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[lldb/DWARF] Don't get confused by line sequences with tombstone values
Summary: With D81784, lld has started debug info resolving relocations to garbage-collected symbols as -1 (instead of relocation addend). For an unaware consumer this generated sequences which seemingly wrap the address space -- their first entry was 0xfffff, but all other entries were low numbers. Lldb stores line sequences concatenated into one large vector, sorted by the first entry, and searched with std::lower_bound. This resulted in the low-value entries being placed at the end of the vector, which utterly confused the lower_bound algorithm, and caused it to not find a match. (Previously, these sequences would be at the start of the vector, and normally would contain addresses that are far smaller than any real address we want to look up, so std::lower_bound was fine.) This patch makes lldb ignore these kinds of sequences completely. It does that by changing the construction algorithm from iterating over the rows (as parsed by llvm), to iterating over the sequences. This is important because the llvm parsed performs validity checks when constructing the sequence array, whereas the row array contains raw data. Reviewers: JDevlieghere, MaskRay Differential Revision: https://reviews.llvm.org/D83957
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2 files changed

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‎lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

Lines changed: 12 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -1036,18 +1036,20 @@ bool SymbolFileDWARF::ParseLineTable(CompileUnit &comp_unit) {
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// FIXME: Rather than parsing the whole line table and then copying it over
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// into LLDB, we should explore using a callback to populate the line table
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// while we parse to reduce memory usage.
1039-
std::unique_ptr<LineSequence> sequence =
1040-
LineTable::CreateLineSequenceContainer();
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std::vector<std::unique_ptr<LineSequence>> sequences;
1042-
for (auto &row : line_table->Rows) {
1043-
LineTable::AppendLineEntryToSequence(
1044-
sequence.get(), row.Address.Address, row.Line, row.Column, row.File,
1045-
row.IsStmt, row.BasicBlock, row.PrologueEnd, row.EpilogueBegin,
1046-
row.EndSequence);
1047-
if (row.EndSequence) {
1048-
sequences.push_back(std::move(sequence));
1049-
sequence = LineTable::CreateLineSequenceContainer();
1040+
// The Sequences view contains only valid line sequences. Don't iterate over
1041+
// the Rows directly.
1042+
for (const llvm::DWARFDebugLine::Sequence &seq : line_table->Sequences) {
1043+
std::unique_ptr<LineSequence> sequence =
1044+
LineTable::CreateLineSequenceContainer();
1045+
for (unsigned idx = seq.FirstRowIndex; idx < seq.LastRowIndex; ++idx) {
1046+
const llvm::DWARFDebugLine::Row &row = line_table->Rows[idx];
1047+
LineTable::AppendLineEntryToSequence(
1048+
sequence.get(), row.Address.Address, row.Line, row.Column, row.File,
1049+
row.IsStmt, row.BasicBlock, row.PrologueEnd, row.EpilogueBegin,
1050+
row.EndSequence);
10501051
}
1052+
sequences.push_back(std::move(sequence));
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}
10521054

10531055
std::unique_ptr<LineTable> line_table_up =

‎lldb/test/Shell/SymbolFile/DWARF/debug_line-tombstone.s

Lines changed: 106 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,106 @@
1+
# This test that we don't get confused by line tables containing a tombstone
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# (-1) value, as produced by recent lld's. Line sequences with the tombstone
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# value should be completely ignored. The tombstone sequence is deliberately
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# longer so that any attempt at an address binary search will likely land inside
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# the sequence.
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# RUN: llvm-mc --filetype=obj --triple=x86_64-pc-linux %s -o %t
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# RUN: %lldb -o "image lookup -n main -v" -o "image dump line-table main.cpp" \
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# RUN: -o exit %t | FileCheck %s
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# CHECK-LABEL: image lookup -n main -v
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# CHECK: LineEntry: [0x0000000000001000-0x0000000000001001): main.cpp:1
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# CHECK-LABEL: image dump line-table main.cpp
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# CHECK-NEXT: Line table for main.cpp
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# CHECK-NEXT: 0x0000000000001000: main.cpp:1
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# CHECK-NEXT: 0x0000000000001001: main.cpp:1
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# CHECK-EMPTY:
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# CHECK-NEXT: exit
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.text
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.space 0x1000
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main:
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nop
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.Lmain_end:
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.section .debug_abbrev,"",@progbits
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.byte 1 # Abbreviation Code
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.byte 17 # DW_TAG_compile_unit
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.byte 0 # DW_CHILDREN_no
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.byte 37 # DW_AT_producer
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.byte 8 # DW_FORM_string
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.byte 3 # DW_AT_name
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.byte 8 # DW_FORM_string
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.byte 16 # DW_AT_stmt_list
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.byte 23 # DW_FORM_sec_offset
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.byte 17 # DW_AT_low_pc
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.byte 1 # DW_FORM_addr
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.byte 18 # DW_AT_high_pc
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.byte 6 # DW_FORM_data4
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.byte 0 # EOM(1)
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.byte 0 # EOM(2)
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.byte 0 # EOM(3)
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.section .debug_info,"",@progbits
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.Lcu_begin0:
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.long .Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
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.Ldebug_info_start0:
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.short 4 # DWARF version number
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.long 0 # Offset Into Abbrev. Section
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.byte 8 # Address Size (in bytes)
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.byte 1 # Abbrev [1] 0xb:0xc4 DW_TAG_compile_unit
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.asciz "Hand-written DWARF" # DW_AT_producer
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.asciz "main.cpp" # DW_AT_name
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.long 0 # DW_AT_stmt_list
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.quad main-.text # DW_AT_low_pc
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.long .Lmain_end-main # DW_AT_high_pc
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.Ldebug_info_end0:
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.section .debug_line,"",@progbits
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.long .Llt1_end - .Llt1_start # Length of Unit (DWARF-32 format)
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.Llt1_start:
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.short 4 # DWARF version number
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.long .Lprologue1_end-.Lprologue1_start # Length of Prologue
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.Lprologue1_start:
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.byte 1 # Minimum Instruction Length
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.byte 1 # Maximum Operations per Instruction
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.byte 1 # Default is_stmt
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.byte -5 # Line Base
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.byte 14 # Line Range
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.byte 13 # Opcode Base
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.byte 0, 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1 # Standard Opcode Lengths
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.byte 0
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.asciz "main.cpp" # File table
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.byte 0, 0, 0
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.byte 0
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.Lprologue1_end:
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.byte 0, 9, 2 # DW_LNE_set_address
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.quad -1
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.byte 1 # DW_LNS_copy
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 33 # address += 1, line += 1
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.byte 2 # DW_LNS_advance_pc
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.uleb128 1
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.byte 0, 1, 1 # DW_LNE_end_sequence
98+
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.byte 0, 9, 2 # DW_LNE_set_address
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.quad main-.text
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.byte 18 # address += 0, line += 0
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.byte 2 # DW_LNS_advance_pc
103+
.uleb128 1
104+
.byte 0, 1, 1 # DW_LNE_end_sequence
105+
.Llt1_end:
106+

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