当我尝试评估LLDB中的表达式（捆绑在Xcode 7.3中），其中C ++结构的整数字段除以另一个整数常量时，我发现LLDB似乎没有按预期进行评估：
(lldb) l 1
1 #include <cstdio>
2
3 typedef struct {
4 int value;
5 } Item;
6
7 int main() {
8
9 Item item;
10 item.value = 1800;
(lldb)
11 printf("%d\n", item.value);
12 return 0;
13 }
(lldb) b 11
Breakpoint 1: where = x`main + 29 at a.cpp:11, address = 0x0000000100000f6d
(lldb) run
Process 44385 launched: '/tmp/x' (x86_64)
Process 44385 stopped
* thread #1: tid = 0x53ad87, 0x0000000100000f6d x`main + 29 at a.cpp:11, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
frame #0: 0x0000000100000f6d x`main + 29 at a.cpp:11
8
9 Item item;
10 item.value = 1800;
-> 11 printf("%d\n", item.value);
12 return 0;
13 }
(lldb) p item.value
(int) $0 = 1800
(lldb) p item.value / 2
(int) $1 = 0
(lldb) p item.value / 2.0
(double) $2 = 900
请注意，item.value / 2被评估为0但item.value / 2.0 900。
这种行为是否适用于LLDB的设计？这是一个已知的错误吗？
修改
以下是启用日志表达式后的输出：
(lldb) p item.value/2
== [UserExpression::Evaluate] Parsing expression item.value/2 ==
ClangUserExpression::ScanContext()
Parsing the following code:
#ifndef NULL
#define NULL (__null)
#endif
#ifndef Nil
#define Nil (__null)
#endif
#ifndef nil
#define nil (__null)
#endif
#ifndef YES
#define YES ((BOOL)1)
#endif
#ifndef NO
#define NO ((BOOL)0)
#endif
typedef __INT8_TYPE__ int8_t;
typedef __UINT8_TYPE__ uint8_t;
typedef __INT16_TYPE__ int16_t;
typedef __UINT16_TYPE__ uint16_t;
typedef __INT32_TYPE__ int32_t;
typedef __UINT32_TYPE__ uint32_t;
typedef __INT64_TYPE__ int64_t;
typedef __UINT64_TYPE__ uint64_t;
typedef __INTPTR_TYPE__ intptr_t;
typedef __UINTPTR_TYPE__ uintptr_t;
typedef __SIZE_TYPE__ size_t;
typedef __PTRDIFF_TYPE__ ptrdiff_t;
typedef unsigned short unichar;
extern "C"
{
int printf(const char * __restrict, ...);
}
typedef signed char BOOL;
void
$__lldb_expr(void *$__lldb_arg)
{
item.value/2;
}
LayoutRecordType[1] on (ASTContext*)0x7fbedb9aba00 for (RecordDecl*)0x7fbedb9843b0 [name = '_objc_super']
LayoutRecordType[2] on (ASTContext*)0x7fbedb9aba00 for (RecordDecl*)0x7fbedb984680 [name = '_message_ref_t']
ClangExpressionDeclMap::FindExternalVisibleDecls[0] for '$__lldb_arg' in a 'TranslationUnit'
CEDM::FEVD[0] Searching the root namespace
ClangASTSource::FindExternalVisibleDecls[0] on (ASTContext*)0x7fbedb9aba00 for '$__lldb_arg' in a 'TranslationUnit'
CAS::FEVD[0] Searching the root namespace
ClangExpressionDeclMap::FindExternalVisibleDecls[1] for '$__lldb_expr' in a 'TranslationUnit'
CEDM::FEVD[1] Searching the root namespace
ClangASTSource::FindExternalVisibleDecls[1] on (ASTContext*)0x7fbedb9aba00 for '$__lldb_expr' in a 'TranslationUnit'
CAS::FEVD[1] Searching the root namespace
ClangExpressionDeclMap::FindExternalVisibleDecls[2] for 'item' in a 'TranslationUnit'
CEDM::FEVD[2] Searching the root namespace
[ClangASTImporter] Imported (CXXRecordDecl*)0x7fbedb22f128, named (from (Decl*)0x7fbedaa596d8), metadata 0x375
