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[WIP][DebugInfo] Lazily parse debug_loclist offsets 

Parsing DWARFv5 debug_loclist offsets when a CU is parsed is weighing
down memory usage of symbolizers that don't need to parse this data at
all. There's not much benefit to caching these anyway - since they are
O(1) lookup and reading once you know where the offset list starts (and
can do bounds checking with the offset list size too).

In general, I think it might be time to start paying down some of the
technical debt of loc/loclist/range/rnglist parsing to try to unify it a
bit more.

eg:

* Currently DWARFUnit has: RangeSection, RangeSectionBase, LocSection,
  LocSectionBase, LocTable, RngListTable, LoclistTableHeader (be nice if
  these were all wrapped up in two variables - one for loclists, one for
  rnglists)

* rnglists and loclists are handled differently (see:
  LoclistTableHeader, but no RnglistTableHeader)

* maybe all these types could be less stateful - lazily parse what they
  need to, even reparsing rather than caching because it doesn't seem
  too expensive, for instance. (though admittedly so long as it's
  constantcost/overead per compilatiton that's probably adequate)

* Maybe implementing and using a DWARFDataExtractor that can be
  sub-ranged (so we could slice it up to just the single contribution) -
  though maybe that's not so useful because loc/ranges need to refer to
  it by absolute, not contribution-relative mechanisms

Differential Revision: https://reviews.llvm.org/D86110
This commit is contained in:
David Blaikie 2020-08-14 07:56:29 -07:00
parent a3538b8394
commit f7a49d2aa6
8 changed files with 46 additions and 38 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.h
View File

@ -237,7 +237,9 @@ public:
llvm::Optional<uint64_t> GetRnglistOffset(uint32_t Index) const {
if (!m_rnglist_table)
return llvm::None;
if (llvm::Optional<uint64_t> off = m_rnglist_table->getOffsetEntry(Index))
if (llvm::Optional<uint64_t> off = m_rnglist_table->getOffsetEntry(
m_dwarf.GetDWARFContext().getOrLoadRngListsData().GetAsLLVM(),
Index))
return *off + m_ranges_base;
return llvm::None;
}
@ -246,7 +248,8 @@ public:
if (!m_loclist_table_header)
return llvm::None;
llvm::Optional<uint64_t> Offset = m_loclist_table_header->getOffsetEntry(Index);
llvm::Optional<uint64_t> Offset = m_loclist_table_header->getOffsetEntry(
m_dwarf.GetDWARFContext().getOrLoadLocListsData().GetAsLLVM(), Index);
if (!Offset)
return llvm::None;
return *Offset + m_loclists_base;

4
lldb/test/Shell/SymbolFile/DWARF/DW_AT_loclists_base.s
View File

@ -5,7 +5,7 @@
# CHECK-LABEL: image lookup -v -s lookup_loclists
# CHECK: Variable: {{.*}}, name = "x0", type = "int", location = DW_OP_reg0 RAX,
# CHECK: Variable: {{.*}}, name = "x1", type = "int", location = ,
# CHECK-NOT: Variable:
loclists:
nop
@ -28,7 +28,7 @@ lookup_loclists:
.short 5 # Version
.byte 8 # Address size
.byte 0 # Segment selector size
.long 1 # Offset entry count
.long 2 # Offset entry count
.Lloclists_table_base:
.long .Ldebug_loc0-.Lloclists_table_base
.long .Ldebug_loc1-.Lloclists_table_base

2
llvm/include/llvm/DebugInfo/DWARF/DWARFDebugLoc.h
View File

@ -72,6 +72,8 @@ public:
std::function<Optional<object::SectionedAddress>(uint32_t)> LookupAddr,
function_ref<bool(Expected<DWARFLocationExpression>)> Callback) const;
const DWARFDataExtractor &getData() { return Data; }
protected:
DWARFDataExtractor Data;

