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Debug Info: Fix a bug in the DW_AT_bit_offset calculation that would

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result in negative offsets and attempt a better job at documenting
the algorithm.

rdar://21082998

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@240853 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Adrian Prantl
2015-06-26 23:31:27 +00:00
parent 340d78d52d
commit 60bd365f59
2 changed files with 72 additions and 12 deletions
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39
lib/CodeGen/AsmPrinter/DwarfUnit.cpp
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@@ -1345,7 +1345,7 @@ void DwarfUnit::constructMemberDIE(DIE &Buffer, const DIDerivedType *DT) {
// Handle bitfield, assume bytes are 8 bits.
addUInt(MemberDie, dwarf::DW_AT_byte_size, None, FieldSize/8);
addUInt(MemberDie, dwarf::DW_AT_bit_size, None, Size);
//
// The DWARF 2 DW_AT_bit_offset is counting the bits between
// the high end of the aligned storage unit containing the bit
// field to the high end of the bit field.
@@ -1353,21 +1353,36 @@ void DwarfUnit::constructMemberDIE(DIE &Buffer, const DIDerivedType *DT) {
// FIXME: DWARF 4 states that DW_AT_data_bit_offset (which
// counts from the beginning, regardless of endianness) should
// be used instead.
//
//
// Struct Align Align Align
// v v v v
// +-----------+-----*-----+-----*-----+--
// | ... |b1|b2|b3|b4|
// +-----------+-----*-----+-----*-----+--
// | | |<-- Size ->| |
// |<---- Offset --->| |<--->|
// | | | \_ DW_AT_bit_offset (little endian)
// | |<--->|
// |<--------->| \_ StartBitOffset = DW_AT_bit_offset (big endian)
// \ = DW_AT_data_bit_offset (biendian)
// \_ OffsetInBytes
uint64_t Offset = DT->getOffsetInBits();
uint64_t AlignMask = ~(DT->getAlignInBits() - 1);
uint64_t HiMark = (Offset + FieldSize) & AlignMask;
uint64_t FieldOffset = (HiMark - FieldSize);
Offset -= FieldOffset;
uint64_t Align = DT->getAlignInBits() ? DT->getAlignInBits() : FieldSize;
uint64_t AlignMask = ~(Align - 1);
// The bits from the start of the storage unit to the start of the field.
uint64_t StartBitOffset = Offset - (Offset & AlignMask);
// The endian-dependent DWARF 2 offset.
uint64_t DwarfBitOffset = Asm->getDataLayout().isLittleEndian()
? OffsetToAlignment(Offset + Size, Align)
: StartBitOffset;
// Maybe we need to work from the other end.
if (Asm->getDataLayout().isLittleEndian())
Offset = FieldSize - (Offset + Size);
addUInt(MemberDie, dwarf::DW_AT_bit_offset, None, Offset);
OffsetInBytes = FieldOffset >> 3;
// The byte offset of the field's aligned storage unit inside the struct.
OffsetInBytes = (Offset - StartBitOffset) / 8;
addUInt(MemberDie, dwarf::DW_AT_bit_offset, None, DwarfBitOffset);
} else
// This is not a bitfield.
OffsetInBytes = DT->getOffsetInBits() >> 3;
OffsetInBytes = DT->getOffsetInBits() / 8;
if (DD->getDwarfVersion() <= 2) {
DIELoc *MemLocationDie = new (DIEValueAllocator) DIELoc;