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Debug Info: Restore the pre-r240853 behavior for DWARF2 bitfields.

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The DWARF2 specification of DW_AT_bit_offset is ambiguous for
little-endian machines, but by restoring to the old behavior
we match what debuggers expect and what other popular compilers
generate.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267896 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Adrian Prantl 2016-04-28 15:37:52 +00:00
parent 9ed561fe46
commit ee1e0438b6
2 changed files with 10 additions and 24 deletions
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32
lib/CodeGen/AsmPrinter/DwarfUnit.cpp
View File

@ -1407,30 +1407,16 @@ void DwarfUnit::constructMemberDIE(DIE &Buffer, const DIDerivedType *DT) {
if (DD->getDwarfVersion() >= 4)
addUInt(MemberDie, dwarf::DW_AT_data_bit_offset, None, Offset);
else {
//
// 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.
//
// 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
// The endian-dependent DWARF 2 offset.
uint64_t DwarfBitOffset = Asm->getDataLayout().isLittleEndian()
? OffsetToAlignment(Offset + Size, Align)
: StartBitOffset;
uint64_t HiMark = (Offset + FieldSize) & AlignMask;
uint64_t FieldOffset = (HiMark - FieldSize);
Offset -= FieldOffset;
addUInt(MemberDie, dwarf::DW_AT_bit_offset, None, DwarfBitOffset);
// 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;
}
} else
// This is not a bitfield.

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

@ -13,7 +13,7 @@
; CHECK: DW_AT_name {{.*}} "reserved"
; CHECK: DW_AT_byte_size {{.*}} (0x04)
; CHECK: DW_AT_bit_size {{.*}} (0x1c)
; CHECK: DW_AT_bit_offset {{.*}} (0x18)
; CHECK: DW_AT_bit_offset {{.*}} (0xfffffffffffffff8)
; CHECK: DW_AT_data_member_location {{.*}}00
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"