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[lldb/DWARF] Don't treat class declarations with children as definitions 

Summary:
This effectively reverts r188124, which added code to handle
(DW_AT_)declarations of structures with some kinds of children as
definitions. The commit message claims this is a workaround for some
kind of debug info produced by gcc. However, it does not go into
specifics, so it's hard to reproduce or verify that this is indeed still a
problem.

Having this code is definitely a problem though, because it mistakenly
declares incomplete dwarf declarations to be complete. Both clang (with
-flimit-debug-info) and gcc (by default) generate DW_AT_declarations of
structs with children. This happens when full debug info for a class is
not emitted in a given compile unit (e.g. because of vtable homing), but
the class has inline methods which are used in the given compile unit.
In that case, the compilers emit a DW_AT_declaration of a class, but
add a DW_TAG_subprogram child to it to describe the inlined instance of
the method.

Even though the class tag has some children, it definitely does not
contain enough information to construct a full class definition (most
notably, it lacks any members). Keeping the class as incomplete allows
us to search for a real definition in other modules, helping the
-flimit-debug-info flow. And in case the definition is not found we can
display a error message saying that, instead of just showing an empty
struct.

Reviewers: clayborg, aprantl, JDevlieghere, shafik

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D83302
This commit is contained in:
Pavel Labath 2020-07-07 15:28:24 +02:00
parent 6701c0bf73
commit 1956cf1042
7 changed files with 208 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
lldb/source/Plugins/SymbolFile/DWARF/DWARFASTParserClang.cpp
View File

@ -1641,33 +1641,6 @@ DWARFASTParserClang::ParseStructureLikeDIE(const SymbolContext &sc,
dwarf->GetUniqueDWARFASTTypeMap().Insert(unique_typename,
*unique_ast_entry_up);
if (attrs.is_forward_declaration && die.HasChildren()) {
// Check to see if the DIE actually has a definition, some version of
// GCC will
// emit DIEs with DW_AT_declaration set to true, but yet still have
// subprogram, members, or inheritance, so we can't trust it
DWARFDIE child_die = die.GetFirstChild();
while (child_die) {
switch (child_die.Tag()) {
case DW_TAG_inheritance:
case DW_TAG_subprogram:
case DW_TAG_member:
case DW_TAG_APPLE_property:
case DW_TAG_class_type:
case DW_TAG_structure_type:
case DW_TAG_enumeration_type:
case DW_TAG_typedef:
case DW_TAG_union_type:
child_die.Clear();
attrs.is_forward_declaration = false;
break;
default:
child_die = child_die.GetSibling();
break;
}
}
}
if (!attrs.is_forward_declaration) {
// Always start the definition for a class type so that if the class
// has child classes or types that require the class to be created

25
lldb/test/API/functionalities/limit-debug-info/TestLimitDebugInfo.py
View File

