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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;

45
test/DebugInfo/ARM/bitfield.ll Normal file
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@ -0,0 +1,45 @@
; RUN: %llc_dwarf -O0 -filetype=obj -o %t.o %s
; RUN: llvm-dwarfdump -debug-dump=info %t.o | FileCheck %s
; REQUIRES: object-emission
;
; Generated from:
; struct {
; char c;
; int : 4;
; int reserved : 28;
; } a;
;
; CHECK: DW_TAG_member
; 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_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"
%struct.anon = type { i8, [5 x i8] }
@a = common global %struct.anon zeroinitializer, align 1
!llvm.dbg.cu = !{!0}
!llvm.module.flags = !{!11, !12, !13, !14, !15}
!llvm.ident = !{!16}
!0 = !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 3.7.0 (trunk 240548) (llvm/trunk 240554)", isOptimized: false, runtimeVersion: 0, emissionKind: 1, enums: !2, retainedTypes: !2, subprograms: !2, globals: !3, imports: !2)
!1 = !DIFile(filename: "test.i", directory: "/")
!2 = !{}
!3 = !{!4}
!4 = !DIGlobalVariable(name: "a", scope: !0, file: !1, line: 5, type: !5, isLocal: false, isDefinition: true, variable: %struct.anon* @a)
!5 = !DICompositeType(tag: DW_TAG_structure_type, file: !1, line: 1, size: 48, align: 8, elements: !6)
!6 = !{!7, !9}
!7 = !DIDerivedType(tag: DW_TAG_member, name: "c", scope: !5, file: !1, line: 2, baseType: !8, size: 8, align: 8)
!8 = !DIBasicType(name: "char", size: 8, align: 8, encoding: DW_ATE_signed_char)
!9 = !DIDerivedType(tag: DW_TAG_member, name: "reserved", scope: !5, file: !1, line: 4, baseType: !10, size: 28, align: 32, offset: 12)
!10 = !DIBasicType(name: "int", size: 32, align: 32, encoding: DW_ATE_signed)
!11 = !{i32 2, !"Dwarf Version", i32 2}
!12 = !{i32 2, !"Debug Info Version", i32 3}
!13 = !{i32 1, !"wchar_size", i32 4}
!14 = !{i32 1, !"min_enum_size", i32 4}
!15 = !{i32 1, !"PIC Level", i32 2}
!16 = !{!"clang version 3.7.0 (trunk 240548) (llvm/trunk 240554)"}