31
llvm/include/llvm/DebugInfo/DWARF/DWARFListTable.h
View File

@ -72,10 +72,6 @@ class DWARFListTableHeader {
};
Header HeaderData;
/// The offset table, which contains offsets to the individual list entries.
/// It is used by forms such as DW_FORM_rnglistx.
/// FIXME: Generate the table and use the appropriate forms.
std::vector<uint64_t> Offsets;
/// The table's format, either DWARF32 or DWARF64.
dwarf::DwarfFormat Format;
/// The offset at which the header (and hence the table) is located within
@ -93,7 +89,6 @@ public:
void clear() {
HeaderData = {};
Offsets.clear();
}
uint64_t getHeaderOffset() const { return HeaderOffset; }
uint8_t getAddrSize() const { return HeaderData.AddrSize; }
@ -115,11 +110,17 @@ public:
llvm_unreachable("Invalid DWARF format (expected DWARF32 or DWARF64");
}
void dump(raw_ostream &OS, DIDumpOptions DumpOpts = {}) const;
Optional<uint64_t> getOffsetEntry(uint32_t Index) const {
if (Index < Offsets.size())
return Offsets[Index];
return None;
void dump(DataExtractor Data, raw_ostream &OS,
DIDumpOptions DumpOpts = {}) const;
Optional<uint64_t> getOffsetEntry(DataExtractor Data, uint32_t Index) const {
if (Index > HeaderData.OffsetEntryCount)
return None;
uint8_t OffsetByteSize = Format == dwarf::DWARF64 ? 8 : 4;
uint64_t Offset =
getHeaderOffset() + getHeaderSize(Format) + OffsetByteSize * Index;
auto R = Data.getUnsigned(&Offset, OffsetByteSize);
return R;
}
/// Extract the table header and the array of offsets.
@ -169,14 +170,14 @@ public:
uint8_t getAddrSize() const { return Header.getAddrSize(); }
dwarf::DwarfFormat getFormat() const { return Header.getFormat(); }
void dump(raw_ostream &OS,
void dump(DWARFDataExtractor Data, raw_ostream &OS,
llvm::function_ref<Optional<object::SectionedAddress>(uint32_t)>
LookupPooledAddress,
DIDumpOptions DumpOpts = {}) const;
/// Return the contents of the offset entry designated by a given index.
Optional<uint64_t> getOffsetEntry(uint32_t Index) const {
return Header.getOffsetEntry(Index);
Optional<uint64_t> getOffsetEntry(DataExtractor Data, uint32_t Index) const {
return Header.getOffsetEntry(Data, Index);
}
/// Return the size of the table header including the length but not including
/// the offsets. This is dependent on the table format, which is unambiguously
@ -240,11 +241,11 @@ Error DWARFListType<ListEntryType>::extract(DWARFDataExtractor Data,
template <typename DWARFListType>
void DWARFListTableBase<DWARFListType>::dump(
raw_ostream &OS,
DWARFDataExtractor Data, raw_ostream &OS,
llvm::function_ref<Optional<object::SectionedAddress>(uint32_t)>
LookupPooledAddress,
DIDumpOptions DumpOpts) const {
Header.dump(OS, DumpOpts);
Header.dump(Data, OS, DumpOpts);
OS << HeaderString << "\n";
// Determine the length of the longest encoding string we have in the table,

11
llvm/include/llvm/DebugInfo/DWARF/DWARFUnit.h
View File

@ -412,18 +412,13 @@ public:
/// Return a rangelist's offset based on an index. The index designates
/// an entry in the rangelist table's offset array and is supplied by
/// DW_FORM_rnglistx.
Optional<uint64_t> getRnglistOffset(uint32_t Index) {
if (!RngListTable)
return None;
if (Optional<uint64_t> Off = RngListTable->getOffsetEntry(Index))
return *Off + RangeSectionBase;
return None;
}
Optional<uint64_t> getRnglistOffset(uint32_t Index);
Optional<uint64_t> getLoclistOffset(uint32_t Index) {
if (!LoclistTableHeader)
return None;
if (Optional<uint64_t> Off = LoclistTableHeader->getOffsetEntry(Index))
if (Optional<uint64_t> Off =
LoclistTableHeader->getOffsetEntry(LocTable->getData(), Index))
return *Off + getLocSectionBase();
return None;
}

