В докладе будет разобрано, что-же такое ODR, какие ошибки могут быть из-за нарушения этого правила. Также будет представлен Proof-of-concept утилиты на базе clang tooling по автоматическому поиску таких ошибок.

1. ONE DEFINITION RULE – HOW TO LIVE WITH IT
Alexey Kutumov
Software engineer at Kaspersky Lab

2. CONTENTS
2
И ЦИЯ
И Е Ы
CLANG/ODR-CHECK3
2
1

3. И ЦИЯ

4. ODR-CHECK
4
Compilation/linking
compile
compile
compile
.cpp .obj .exe
.cpp .obj
.cpp .obj
ar
.lib
link

5. И ЦИЯ
5
enumeration
enum Foo {
e1,
e2,
eCount
};
const char* FooToString(Foo x);
int main() {
std::cout << FooToString(e2) << std::endl;
return 0;
}
enum Foo {
e1,
eCount
};
const char xxx [] = «can you see me?!!»
const char* msg [eCount] = {
«e1»
};
const char* canYouSeeMe = xxx;
const char* FooToString(Foo x) {return msg[x];}

6. И ЦИЯ
6
struct A : private boost::noncopyable {
A() : x(«0») {}
const std::string x;
int y;
};
void Modify(A& a);
int main() {
A a;
Modify(a);
std::cout << a.x << std::endl;
return 0;
}
struct A : private boost::noncopyable {
A();
int x;
const std::string y;
};
void Modify(A& a) {
a.x += 1;
}

7. И ЦИЯ
7
pragma pack
#pragma pack(push, 1)
struct C {
char c;
uint32_t x;
};
#pragma pack(pop)
void Modify(C* c, size_t pos);
int main() {
std::string x = «0»;
C c[8] = {0};
Modify(c, 6);
std::cout << x << std::endl;
return 0;
}
struct C {
char c;
uint32_t x;
};
void Modify(C* c, size_t pos) {
c[pos].x += 1;
}

8. И ЦИЯ
8
К
• , ,
• + Х assert, core dump, ,
• - « »
•Code review
• - ,
•gcc –Wodr, gold –detect-odr-violations
• +
• - , false positive
•Amalgamation (sqlite)
• +
• -
• -

9. И Е Ы

10. И Е Ы
10
3.2 C++
• , , ,
• non-inline ODR-
used
• , ,
complete.

11. И Е Ы
11
3.2 C++
• non-inline
ODR-used.
• , , inline external
linkage, , . :
• К
• В , TU

12. И Е Ы
12
3.2 C++
Undefined Behavior

13. И Е Ы
13
Т
•А
•
•Т IDE, .

14. И Е Ы
14
#pragma detect_mismatch
#pragma detect_mismatch(«my_name», «my_value1») /// cpp1.cpp
#pragma detect_mismatch(«my_name», «my_value2») /// cpp2.cpp
cpp2.obj : error LNK2038: mismatch detected for 'my_name': value ‘my_value ' doesn't match value ‘my_value '
in cpp1.obj
dumpbin /ALL cpp1.obj
Linker Directives
-----------------
/FAILIFMISMATCH:"my_name=my_value1"
/DEFAULTLIB:"MSVCRTD"
/DEFAULTLIB:"OLDNAMES"

15. CLANG/ODR-CHECK

16. CLANG
16
clang

17. ODR-CHECK
17
Compilation/linking
compile
compile
compile
.cpp .obj .exe
.cpp .obj
.cpp .obj
ar
.lib
link

18. ODR-CHECK
18
Checking for ODR violations
emit-ast
emit-ast
emit-ast
.cpp .ast .ast
.cpp .ast
.cpp .ast
merge-ast
.ast
merge-ast

19. ODR-CHECK
19
Compilation
http://clang.llvm.org/docs/IntroductionToTheClangAST.html
http://clang.llvm.org/docs/InternalsManual.html
.cpp
token
stream
ASTContext
Preprocessor/Lexer Sema
LLVM IR
ASTFrontendAction
(CodeGenAction)

20. ODR-CHECK
20
Storing AST to file
.cpp
token
stream
ASTContext
Preprocessor/Lexer Sema
.ast
ASTFrontendAction
(GeneratePCHAction)

21. ODR-CHECK
21
Merging ASTs
cannot import unsupportОН noНО: …
.ast
.ast
.ast
.ast
ASTMergeAction

22. ODR-CHECK
22
Merging ASTs
• :
•
•
• ODR,
•

23. ODR-CHECK
23
RecursiveASTVisitor
namespace m {
struct X {
int a;
};
}
clang ../main.cpp -Xclang -ast-dump -fsyntax-only
http://clang.llvm.org/docs/RAVFrontendAction.html

24. ODR-CHECK
24
ASTImporter
TranslationUnitDecl (From) TranslationUnitDecl (To)
|-Node |-Node
`-Node `-Node
`-Node `-Node
ASTNodeImporter

25. ODR-CHECK
25
ASTNodeImporter
namespace m { /// 4. NamespaceDecl(NamedDecl, DeclContext)
namespace n { /// 3. NamespaceDecl (NamedDecl, DeclContext)
struct X { /// 2. CXXRecordDecl (..., TypeDecl, DeclContext)
struct Y { /// 1. CXXRecordDecl (..., TypeDecl, DeclContext)
int a; /// <- IMPORT
};
};
}
}

26. ODR-CHECK
26
StructuralEquivalenceContext
namespace m {
struct X {
int a;
long b;
};
struct Y {
X x;
int b;
};
struct Z {
int b;
};
}
namespace m {
struct X {
int a;
long b;
};
struct Y {
X x;
long b;
};
struct Z {
int a;
};
}

27. ODR-CHECK
27
И cmake
clang++ -DMY_SUPER_DEFINE –Wall –I/my/include –emit-ast source_file.cpp –o source_file.ast
clang++ -cc1 –emit-pch –o lib_file.ast -ast-merge source_file1.ast –ast-merge source_file2.ast
cmake ../src -DCMAKE_TOOLCHAIN_FILE=d:/tools/ClangOdrCheckToolchain.cmake –D...
make

28. ODR-CHECK
28
Sample output
namespace m {
struct X {
int x;
#if defined (M1)
int z;
#endif /* M1 */
};
}

29. ODR-CHECK
29
Sample output
In file included from d:pixelprojectsodr-checkodr-check-testsrcdatasrcm1.cpp:3:
d:pixelprojectsodr-checkodr-check-testsrcdatasrc/h1.h:11:8: warning: type 'struct m::X' has
incompatible definitions in different translation units
struct X
^
d:pixelprojectsodr-checkodr-check-testsrcdatasrc/h1.h:16:7: note: field 'z' has type 'int' here
int z;
^
d:pixelprojectsodr-checkodr-check-testsrcdatasrc/h1.h:11:8: note: no corresponding field here
struct X
^

30. ODR-CHECK
30
ИТ
• PoC: https://github.com/prograholic/clang/tree/odr-check
• Production Ready (milestone: check tool on some Boost libraries)
• Memory consumption (huge ASTs)
• Minimize import amount (static, unnamed namespaces, templates)
•Merge changes to clang/master

31. LET'S TALK?
mail: alexey.kutumov@gmail.com
twitter: @prograholic
https://github.com/prograholic/odr-check
https://github.com/prograholic/clang/tree/odr-check