) can be at index = 0 and the Blob heap size is also 0.
Also: add the hash value to the output of
monodis --assemblyrefAlso: patch PEAPI (used by mono's
ilasm) to emit a size 0 Blob heap if no blobs are added. Previously it would unconditionally emit the index 0 entry (a single zero byte - required by ECMA 335 II.24.2.) Now it will only emit the index 0 entry only if the MetaDataStream.Add methods are called.Related to #10332
Backport of #18313.
/cc @lambdageek