[ClangASTImporter] Decl has no origin information in (ASTContext*)0x7fbedaa50c00
[ClangASTImporter] To is a TagDecl - attributes Lexical [complete->incomplete]
[ClangASTImporter] Imported (TypedefDecl*)0x7fbedb22f260, named Item (from (Decl*)0x7fbedaa59810), metadata 0xffffffffffffffff
[ClangASTImporter] Decl has no origin information in (ASTContext*)0x7fbedaa50c00
CEDM::FEVD[2] Found variable item, returned static Item &item (original Item)
FindExternalLexicalDecls[0] on (ASTContext*)0x7fbedb9aba00 in '' (CXXRecordDecl*)0x7fbedb22f128
FELD[0] Original decl (ASTContext*)0x7fbedaa50c00 (Decl*)0x7fbedaa596d8:
struct {
int value;
}
FELD[0] Adding [to CXXRecordDecl ] lexical FieldDecl int value
[ClangASTImporter] Imported (FieldDecl*)0x7fbedb22f3c8, named value (from (Decl*)0x7fbedaa598e0), metadata 0x379
[ClangASTImporter] Decl has no origin information in (ASTContext*)0x7fbedaa50c00
Last statement is an rvalue with type: int
LayoutRecordType[3] on (ASTContext*)0x7fbedb9aba00 for (RecordDecl*)0x7fbedb22f128 [name = '']
LRT[3] returned:
LRT[3] Original = (RecordDecl*)0x7fbedaa596d8
LRT[3] Size = 32
LRT[3] Alignment = 32
LRT[3] Fields:
LRT[3] (FieldDecl*)0x7fbedb22f3c8, Name = 'value', Offset = 0 bits
LRT[3] Bases:
Found function _Z12$__lldb_exprPv for $__lldb_expr
Module as passed in to IRForTarget:
"; ModuleID = '$__lldb_module'
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx"
%struct.anon = type { i32 }
@"_ZZ12$__lldb_exprPvE19$__lldb_expr_result" = internal global i32 0, align 4
@"_ZGVZ12$__lldb_exprPvE19$__lldb_expr_result" = internal global i8 0, align 1
@_ZL4item = external constant %struct.anon*, align 8
; Function Attrs: nounwind
define void @"_Z12$__lldb_exprPv"(i8* %"$__lldb_arg") #0 {
%1 = alloca i8*, align 8, !clang.decl.ptr !8
store i8* %"$__lldb_arg", i8** %1, align 8
%2 = load i8, i8* @"_ZGVZ12$__lldb_exprPvE19$__lldb_expr_result", align 1
%3 = icmp eq i8 %2, 0
br i1 %3, label %4, label %9
; <label>:4 ; preds = %0
%5 = load %struct.anon*, %struct.anon** @_ZL4item, align 8
%6 = getelementptr inbounds %struct.anon, %struct.anon* %5, i32 0, i32 0
%7 = load i32, i32* %6, align 4
%8 = sdiv i32 %7, 2
store i32 %8, i32* @"_ZZ12$__lldb_exprPvE19$__lldb_expr_result", align 4
store i8 1, i8* @"_ZGVZ12$__lldb_exprPvE19$__lldb_expr_result", align 1
br label %9
; <label>:9 ; preds = %4, %0
ret void
}
attributes #0 = { nounwind "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="0" "target-features"="+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
!clang.global.decl.ptrs = !{!0, !1, !0, !2}
!llvm.module.flags = !{!3, !4, !5, !6}
!llvm.ident = !{!7}
!0 = !{i32* @"_ZZ12$__lldb_exprPvE19$__lldb_expr_result", i64 140457697014984}
!1 = !{void (i8*)* @"_Z12$__lldb_exprPv", i64 140457697013856}
!2 = !{%struct.anon** @_ZL4item, i64 140457697014568}
!3 = !{i32 1, !"Objective-C Version", i32 2}