@ -38,7 +38,8 @@ class LimitDebugInfoTestCase(TestBase):
self._check_debug_info_is_limited(target)
self.registerSharedLibrariesWithTarget(target, ["one", "two"])
lldbutil.run_to_name_breakpoint(self, "main",
extra_images=["one", "two"])
# But when other shared libraries are loaded, we should be able to see
# all members.
@ -58,6 +59,10 @@ class LimitDebugInfoTestCase(TestBase):
self.expect_expr("array_of_two[2].one[2].member", result_value="174")
self.expect_expr("array_of_two[2].member", result_value="274")
self.expect_expr("get_one().member", result_value="124")
self.expect_expr("get_two().one().member", result_value="124")
self.expect_expr("get_two().member", result_value="224")
@skipIf(bugnumber="pr46284", debug_info="gmodules")
@skipIfWindows # Clang emits type info even with -flimit-debug-info
def test_two_debug(self):
@ -66,7 +71,8 @@ class LimitDebugInfoTestCase(TestBase):
self._check_debug_info_is_limited(target)
self.registerSharedLibrariesWithTarget(target, ["one", "two"])
lldbutil.run_to_name_breakpoint(self, "main",
extra_images=["one", "two"])
# This time, we should only see the members from the second library.
self.expect_expr("inherits_from_one.member", result_value="47")
@ -91,6 +97,12 @@ class LimitDebugInfoTestCase(TestBase):
substrs=["no member named 'member' in 'array::One'"])
self.expect_expr("array_of_two[2].member", result_value="274")
self.expect("expr get_one().member", error=True,
substrs=["calling 'get_one' with incomplete return type 'result::One'"])
self.expect("expr get_two().one().member", error=True,
substrs=["calling 'one' with incomplete return type 'result::One'"])
self.expect_expr("get_two().member", result_value="224")
@skipIf(bugnumber="pr46284", debug_info="gmodules")
@skipIfWindows # Clang emits type info even with -flimit-debug-info
def test_one_debug(self):
@ -99,7 +111,8 @@ class LimitDebugInfoTestCase(TestBase):
self._check_debug_info_is_limited(target)
self.registerSharedLibrariesWithTarget(target, ["one", "two"])
lldbutil.run_to_name_breakpoint(self, "main",
extra_images=["one", "two"])
# In this case we should only see the members from the second library.
# Note that we cannot see inherits_from_two.one because without debug
@ -126,3 +139,9 @@ class LimitDebugInfoTestCase(TestBase):
substrs=["no member named 'one' in 'array::Two'"])
self.expect("expr array_of_two[2].member", error=True,
substrs=["no member named 'member' in 'array::Two'"])
self.expect_expr("get_one().member", result_value="124")
self.expect("expr get_two().one().member", error=True,
substrs=["calling 'get_two' with incomplete return type 'result::Two'"])
self.expect("expr get_two().member", error=True,
substrs=["calling 'get_two' with incomplete return type 'result::Two'"])

5
lldb/test/API/functionalities/limit-debug-info/main.cpp
View File

@ -25,4 +25,7 @@ struct TwoAsMember {
array::One array_of_one[3];
array::Two array_of_two[3];
int main() { return 0; }
result::One get_one() { return result::One(124); }
result::Two get_two() { return result::Two(224); }
int main() { return get_one().member; }

3
lldb/test/API/functionalities/limit-debug-info/one.cpp
View File

@ -3,3 +3,6 @@
One::~One() = default;
member::One::~One() = default;
array::One::~One() = default;
result::One::One(int member) : member(member) {}
result::One::~One() = default;

15
lldb/test/API/functionalities/limit-debug-info/onetwo.h
View File

@ -39,3 +39,18 @@ struct Two {
virtual ~Two();
};
} // namespace array
namespace result {
struct One {
int member;
One(int member);
virtual ~One();
};
struct Two {
int member;
Two(int member);
One one() const;
virtual ~Two();
};
} // namespace result

4
lldb/test/API/functionalities/limit-debug-info/two.cpp
View File

@ -3,3 +3,7 @@
Two::~Two() = default;
member::Two::~Two() = default;
array::Two::~Two() = default;
result::Two::Two(int member) : member(member) {}
result::Two::~Two() = default;
result::One result::Two::one() const { return One(member - 100); }

160
lldb/test/Shell/SymbolFile/DWARF/DW_AT_declaration-with-children.s Normal file
View File

