From 579264bd5999931aea53b8e9bb7687f93a828247 Mon Sep 17 00:00:00 2001 From: Zachary Turner Date: Thu, 6 Dec 2018 16:55:00 +0000 Subject: Support skewed stream arrays. VarStreamArray was built on the assumption that it is backed by a StreamRef, and offset 0 of that StreamRef is the first byte of the first record in the array. This is a logical and intuitive assumption, but unfortunately we have use cases where it doesn't hold. Specifically, a PDB module's symbol stream is prefixed by 4 bytes containing a magic value, and the first byte of record data in the array is actually at offset 4 of this byte sequence. Previously, we would just truncate the first 4 bytes and then construct the VarStreamArray with the resulting StreamRef, so that offset 0 of the underlying stream did correspond to the first byte of the first record, but this is problematic, because symbol records reference other symbol records by the absolute offset including that initial magic 4 bytes. So if another record wants to refer to the first record in the array, it would say "the record at offset 4". This led to extremely confusing hacks and semantics in loading code, and after spending 30 minutes trying to get some math right and failing, I decided to fix this in the underlying implementation of VarStreamArray. Now, we can say that a stream is skewed by a particular amount. This way, when we access a record by absolute offset, we can use the same values that the records themselves contain, instead of having to do fixups. Differential Revision: https://reviews.llvm.org/D55344 llvm-svn: 348499 --- llvm/lib/DebugInfo/PDB/Native/ModuleDebugStream.cpp | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) (limited to 'llvm/lib/DebugInfo/PDB/Native/ModuleDebugStream.cpp') diff --git a/llvm/lib/DebugInfo/PDB/Native/ModuleDebugStream.cpp b/llvm/lib/DebugInfo/PDB/Native/ModuleDebugStream.cpp index 6464b85982e..5ff7c1574dd 100644 --- a/llvm/lib/DebugInfo/PDB/Native/ModuleDebugStream.cpp +++ b/llvm/lib/DebugInfo/PDB/Native/ModuleDebugStream.cpp @@ -47,7 +47,8 @@ Error ModuleDebugStreamRef::reload() { if (auto EC = Reader.readInteger(Signature)) return EC; - if (auto EC = Reader.readSubstream(SymbolsSubstream, SymbolSize - 4)) + Reader.setOffset(0); + if (auto EC = Reader.readSubstream(SymbolsSubstream, SymbolSize)) return EC; if (auto EC = Reader.readSubstream(C11LinesSubstream, C11Size)) return EC; @@ -55,8 +56,8 @@ Error ModuleDebugStreamRef::reload() { return EC; BinaryStreamReader SymbolReader(SymbolsSubstream.StreamData); - if (auto EC = - SymbolReader.readArray(SymbolArray, SymbolReader.bytesRemaining())) + if (auto EC = SymbolReader.readArray( + SymbolArray, SymbolReader.bytesRemaining(), sizeof(uint32_t))) return EC; BinaryStreamReader SubsectionsReader(C13LinesSubstream.StreamData); @@ -98,9 +99,7 @@ ModuleDebugStreamRef::symbols(bool *HadError) const { } CVSymbol ModuleDebugStreamRef::readSymbolAtOffset(uint32_t Offset) const { - // Offsets include the size of the 4-byte magic at the beginning, but lookup - // doesn't take that into account, so subtract it here. - auto Iter = SymbolArray.at(Offset - 4); + auto Iter = SymbolArray.at(Offset); assert(Iter != SymbolArray.end()); return *Iter; } -- cgit v1.2.3