!4 = !{i32 1, !"Objective-C Image Info Version", i32 0}
!5 = !{i32 1, !"Objective-C Image Info Section", !"__DATA, __objc_imageinfo, regular, no_dead_strip"}
!6 = !{i32 4, !"Objective-C Garbage Collection", i32 0}
!7 = !{!"Apple LLVM version 3.8.0 (clang-703.0.29)"}
!8 = !{i64 140457704716640}
"
Result name: "_ZZ12$__lldb_exprPvE19$__lldb_expr_result"
Found result in the IR: "@"_ZZ12$__lldb_exprPvE19$__lldb_expr_result" = internal global i32 0, align 4"
Found result decl: "static int $__lldb_expr_resultitem.value / 2"
Result decl type: "int"
Creating a new result global: "$RESULT_NAME" with size 0x4
Replacing "@"_ZZ12$__lldb_exprPvE19$__lldb_expr_result" = internal global i32 0, align 4" with "@"$RESULT_NAME" = external global i32"
[ClangASTImporter] DeportType called on (BuiltinType*)0x7fbedb983dc0 from (ASTContext*)0x7fbedb9aba00 to (ASTContext*)0x7fbedab3fa00
Examining non-declaration function _Z12$__lldb_exprPv
Examining _ZGVZ12$__lldb_exprPvE19$__lldb_expr_result, DeclForGlobalValue returns 0x0
Examining _ZL4item, DeclForGlobalValue returns 0x7fbedb22f328
MaybeHandleVariable (@_ZL4item = external constant %struct.anon*, align 8)
Type of "item" is [clang "Item &", llvm "%struct.anon**"] [size 8, align 8]
Adding value for (NamedDecl*)0x7fbedb22f328 [item - item] to the structure
Placed at 0x8
Examining reloc_placeholder, DeclForGlobalValue returns 0x0
Examining $RESULT_NAME, DeclForGlobalValue returns 0x7fbedb22f4c8
MaybeHandleVariable (@"$RESULT_NAME" = external global i32)
Type of "$__lldb_expr_result" is [clang "int *", llvm "i32**"] [size 8, align 8]
Adding value for (NamedDecl*)0x7fbedb22f4c8 [$__lldb_expr_result - $RESULT_NAME] to the structure
Already placed at 0x0
Placed at 0x0
Element arrangement:
Arg: "i8* %"$__lldb_arg""
"item" ("item") placed at 8
Replacing [@_ZL4item = external constant %struct.anon*, align 8]
"$RESULT_NAME" ("$__lldb_expr_result") placed at 0
Replacing [@"$RESULT_NAME" = external global i32]
Total structure [align 8, size 16]
Did remove @"_ZGVZ12$__lldb_exprPvE19$__lldb_expr_result" = internal global i8 0, align 1
Did remove @reloc_placeholder = internal global i8 0
== ClangASTMetrics output ==
-- Global metrics --
Number of visible Decl queries by name : 5
Number of lexical Decl queries : 1
Number of imports initiated by LLDB : 1
Number of imports conducted by Clang : 3
Number of Decls completed : 0
Number of records laid out : 4
-- Local metrics --
Number of visible Decl queries by name : 5
Number of lexical Decl queries : 1
Number of imports initiated by LLDB : 1
Number of imports conducted by Clang : 3
Number of Decls completed : 0
Number of records laid out : 3
[ClangASTImporter] Forgetting destination (ASTContext*)0x7fbedb9aba00
[ClangASTImporter] Forgetting source->dest (ASTContext*)0x7fbedb9aba00->(ASTContext*)0x7fbedab3fa00