@ -0,0 +1,160 @@
# Test that a forward-declared (DW_AT_declaration) structure is treated as a
# forward-declaration even if it has children. These types can be produced due
# to vtable-based type homing, or other -flimit-debug-info optimizations.
# REQUIRES: x86
# RUN: llvm-mc --triple x86_64-pc-linux %s --filetype=obj > %t
# RUN: %lldb %t -o "expr a" -o exit 2>&1 | FileCheck %s --check-prefix=EXPR
# RUN: %lldb %t -o "target var a" -o exit 2>&1 | FileCheck %s --check-prefix=VAR
# EXPR: incomplete type 'A' where a complete type is required
# FIXME: This should also produce some kind of an error.
# VAR: (A) a = {}
.text
_ZN1AC2Ev:
retq
.LZN1AC2Ev_end:
.data
a:
.quad $_ZTV1A+16
.quad $0xdeadbeef
.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 18 # DW_AT_high_pc
.byte 6 # DW_FORM_data4
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 2 # Abbreviation Code
.byte 52 # DW_TAG_variable
.byte 0 # DW_CHILDREN_no
.byte 3 # DW_AT_name
.byte 8 # DW_FORM_string
.byte 73 # DW_AT_type
.byte 19 # DW_FORM_ref4
.byte 2 # DW_AT_location
.byte 24 # DW_FORM_exprloc
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 3 # Abbreviation Code
.byte 19 # DW_TAG_structure_type
.byte 1 # DW_CHILDREN_yes
.byte 3 # DW_AT_name
.byte 8 # DW_FORM_string
.byte 60 # DW_AT_declaration
.byte 25 # DW_FORM_flag_present
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 4 # Abbreviation Code
.byte 46 # DW_TAG_subprogram
.byte 1 # DW_CHILDREN_yes
.byte 3 # DW_AT_name
.byte 8 # DW_FORM_string
.byte 60 # DW_AT_declaration
.byte 25 # DW_FORM_flag_present
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 5 # Abbreviation Code
.byte 5 # DW_TAG_formal_parameter
.byte 0 # DW_CHILDREN_no
.byte 73 # DW_AT_type
.byte 19 # DW_FORM_ref4
.byte 52 # DW_AT_artificial
.byte 25 # DW_FORM_flag_present
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 8 # Abbreviation Code
.byte 15 # DW_TAG_pointer_type
.byte 0 # DW_CHILDREN_no
.byte 73 # DW_AT_type
.byte 19 # DW_FORM_ref4
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 10 # 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 64 # DW_AT_frame_base
.byte 24 # DW_FORM_exprloc
.byte 100 # DW_AT_object_pointer
.byte 19 # DW_FORM_ref4
.byte 71 # DW_AT_specification
.byte 19 # DW_FORM_ref4
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 11 # Abbreviation Code
.byte 5 # DW_TAG_formal_parameter
.byte 0 # DW_CHILDREN_no
.byte 2 # DW_AT_location
.byte 24 # DW_FORM_exprloc
.byte 3 # DW_AT_name
.byte 8 # DW_FORM_string
.byte 73 # DW_AT_type
.byte 19 # DW_FORM_ref4
.byte 52 # DW_AT_artificial
.byte 25 # DW_FORM_flag_present
.byte 0 # EOM(1)
.byte 0 # EOM(2)
.byte 0 # EOM(3)
.section .debug_info,"",@progbits
.Lcu_begin0:
.long .Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
.Ldebug_info_start0:
.short 4 # DWARF version number
.long .debug_abbrev # Offset Into Abbrev. Section
.byte 8 # Address Size (in bytes)
.byte 1 # Abbrev [1] DW_TAG_compile_unit
.asciz "Hand-written DWARF" # DW_AT_producer
.quad _ZN1AC2Ev # DW_AT_low_pc
.long .LZN1AC2Ev_end-_ZN1AC2Ev # DW_AT_high_pc
.byte 2 # Abbrev [2] DW_TAG_variable
.asciz "a" # DW_AT_name
.long .LA-.Lcu_begin0 # DW_AT_type
.byte 9 # DW_AT_location
.byte 3
.quad a
.LA:
.byte 3 # Abbrev [3] DW_TAG_structure_type
.asciz "A" # DW_AT_name
# DW_AT_declaration
.byte 4 # Abbrev [4] DW_TAG_subprogram
.asciz "A" # DW_AT_name
# DW_AT_declaration
.byte 5 # Abbrev [5] DW_TAG_formal_parameter
.long .LAptr-.Lcu_begin0 # DW_AT_type
# DW_AT_artificial
.byte 0 # End Of Children Mark
.byte 0 # End Of Children Mark
.LAptr:
.byte 8 # Abbrev [8] DW_TAG_pointer_type
.long .LA-.Lcu_begin0 # DW_AT_type
.byte 10 # Abbrev [10] DW_TAG_subprogram
.quad _ZN1AC2Ev # DW_AT_low_pc
.long .LZN1AC2Ev_end-_ZN1AC2Ev # DW_AT_high_pc
.byte 1 # DW_AT_frame_base
.byte 86
.long 147 # DW_AT_object_pointer
.long 68 # DW_AT_specification
.byte 11 # Abbrev [11] DW_TAG_formal_parameter
.byte 2 # DW_AT_location
.byte 145
.byte 120
.asciz "this" # DW_AT_name
.long .LAptr-.Lcu_begin0 # DW_AT_type
# DW_AT_artificial
.byte 0 # End Of Children Mark
.byte 0 # End Of Children Mark
.Ldebug_info_end0: