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dwarfdump --statistics: Use new location list api

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Summary:
This patch removes manual location list handling in the statistics code
and replaces it with the new DWARFDie api, which provides access to a
"cooked" location list. This has the following effects:
- the code now properly handles split-dwarf location lists
- it will automatically support dwarf5 location lists once support for
  those is added
- it properly handles location lists with base address selection entries
- it fixes a bug where the location list code was using the first
  DW_AT_ranges range as a "base address" of the compile unit (it should
  have used DW_AT_low_pc instead. The effect of this was that the
  computation of the start address of a variable in its scope was broken
  for these kinds of compile units. This only manifested itself on
  linked files, since in object files the first DW_AT_ranges range
  normally starts at 0.

Since pretty much every kind of location list was broken in some way,
it's hard to verify that the new implementation is correct -- the output
will be different in all non-trivial cases, and mostly with good reason.

Most of the existing statistics tests continue to pass though, and a
visual inspection of the statistics for non-trivial inputs shows that
the data is more "reasonable" now. I have updated the "dwo statistics"
test to include the new numbers, as the previous ones were completely
bogus, and I have added a targeted test for the "base address" bug.

Reviewers: dblaikie, cmtice, vsk

Subscribers: aprantl, SouraVX, JDevlieghere, djtodoro, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70444
This commit is contained in:
Pavel Labath 2019-11-19 15:14:59 +01:00
parent 22c21b278b
commit 290efde9ec
3 changed files with 147 additions and 40 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

113
test/tools/llvm-dwarfdump/X86/statistics-base-address.s Normal file
View File

@ -0,0 +1,113 @@
# This tests the computation of the scope bytes covered by local variables. In
# particular, the case when the variable starts in the middle of the enclosing
# scope, and the compile unit has both DW_AT_ranges and DW_AT_low_pc attributes.
# RUN: llvm-mc -triple x86_64-pc-linux %s -filetype=obj -o %t
# RUN: llvm-dwarfdump --statistics %t | FileCheck %s
# CHECK: "vars scope bytes total":8
# CHECK: "vars scope bytes covered":8
.text
# Add padding to ensure the function does not start at address zero.
.zero 256
f: # @f
.Lf_begin:
.zero 4
.Lx_begin:
.zero 8
.Lf_end:
.section .debug_ranges,"",@progbits
.Ldebug_ranges:
.quad .Lf_begin
.quad .Lf_end
.quad 0
.quad 0
.section .debug_loc,"",@progbits
.Ldebug_loc:
.quad .Lx_begin
.quad .Lf_end
.short 1 # Loc expr size
.byte 85 # super-register DW_OP_reg5
.quad 0
.quad 0
.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 8 # DW_FORM_string
.byte 17 # DW_AT_low_pc
.byte 1 # DW_FORM_addr
.byte 85 # DW_AT_ranges
.byte 23 # DW_FORM_sec_offset
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 2 # Abbreviation Code
.byte 46 # DW_TAG_subprogram
.byte 1 # DW_CHILDREN_yes
.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 8 # DW_FORM_string
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 3 # Abbreviation Code
.byte 52 # DW_TAG_variable
.byte 0 # DW_CHILDREN_no
.byte 2 # DW_AT_location
.byte 23 # DW_FORM_sec_offset
.byte 3 # DW_AT_name
.byte 8 # DW_FORM_string
.byte 73 # DW_AT_type
.byte 19 # DW_FORM_ref4
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 5 # Abbreviation Code
.byte 36 # DW_TAG_base_type
.byte 0 # DW_CHILDREN_no
.byte 3 # DW_AT_name
.byte 8 # DW_FORM_string
.byte 62 # DW_AT_encoding
.byte 11 # DW_FORM_data1
.byte 11 # DW_AT_byte_size
.byte 11 # DW_FORM_data1
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 0 # EOM(3)
.section .debug_info,"",@progbits
.Lcu_begin:
.long .Ldebug_info_end-.Ldebug_info_start # Length of Unit
.Ldebug_info_start:
.short 4 # DWARF version number
.long .debug_abbrev # Offset Into Abbrev. Section
.byte 8 # Address Size (in bytes)
.byte 1 # Abbrev [1] 0xb:0x64 DW_TAG_compile_unit
.asciz "Hand-written DWARF" # DW_AT_producer
.quad 0 # DW_AT_low_pc
.long .Ldebug_ranges # DW_AT_ranges
.byte 2 # Abbrev [2] 0x2a:0x28 DW_TAG_subprogram
.quad .Lf_begin # DW_AT_low_pc
.long .Lf_end-.Lf_begin # DW_AT_high_pc
.asciz "f" # DW_AT_name
.byte 3 # Abbrev [3] 0x43:0xe DW_TAG_variable
.long .Ldebug_loc # DW_AT_location
.asciz "x" # DW_AT_name
.long .Lint # DW_AT_type
.byte 0 # End Of Children Mark
.Lint:
.byte 5 # Abbrev [5] 0x67:0x7 DW_TAG_base_type
.asciz "int" # DW_AT_name
.byte 5 # DW_AT_encoding
.byte 4 # DW_AT_byte_size
.byte 0 # End Of Children Mark
.Ldebug_info_end:

4
test/tools/llvm-dwarfdump/X86/statistics-dwo.test
View File

@ -80,8 +80,8 @@ CHECK: "source variables":30
# Ideally the value below would be 33 but currently it's not.
CHECK: "variables with location":22
CHECK: "call site entries":7
CHECK: "scope bytes total":2817
CHECK: "scope bytes covered":506
CHECK: "scope bytes total":2702
CHECK: "scope bytes covered":1160
CHECK: "total function size":594
CHECK: "total inlined function size":345
CHECK: "total formal params":12

70
tools/llvm-dwarfdump/Statistics.cpp
View File

@ -176,7 +176,7 @@ static void collectLocStats(uint64_t BytesCovered, uint64_t BytesInScope,
}
/// Collect debug info quality metrics for one DIE.
static void collectStatsForDie(DWARFDie Die, uint64_t UnitLowPC, std::string FnPrefix,
static void collectStatsForDie(DWARFDie Die, std::string FnPrefix,
std::string VarPrefix, uint64_t ScopeLowPC,
uint64_t BytesInScope, uint32_t InlineDepth,
StringMap<PerFunctionStats> &FnStatMap,
@ -243,41 +243,35 @@ static void collectStatsForDie(DWARFDie Die, uint64_t UnitLowPC, std::string FnP
return;
}
// Handle variables and function arguments.
auto FormValue = Die.find(dwarf::DW_AT_location);
HasLoc = FormValue.hasValue();
if (HasLoc) {
Expected<std::vector<DWARFLocationExpression>> Loc =
Die.getLocations(dwarf::DW_AT_location);
if (!Loc) {
consumeError(Loc.takeError());
} else {
HasLoc = true;
// Get PC coverage.
if (auto DebugLocOffset = FormValue->getAsSectionOffset()) {
auto *DebugLoc = Die.getDwarfUnit()->getContext().getDebugLoc();
// TODO: This code does not handle DWARF5 nor DWARF4 base address
// selection entries. This should use a higher-level API which abstracts
// these away.
if (auto List = DebugLoc->getLocationListAtOffset(*DebugLocOffset)) {
ArrayRef<DWARFLocationEntry> Entries = List->Entries;
// Ignore end-of-list entries
Entries = Entries.drop_back();
for (auto Entry : Entries) {
uint64_t BytesEntryCovered = Entry.Value1 - Entry.Value0;
BytesCovered += BytesEntryCovered;
if (IsEntryValue(Entry.Loc))
BytesEntryValuesCovered += BytesEntryCovered;
}
if (Entries.size()) {
uint64_t FirstDef = Entries[0].Value0;
uint64_t UnitOfs = UnitLowPC;
// Ranges sometimes start before the lexical scope.
if (UnitOfs + FirstDef >= ScopeLowPC)
OffsetToFirstDefinition = UnitOfs + FirstDef - ScopeLowPC;
// Or even after it. Count that as a failure.
if (OffsetToFirstDefinition > BytesInScope)
OffsetToFirstDefinition = 0;
}
}
assert(BytesInScope);
} else {
auto Default = find_if(
*Loc, [](const DWARFLocationExpression &L) { return !L.Range; });
if (Default != Loc->end()) {
// Assume the entire range is covered by a single location.
BytesCovered = BytesInScope;
} else {
for (auto Entry : *Loc) {
uint64_t BytesEntryCovered = Entry.Range->HighPC - Entry.Range->LowPC;
BytesCovered += BytesEntryCovered;
if (IsEntryValue(Entry.Expr))
BytesEntryValuesCovered += BytesEntryCovered;
}
if (!Loc->empty()) {
uint64_t FirstDef = Loc->front().Range->LowPC;
// Ranges sometimes start before the lexical scope.
if (FirstDef >= ScopeLowPC)
OffsetToFirstDefinition = FirstDef - ScopeLowPC;
// Or even after it. Count that as a failure.
if (OffsetToFirstDefinition > BytesInScope)
OffsetToFirstDefinition = 0;
}
assert(BytesInScope);
}
}
}
@ -356,7 +350,7 @@ static void collectStatsForDie(DWARFDie Die, uint64_t UnitLowPC, std::string FnP
}
/// Recursively collect debug info quality metrics.
static void collectStatsRecursive(DWARFDie Die, uint64_t UnitLowPC, std::string FnPrefix,
static void collectStatsRecursive(DWARFDie Die, std::string FnPrefix,
std::string VarPrefix, uint64_t ScopeLowPC,
uint64_t BytesInScope, uint32_t InlineDepth,
StringMap<PerFunctionStats> &FnStatMap,
@ -429,7 +423,7 @@ static void collectStatsRecursive(DWARFDie Die, uint64_t UnitLowPC, std::string
}
} else {
// Not a scope, visit the Die itself. It could be a variable.
collectStatsForDie(Die, UnitLowPC, FnPrefix, VarPrefix, ScopeLowPC, BytesInScope,
collectStatsForDie(Die, FnPrefix, VarPrefix, ScopeLowPC, BytesInScope,
InlineDepth, FnStatMap, GlobalStats, LocStats);
}
@ -447,7 +441,7 @@ static void collectStatsRecursive(DWARFDie Die, uint64_t UnitLowPC, std::string
if (Child.getTag() == dwarf::DW_TAG_lexical_block)
ChildVarPrefix += toHex(LexicalBlockIndex++) + '.';
collectStatsRecursive(Child, UnitLowPC, FnPrefix, ChildVarPrefix, ScopeLowPC,
collectStatsRecursive(Child, FnPrefix, ChildVarPrefix, ScopeLowPC,
BytesInScope, InlineDepth, FnStatMap, GlobalStats,
LocStats);
Child = Child.getSibling();
@ -502,8 +496,8 @@ bool collectStatsForObjectFile(ObjectFile &Obj, DWARFContext &DICtx,
StringMap<PerFunctionStats> Statistics;
for (const auto &CU : static_cast<DWARFContext *>(&DICtx)->compile_units())
if (DWARFDie CUDie = CU->getNonSkeletonUnitDIE(false))
collectStatsRecursive(CUDie, getLowPC(CUDie), "/", "g", 0, 0, 0,
Statistics, GlobalStats, LocStats);
collectStatsRecursive(CUDie, "/", "g", 0, 0, 0, Statistics, GlobalStats,
LocStats);
/// The version number should be increased every time the algorithm is changed
/// (including bug fixes). New metrics may be added without increasing the