== [UserExpression::Evaluate] Executing expression ==
IRMemoryMap::Malloc (16, 0x8, 0x3, eAllocationPolicyHostOnly) -> 0x100036000
IRMemoryMap::Malloc (524288, 0x8, 0x3, eAllocationPolicyHostOnly) -> 0x100037000
IRMemoryMap::Malloc process_sp=0x7fbedaa59e00, process_sp->CanJIT()=true, process_sp->IsAlive()=true
IRMemoryMap::Malloc (4, 0x4, 0x3, eAllocationPolicyMirror) -> 0x100036010
IRMemoryMap::WriteMemory (0x100036000, 0x7fff5f586850, 0x8) went to [0x100036000..0x100036010)
EntityVariable::Materialize [address = 0x100036008, m_variable_sp = item]
IRMemoryMap::WriteMemory (0x100036008, 0x7fff5f586650, 0x8) went to [0x100036000..0x100036010)
Materializer::Materialize (frame_sp = 0x7fbed9ff8f20, process_address = 0x100036000) materialized:
IRMemoryMap::ReadMemory (0x100036000, 0x7fbed9e22270, 0x8) came from [0x100036000..0x100036010)
IRMemoryMap::ReadMemory (0x100036010, 0x7fbed9e2e0b0, 0x4) came from [0x100036010..0x100036014)
0x100036000: EntityResultVariable
Pointer:
0x100036000: 10 60 03 00 01 00 00 00
Temporary allocation:
0x100036010: 00 00 00 00
IRMemoryMap::ReadMemory (0x100036008, 0x7fbed9e22270, 0x8) came from [0x100036000..0x100036010)
0x100036008: EntityVariable
Pointer:
0x100036008: a8 fb bf 5f ff 7f 00 00
Points to process memory:
Module as passed in to IRInterpreter::Interpret:
"; ModuleID = '$__lldb_module'
target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-apple-macosx"
%struct.anon = type { i32 }
; Function Attrs: nounwind
define void @"_Z12$__lldb_exprPv"(i8* %"$__lldb_arg") #0 {
%1 = getelementptr i8, i8* %"$__lldb_arg", i32 8
%2 = bitcast i8* %1 to %struct.anon**
%3 = getelementptr i8, i8* %"$__lldb_arg", i32 0
%4 = bitcast i8* %3 to i32**
%5 = load i32*, i32** %4
%6 = alloca i8*, align 8, !clang.decl.ptr !9
store i8* %"$__lldb_arg", i8** %6, align 8
%7 = icmp eq i8 0, 0
br i1 %7, label %8, label %13
; <label>:8 ; preds = %0
%9 = load %struct.anon*, %struct.anon** %2, align 8
%10 = getelementptr inbounds %struct.anon, %struct.anon* %9, i32 0, i32 0
%11 = load i32, i32* %10, align 4
%12 = sdiv i32 %11, 2
store i32 %12, i32* %5, align 4
br label %13
; <label>:13 ; preds = %8, %0
ret void
}
attributes #0 = { nounwind "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="0" "target-features"="+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
!clang.global.decl.ptrs = !{!0, !1, !0, !2, !3}
!llvm.module.flags = !{!4, !5, !6, !7}
!llvm.ident = !{!8}
!0 = distinct !{null, i64 140457697014984}
!1 = !{void (i8*)* @"_Z12$__lldb_exprPv", i64 140457697013856}
!2 = !{null, i64 140457697014568}
!3 = !{null, i64 140457697014984}
!4 = !{i32 1, !"Objective-C Version", i32 2}
!5 = !{i32 1, !"Objective-C Image Info Version", i32 0}
!6 = !{i32 1, !"Objective-C Image Info Section", !"__DATA, __objc_imageinfo, regular, no_dead_strip"}
!7 = !{i32 4, !"Objective-C Garbage Collection", i32 0}
!8 = !{!"Apple LLVM version 3.8.0 (clang-703.0.29)"}
!9 = !{i64 140457704716640}
"
IRMemoryMap::WriteMemory (0x1000b6ff8, 0x7fff5f585940, 0x8) went to [0x100037000..0x1000b7000)
Made an allocation for argument i8* %"$__lldb_arg"
Data region : 100036000
Ref region : 1000b6ff8
Interpreting %1 = getelementptr i8, i8* %"$__lldb_arg", i32 8
IRMemoryMap::WriteMemory (0x1000b6ff0, 0x7fbed9debe20, 0x8) went to [0x100037000..0x1000b7000)
Interpreted a GetElementPtrInst
P : i8* %"$__lldb_arg" 0x1000b6ff8
Poffset : %1 = getelementptr i8, i8* %"$__lldb_arg", i32 8 0x1000b6ff0
Interpreting %2 = bitcast i8* %1 to %struct.anon**
IRMemoryMap::WriteMemory (0x1000b6fe8, 0x7fbed9debe20, 0x8) went to [0x100037000..0x1000b7000)
Interpreting %3 = getelementptr i8, i8* %"$__lldb_arg", i32 0
IRMemoryMap::WriteMemory (0x1000b6fe0, 0x7fbed9debe20, 0x8) went to [0x100037000..0x1000b7000)
Interpreted a GetElementPtrInst
P : i8* %"$__lldb_arg" 0x1000b6ff8
Poffset : %3 = getelementptr i8, i8* %"$__lldb_arg", i32 0 0x1000b6fe0
Interpreting %4 = bitcast i8* %3 to i32**
IRMemoryMap::WriteMemory (0x1000b6fd8, 0x7fbed9debe20, 0x8) went to [0x100037000..0x1000b7000)
Interpreting %5 = load i32*, i32** %4
IRMemoryMap::ReadMemory (0x1000b6fd8, 0x7fbed9debe20, 0x8) came from [0x100037000..0x1000b7000)
IRMemoryMap::ReadMemory (0x100036000, 0x7fbed9debe20, 0x8) came from [0x100036000..0x100036010)
IRMemoryMap::WriteMemory (0x1000b6fd0, 0x7fbed9debe20, 0x8) went to [0x100037000..0x1000b7000)
Interpreted a LoadInst
P : 0x1000b6fd8
R : 0x100036000
D : 0x1000b6fd0
Interpreting %6 = alloca i8*, align 8, !clang.decl.ptr !9
IRMemoryMap::WriteMemory (0x1000b6fc0, 0x7fff5f5859e0, 0x8) went to [0x100037000..0x1000b7000)
Interpreted an AllocaInst
R : 0x1000b6fc8
P : 0x1000b6fc0
Interpreting store i8* %"$__lldb_arg", i8** %6, align 8
IRMemoryMap::ReadMemory (0x1000b6fc0, 0x7fbed9dec010, 0x8) came from [0x100037000..0x1000b7000)
IRMemoryMap::ReadMemory (0x1000b6ff8, 0x7fbed9dec010, 0x8) came from [0x100037000..0x1000b7000)
IRMemoryMap::WriteMemory (0x1000b6fc8, 0x7fbed9dec010, 0x8) went to [0x100037000..0x1000b7000)
Interpreted a StoreInst
D : 0x1000b6ff8
P : 0x1000b6fc0
R : 0x1000b6fc8
Interpreting %7 = icmp eq i8 0, 0
IRMemoryMap::WriteMemory (0x1000b6fbf, 0x7fbed9dec010, 0x1) went to [0x100037000..0x1000b7000)
Interpreted an ICmpInst
L : i8 0
R : i8 0
= : %7 = icmp eq i8 0, 0 0x1000b6fbf
Interpreting br i1 %7, label %8, label %13
Interpreted a BrInst with a condition
cond : %7 = icmp eq i8 0, 0 0x1000b6fbf
Interpreting %9 = load %struct.anon*, %struct.anon** %2, align 8
IRMemoryMap::ReadMemory (0x1000b6fe8, 0x7fbed9dec010, 0x8) came from [0x100037000..0x1000b7000)
IRMemoryMap::ReadMemory (0x100036008, 0x7fbed9dec010, 0x8) came from [0x100036000..0x100036010)
IRMemoryMap::WriteMemory (0x1000b6fb0, 0x7fbed9dec010, 0x8) went to [0x100037000..0x1000b7000)
Interpreted a LoadInst
P : 0x1000b6fe8
R : 0x100036008
D : 0x1000b6fb0
Interpreting %10 = getelementptr inbounds %struct.anon, %struct.anon* %9, i32 0, i32 0
IRMemoryMap::WriteMemory (0x1000b6fa8, 0x7fbed9dec010, 0x8) went to [0x100037000..0x1000b7000)
Interpreted a GetElementPtrInst
P : %9 = load %struct.anon*, %struct.anon** %2, align 8 0x1000b6fb0
Poffset : %10 = getelementptr inbounds %struct.anon, %struct.anon* %9, i32 0, i32 0 0x1000b6fa8
Interpreting %11 = load i32, i32* %10, align 4
IRMemoryMap::ReadMemory (0x1000b6fa8, 0x7fbed9dec010, 0x8) came from [0x100037000..0x1000b7000)
IRMemoryMap::WriteMemory (0x1000b6fa4, 0x7fbed9dec010, 0x4) went to [0x100037000..0x1000b7000)
Interpreted a LoadInst
P : 0x1000b6fa8
R : 0x7fff5fbffba8
D : 0x1000b6fa4
Interpreting %12 = sdiv i32 %11, 2
IRMemoryMap::WriteMemory (0x1000b6fa0, 0x7fbed9e23180, 0x4) went to [0x100037000..0x1000b7000)
Interpreted a sdiv
L : %11 = load i32, i32* %10, align 4 0x1000b6fa4
R : i32 2
= : %12 = sdiv i32 %11, 2 0x1000b6fa0
Interpreting store i32 %12, i32* %5, align 4
IRMemoryMap::ReadMemory (0x1000b6fd0, 0x7fbed9e23180, 0x8) came from [0x100037000..0x1000b7000)
IRMemoryMap::ReadMemory (0x1000b6fa0, 0x7fbed9e23180, 0x4) came from [0x100037000..0x1000b7000)
IRMemoryMap::WriteMemory (0x100036010, 0x7fbed9e23180, 0x4) went to [0x100036010..0x100036014)
Interpreted a StoreInst
D : 0x1000b6fa0
P : 0x1000b6fd0
R : 0x100036010
Interpreting br label %13
Interpreted a BrInst with no condition
Interpreting ret void
-- [UserExpression::FinalizeJITExecution] Dematerializing after execution --
Materializer::Dematerialize (frame_sp = 0x7fbed9ff8f20, process_address = 0x100036000) about to dematerialize:
IRMemoryMap::ReadMemory (0x100036000, 0x7fbed9e2e0b0, 0x8) came from [0x100036000..0x100036010)
IRMemoryMap::ReadMemory (0x100036010, 0x7fbed9e2e0b0, 0x4) came from [0x100036010..0x100036014)
0x100036000: EntityResultVariable
Pointer:
0x100036000: 10 60 03 00 01 00 00 00
Temporary allocation:
0x100036010: 00 00 00 00
IRMemoryMap::ReadMemory (0x100036008, 0x7fbed9e2e0b0, 0x8) came from [0x100036000..0x100036010)
0x100036008: EntityVariable
Pointer:
0x100036008: a8 fb bf 5f ff 7f 00 00
Points to process memory:
IRMemoryMap::ReadMemory (0x100036000, 0x7fbed9e2e0b0, 0x8) came from [0x100036000..0x100036010)
IRMemoryMap::ReadMemory (0x100036010, 0x7fbed9e23180, 0x4) came from [0x100036010..0x100036014)
IRMemoryMap::Free (0x100036010) freed [0x100036010..0x100036014)
EntityVariable::Dematerialize [address = 0x100036008, m_variable_sp = item]
== [UserExpression::Evaluate] Execution completed normally with result 0 ==
IRMemoryMap::Free (0x100036000) freed [0x100036000..0x100036010)
IRMemoryMap::Free (0x100037000) freed [0x100037000..0x1000b7000)
(int) $0 = 0
EDIT2： 这个问题是从swift.org下载的Ubuntu 14.04的Swift 2.2版本中捆绑的LLDB中的reproduced。
答案 0 :(得分：2)
这显然是一个错误。请在lldb.llvm.org上与bugzilla一起提交。