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DWARF: Don't create lldb CompileUnits for DWARF type units
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Summary:
Type units don't represent actual compilations and a lot of the
operations that we do with lldb compile units (getting their line
tables, variables, etc.) don't make sense for them. There is also a lot
more of them (sometimes over 100x), so making them more lightweight pays
off.

The main change in this patch is that we stop creating lldb CompileUnits
for DWARF type units. The trickiest part here is that the SymbolFile
interface requires that we assign consecutive sequence IDs to the
compile units we create. As DWARF type and compile units can come in any
order (in v5), this means we can no longer use 1-1 mapping between DWARF
and lldb compile units. Instead I build a translation table between the
two indices. To avoid pessimizing the case where there are no type
units, I build the translation table only in case we have at least one
type unit.

Additionaly, I also tried to strenghted type safete by replacing
DWARFUnit with DWARFCompileUnit where applicable. Though that was not
stricly necessary, I found it a good way to ensure that the
transformations I am doing here make sense. In the places where I was
changing the function signatures, and where it was obvious that the
objects being handled were not null, I also replaced pointers with
references.

There shouldn't be any major functional change with this patch. The only
change I observed is that now the types in the type units will not be
parsed when one calls Module::ParseAllDebugSymbols, unless they are
referenced from other compile units. This makes sense, given how
ParseAllDebugSymbols is implemented (it iterates over all compile
units), and it only matters for one hand-writted test where I did not
bother to reference the types from the compile units (which I now do).

Reviewers: clayborg, JDevlieghere, aprantl

Subscribers: jdoerfert, lldb-commits

Differential Revision: https://reviews.llvm.org/D63005

llvm-svn: 363250
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@labath
labath committed Jun 13, 2019
1 parent a6b87aa commit ad17e28
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Showing 13 changed files with 355 additions and 199 deletions.
94 changes: 94 additions & 0 deletions lldb/lit/SymbolFile/DWARF/debug-types-dwarf5.s
View file
@@ -0,0 +1,94 @@
# RUN: llvm-mc -triple=x86_64-pc-linux -filetype=obj %s > %t
# RUN: %lldb %t -o "image lookup -v -s f1" -o exit | FileCheck %s

# CHECK: Function: id = {0x7fffffff0000003c}, name = "f1", range = [0x0000000000000000-0x0000000000000001)
# CHECK: Blocks: id = {0x7fffffff0000003c}, range = [0x00000000-0x00000001)


.text
.globl f1
.type f1,@function
f1:
nop
.Lfunc_end0:
.size f1, .Lfunc_end0-f1
# -- End function
.section .debug_str,"MS",@progbits,1
.Lproducer:
.asciz "Hand-written DWARF"
.Lf1:
.asciz "f1"
.Le1:
.asciz "e1"

.section .debug_abbrev,"",@progbits
.byte 1 # Abbreviation Code
.byte 17 # DW_TAG_compile_unit
.byte 1 # DW_CHILDREN_yes
.byte 37 # DW_AT_producer
.byte 14 # DW_FORM_strp
.byte 17 # DW_AT_low_pc
.byte 1 # DW_FORM_addr
.byte 18 # DW_AT_high_pc
.byte 6 # DW_FORM_data4
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 2 # Abbreviation Code
.byte 46 # DW_TAG_subprogram
.byte 0 # DW_CHILDREN_no
.byte 17 # DW_AT_low_pc
.byte 1 # DW_FORM_addr
.byte 18 # DW_AT_high_pc
.byte 6 # DW_FORM_data4
.byte 3 # DW_AT_name
.byte 14 # DW_FORM_strp
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 3 # Abbreviation Code
.byte 65 # DW_TAG_type_unit
.byte 1 # DW_CHILDREN_yes
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 5 # Abbreviation Code
.byte 4 # DW_TAG_enumeration_type
.byte 0 # DW_CHILDREN_no
.byte 3 # DW_AT_name
.byte 14 # DW_FORM_strp
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 0 # EOM(3)

.section .debug_info,"",@progbits
.Ltu_begin0:
.long .Ltu_end0-.Ltu_start0 # Length of Unit
.Ltu_start0:
.short 5 # DWARF version number
.byte 2 # DWARF Unit Type
.byte 8 # Address Size (in bytes)
.long .debug_abbrev # Offset Into Abbrev. Section
.quad 47 # Type Signature
.long .Ltype-.Ltu_begin0 # Type DIE Offset
.byte 3 # Abbrev [1] 0x18:0x1d DW_TAG_type_unit
.Ltype:
.byte 5 # Abbrev [5] 0x2e:0x9 DW_TAG_enumeration_type
.long .Le1 # DW_AT_name
.byte 0 # End Of Children Mark
.Ltu_end0:

.Lcu_begin0:
.long .Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
.Ldebug_info_start0:
.short 5 # DWARF version number
.byte 1 # DWARF Unit Type
.byte 8 # Address Size (in bytes)
.long .debug_abbrev # Offset Into Abbrev. Section
.byte 1 # Abbrev [1] 0xc:0x5f DW_TAG_compile_unit
.long .Lproducer # DW_AT_producer
.quad f1 # DW_AT_low_pc
.long .Lfunc_end0-f1 # DW_AT_high_pc
.byte 2 # Abbrev [2] 0x2b:0x37 DW_TAG_subprogram
.quad f1 # DW_AT_low_pc
.long .Lfunc_end0-f1 # DW_AT_high_pc
.long .Lf1 # DW_AT_name
.byte 0 # End Of Children Mark
.Ldebug_info_end0:
17 changes: 17 additions & 0 deletions lldb/lit/SymbolFile/DWARF/debug-types-line-tables.s
View file
Expand Up @@ -169,6 +169,13 @@
.byte 1 # DW_CHILDREN_yes
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 5 # Abbreviation Code
.byte 19 # DW_TAG_structure_type
.byte 0 # DW_CHILDREN_no
.byte 105 # DW_AT_signature
.byte 32 # DW_FORM_ref_sig8
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 0 # EOM(3)
.section .debug_info,"",@progbits
.Lcu_begin0:
Expand All @@ -178,6 +185,16 @@
.long .debug_abbrev # Offset Into Abbrev. Section
.byte 8 # Address Size (in bytes)
.byte 4 # Abbrev [4] 0xb:0x32 DW_TAG_compile_unit
.byte 5 # Abbrev [5] DW_TAG_structure_type
.quad 5390450678491038984 # DW_AT_signature
.byte 5 # Abbrev [5] DW_TAG_structure_type
.quad 5390450678491038985 # DW_AT_signature
.byte 5 # Abbrev [5] DW_TAG_structure_type
.quad 5390450678491038986 # DW_AT_signature
.byte 5 # Abbrev [5] DW_TAG_structure_type
.quad 5390450678491038987 # DW_AT_signature
.byte 5 # Abbrev [5] DW_TAG_structure_type
.quad 5390450678491038988 # DW_AT_signature
.byte 0 # End Of Children Mark
.Ldebug_info_end1:

Expand Down
4 changes: 2 additions & 2 deletions lldb/source/Plugins/SymbolFile/DWARF/DWARFCompileUnit.cpp
View file
Expand Up @@ -70,7 +70,7 @@ void DWARFCompileUnit::BuildAddressRangeTable(
// We got nothing from the functions, maybe we have a line tables only
// situation. Check the line tables and build the arange table from this.
SymbolContext sc;
sc.comp_unit = m_dwarf->GetCompUnitForDWARFCompUnit(this);
sc.comp_unit = m_dwarf->GetCompUnitForDWARFCompUnit(*this);
if (sc.comp_unit) {
SymbolFileDWARFDebugMap *debug_map_sym_file =
m_dwarf->GetDebugMapSymfile();
Expand All @@ -96,7 +96,7 @@ void DWARFCompileUnit::BuildAddressRangeTable(
// We got nothing from the functions, maybe we have a line tables only
// situation. Check the line tables and build the arange table from this.
SymbolContext sc;
sc.comp_unit = m_dwarf->GetCompUnitForDWARFCompUnit(this);
sc.comp_unit = m_dwarf->GetCompUnitForDWARFCompUnit(*this);
if (sc.comp_unit) {
if (LineTable *line_table = sc.comp_unit->GetLineTable()) {
LineTable::FileAddressRanges file_ranges;
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5 changes: 5 additions & 0 deletions lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp
View file
Expand Up @@ -182,6 +182,11 @@ DWARFTypeUnit *DWARFDebugInfo::GetTypeUnitForHash(uint64_t hash) {
return llvm::cast<DWARFTypeUnit>(GetUnitAtIndex(pos->second));
}

bool DWARFDebugInfo::ContainsTypeUnits() {
ParseUnitHeadersIfNeeded();
return !m_type_hash_to_unit_index.empty();
}

DWARFDIE
DWARFDebugInfo::GetDIEForDIEOffset(DIERef::Section section,
dw_offset_t die_offset) {
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1 change: 1 addition & 0 deletions lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.h
View file
Expand Up @@ -48,6 +48,7 @@ class DWARFDebugInfo {
dw_offset_t die_offset);
DWARFUnit *GetUnit(const DIERef &die_ref);
DWARFTypeUnit *GetTypeUnitForHash(uint64_t hash);
bool ContainsTypeUnits();
DWARFDIE GetDIEForDIEOffset(DIERef::Section section,
dw_offset_t die_offset);
DWARFDIE GetDIE(const DIERef &die_ref);
Expand Down

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