4
llvm/lib/DebugInfo/DWARF/DWARFContext.cpp
View File

@ -255,7 +255,7 @@ static void dumpRnglistsSection(
break;
Offset = TableOffset + Length;
} else {
Rnglists.dump(OS, LookupPooledAddress, DumpOpts);
Rnglists.dump(rnglistData, OS, LookupPooledAddress, DumpOpts);
}
}
}
@ -316,7 +316,7 @@ static void dumpLoclistsSection(raw_ostream &OS, DIDumpOptions DumpOpts,
return;
}
Header.dump(OS, DumpOpts);
Header.dump(Data, OS, DumpOpts);
uint64_t EndOffset = Header.length() + Header.getHeaderOffset();
Data.setAddressSize(Header.getAddrSize());

9
llvm/lib/DebugInfo/DWARF/DWARFListTable.cpp
View File

@ -71,12 +71,12 @@ Error DWARFListTableHeader::extract(DWARFDataExtractor Data,
") than there is space for",
SectionName.data(), HeaderOffset, HeaderData.OffsetEntryCount);
Data.setAddressSize(HeaderData.AddrSize);
for (uint32_t I = 0; I < HeaderData.OffsetEntryCount; ++I)
Offsets.push_back(Data.getRelocatedValue(OffsetByteSize, OffsetPtr));
*OffsetPtr += HeaderData.OffsetEntryCount * OffsetByteSize;
return Error::success();
}
void DWARFListTableHeader::dump(raw_ostream &OS, DIDumpOptions DumpOpts) const {
void DWARFListTableHeader::dump(DataExtractor Data, raw_ostream &OS,
DIDumpOptions DumpOpts) const {
if (DumpOpts.Verbose)
OS << format("0x%8.8" PRIx64 ": ", HeaderOffset);
int OffsetDumpWidth = 2 * dwarf::getDwarfOffsetByteSize(Format);
@ -91,7 +91,8 @@ void DWARFListTableHeader::dump(raw_ostream &OS, DIDumpOptions DumpOpts) const {
if (HeaderData.OffsetEntryCount > 0) {
OS << "offsets: [";
for (const auto &Off : Offsets) {
for (uint32_t I = 0; I < HeaderData.OffsetEntryCount; ++I) {
auto Off = *getOffsetEntry(Data, I);
OS << format("\n0x%0*" PRIx64, OffsetDumpWidth, Off);
if (DumpOpts.Verbose)
OS << format(" => 0x%08" PRIx64,

16
llvm/lib/DebugInfo/DWARF/DWARFUnit.cpp
View File

@ -548,17 +548,13 @@ Error DWARFUnit::tryExtractDIEsIfNeeded(bool CUDieOnly) {
uint64_t HeaderSize = DWARFListTableHeader::getHeaderSize(Header.getFormat());
uint64_t Offset = getLocSectionBase();
DWARFDataExtractor Data(Context.getDWARFObj(), *LocSection,
isLittleEndian, getAddressByteSize());
const DWARFDataExtractor &Data = LocTable->getData();
if (Offset < HeaderSize)
return createStringError(errc::invalid_argument,
"did not detect a valid"
" list table with base = 0x%" PRIx64 "\n",
Offset);
Offset -= HeaderSize;
if (auto *IndexEntry = Header.getIndexEntry())
if (const auto *Contrib = IndexEntry->getContribution(DW_SECT_LOCLISTS))
Offset += Contrib->Offset;
if (Error E = LoclistTableHeader->extract(Data, &Offset))
return createStringError(errc::invalid_argument,
"parsing a loclist table: " +
@ -1009,3 +1005,13 @@ DWARFUnit::determineStringOffsetsTableContributionDWO(DWARFDataExtractor & DA) {
return DescOrError.takeError();
return *DescOrError;
}
Optional<uint64_t> DWARFUnit::getRnglistOffset(uint32_t Index) {
if (!RngListTable)
return None;
DataExtractor RangesData(RangeSection->Data, isLittleEndian,
getAddressByteSize());
if (Optional<uint64_t> Off = RngListTable->getOffsetEntry(RangesData, Index))
return *Off + RangeSectionBase;
return None;
}