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[Runtime] Use the properly resolved tag when adding offset after resolving relative pointers in layout strings

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The tag was overwritten after resolve when a prior field caused a non-zero offset. This then caused the runtime to treat is a relative instead of an absolute pointer, causing invalid pointers to be dereferenced.
This commit is contained in:
Dario Rexin
2023-07-24 09:36:26 -07:00
parent 81edb298bb
commit 10685367ce
2 changed files with 37 additions and 2 deletions
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4
stdlib/public/runtime/Metadata.cpp
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@@ -2827,9 +2827,9 @@ void swift::_swift_addRefCountStringForMetatype(LayoutStringWriter &writer,
}
if (offset) {
LayoutStringReader tagReader {writer.layoutStr, writer.offset};
auto writerOffsetCopy = writer.offset;
reader.offset = layoutStringHeaderSize;
auto firstTagAndOffset = reader.readBytes<uint64_t>();
auto firstTagAndOffset = tagReader.readBytes<uint64_t>();
firstTagAndOffset += offset;
writer.writeBytes(firstTagAndOffset);
writer.offset = writerOffsetCopy;