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Debug Info: One more bitfield bugfix. While yesterday's r240853 fixed 

the DW_AT_bit_offset computation, the byte offset is in fact also
endian-dependent as it needs to point to the storage unit containing the
most-significant bit of the the bitfield.
I'm so looking forward to emitting the endian-agnostic DWARF 3 version
instead.

llvm-svn: 240890
This commit is contained in:
Adrian Prantl 2015-06-27 20:12:43 +00:00
parent 43899d44c2
commit 57c7a62b97
2 changed files with 22 additions and 17 deletions
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37
llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
View File

@ -1346,9 +1346,9 @@ void DwarfUnit::constructMemberDIE(DIE &Buffer, const DIDerivedType *DT) {
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.
// The DWARF 2 DW_AT_bit_offset is counting the bits between the most
// significant bit of the aligned storage unit containing the bit field to
// the most significan bit of the bit field.
//
// FIXME: DWARF 4 states that DW_AT_data_bit_offset (which
// counts from the beginning, regardless of endianness) should
@ -1361,24 +1361,29 @@ void DwarfUnit::constructMemberDIE(DIE &Buffer, const DIDerivedType *DT) {
// | ... |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
// |<---- Offset --->| | |<--->|
// | | | | \_ DW_AT_bit_offset (little endian)
// | |<--->| |
// |<--big-e.->| \_ StartBitOffset = DW_AT_bit_offset (big endian)
// | ^ | = DW_AT_data_bit_offset (biendian)
// | OffsetInBytes |
// | v |
// |<----little-endian---->|
uint64_t Offset = DT->getOffsetInBits();
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;
// The byte offset of the field's aligned storage unit inside the struct.
OffsetInBytes = (Offset - StartBitOffset) / 8;
// OffsetInBytes is the byte offset of the field's aligned storage unit
// inside the struct.
uint64_t DwarfBitOffset;
if (Asm->getDataLayout().isLittleEndian()) {
DwarfBitOffset = OffsetToAlignment(Offset + Size, Align);
OffsetInBytes = ((Offset + Size) & AlignMask) / 8;
} else {
DwarfBitOffset = StartBitOffset;
OffsetInBytes = (Offset - StartBitOffset) / 8;
}
addUInt(MemberDie, dwarf::DW_AT_bit_offset, None, DwarfBitOffset);
} else
// This is not a bitfield.

2
llvm/test/DebugInfo/ARM/bitfield.ll
View File

@ -14,7 +14,7 @@
; CHECK: DW_AT_byte_size {{.*}} (0x04)
; CHECK: DW_AT_bit_size {{.*}} (0x1c)
; CHECK: DW_AT_bit_offset {{.*}} (0x18)
; CHECK: DW_AT_data_member_location {{.*}}00
; CHECK: DW_AT_data_member_location {{.*}}04
target datalayout = "e-m:o-p:32:32-f64:32:64-v64:32:64-v128:32:128-a:0:32-n32-S32"
target triple = "thumbv7-apple-ios"