[cfe-dev] Is this a bug or just illegal code
don hinton via cfe-dev
cfe-dev at lists.llvm.org
Thu Jun 8 11:05:37 PDT 2017
I'm seeing memory corruption when I use a literal string and std::string in
a ternary (?:) expression. If I change ss to ss.c_str() on line 5, the
corruption goes away. [1] is an AST diff, which might help explain it.
Although clang doesn't give me an error or warning, is this code legal, or
is this a bug?
thanks...
don
$ grep -n "." x.cpp
1:#include "llvm/ADT/StringRef.h"
3:int main() {
4: const std::string ss;
5: llvm::StringRef Ref = true ? "noexcept" : ss;
6: std::string s = Ref;
7: return 0;
8:}
$ ../../4.0.0/build/Release/bin/clang++ x.cpp -O1 -g -fsanitize=address
-fno-omit-frame-pointer -std=c++11 -I ../../llvm/include/ -I include
$ ./a.out
=================================================================
==14769==ERROR: AddressSanitizer: heap-use-after-free on address
0x604000000068 at pc 0x0000004651b2 bp 0x7ffcc5b3a7d0 sp 0x7ffcc5b39f80
READ of size 8 at 0x604000000068 thread T0
#0 0x4651b1 in __interceptor_memcpy.part.36
/home/d80049854/projects/clang/4.0.0/llvm/projects/compilerr
t/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc:655
#1 0x7f00fe4d10ed (/usr/lib/x86_64-linux-gnu/libstdc++.so.6+0xc40ed)
#2 0x7f00fe4d298a in std::basic_string<char, std::char_traits<char>,
std::allocator<char> >::basic_string(char const*, unsigned long,
std::allocator<char> const&) (/usr/lib/x86_64-linux-gnu/lib
stdc++.so.6+0xc598a)
#3 0x50d3bc in llvm::StringRef::str() const
/home/d80049854/projects/clang/build/Debug/../../llvm/includ
e/llvm/ADT/StringRef.h:230:14
#4 0x50d2cd in llvm::StringRef::operator std::string() const
/home/d80049854/projects/clang/build/Debug/../../llvm/includ
e/llvm/ADT/StringRef.h:257:14
#5 0x50d0aa in main /home/d80049854/projects/clang
/build/Debug/x.cpp:6:19
#6 0x7f00fd522f44 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so
.6+0x21f44)
#7 0x41a10b in _start (/home/d80049854/projects/clan
g/build/Debug/a.out+0x41a10b)
0x604000000068 is located 24 bytes inside of 33-byte region
[0x604000000050,0x604000000071)
freed by thread T0 here:
#0 0x5098b0 in operator delete(void*) /home/d80049854/projects/clang
/4.0.0/llvm/projects/compiler-rt/lib/asan/asan_new_delete.cc:126
#1 0x7f00fe4d11cd in std::basic_string<char, std::char_traits<char>,
std::allocator<char> >::~basic_string() (/usr/lib/x86_64-linux-gnu/lib
stdc++.so.6+0xc41cd)
#2 0x7f00fd522f44 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so
.6+0x21f44)
previously allocated by thread T0 here:
#0 0x508b70 in operator new(unsigned long)
/home/d80049854/projects/clang/4.0.0/llvm/projects/compiler-
rt/lib/asan/asan_new_delete.cc:82
#1 0x7f00fe4d0f68 in std::string::_Rep::_S_create(unsigned long,
unsigned long, std::allocator<char> const&) (/usr/lib/x86_64-linux-gnu/lib
stdc++.so.6+0xc3f68)
SUMMARY: AddressSanitizer: heap-use-after-free
/home/d80049854/projects/clang/4.0.0/llvm/projects/compiler-
rt/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc:655 in
__interceptor_memcpy.part.36
Shadow bytes around the buggy address:
0x0c087fff7fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c087fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c087fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c087fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c087fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c087fff8000: fa fa 00 00 00 00 00 01 fa fa fd fd fd[fd]fd fa
0x0c087fff8010: fa fa 00 00 00 00 01 fa fa fa fa fa fa fa fa fa
0x0c087fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c087fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c087fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c087fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
Addressable: 00
Partially addressable: 01 02 03 04 05 06 07
Heap left redzone: fa
Freed heap region: fd
Stack left redzone: f1
Stack mid redzone: f2
Stack right redzone: f3
Stack after return: f5
Stack use after scope: f8
Global redzone: f9
Global init order: f6
Poisoned by user: f7
Container overflow: fc
Array cookie: ac
Intra object redzone: bb
ASan internal: fe
Left alloca redzone: ca
Right alloca redzone: cb
==14769==ABORTING
1. AST diff:
< uses ss
> uses ss.c_str()
49566c49566
< | | |-CXXConstructorDecl 0xXXXXXXX <line:3010:7, col:XX> col:XX used
basic_string 'void (const char *, const class std::allocator<char> &)'
---
> | | |-CXXConstructorDecl 0xXXXXXXX <line:3010:7, col:XX> col:XX
basic_string 'void (const char *, const class std::allocator<char> &)'
49568,49573c49568
< | | | `-ParmVarDecl 0xXXXXXXX <col:XX, col:XX> col:XX __a 'const class
std::allocator<char> &' cinit
< | | | `-ExprWithCleanups 0xXXXXXXX <col:XX, col:XX> 'const class
std::allocator<char>':'const class std::allocator<char>' lvalue
< | | | `-MaterializeTemporaryExpr 0xXXXXXXX <col:XX, col:XX> 'const
class std::allocator<char>':'const class std::allocator<char>' lvalue
< | | | `-ImplicitCastExpr 0xXXXXXXX <col:XX, col:XX> 'const class
std::allocator<char>':'const class std::allocator<char>' <NoOp>
< | | | `-CXXBindTemporaryExpr 0xXXXXXXX <col:XX, col:XX> 'class
std::allocator<char>':'class std::allocator<char>' (CXXTemporary 0xXXXXXXX)
< | | | `-CXXTemporaryObjectExpr 0xXXXXXXX <col:XX, col:XX>
'class std::allocator<char>':'class std::allocator<char>' 'void (void)
throw()'
---
> | | | `-ParmVarDecl 0xXXXXXXX <col:XX, col:XX> col:XX __a 'const class
std::allocator<char> &'
108945c108940
< | | |-CXXConstructorDecl 0xXXXXXXX
<../../llvm/include/llvm/Support/Compiler.h:194:38,
../../llvm/include/llvm/ADT/StringRef.h:96:49> line:95:18 used StringRef
'void (const std::string &)'
---
> | | |-CXXConstructorDecl 0xXXXXXXX <../../llvm/include/llvm/Support/Compiler.h:194:38,
../../llvm/include/llvm/ADT/StringRef.h:96:49> line:95:18 StringRef 'void
(const std::string &)'
111747,111765c111742,111749
< | `-CXXConstructExpr 0xXXXXXXX <col:XX, col:XX>
'llvm::StringRef':'class llvm::StringRef' 'void (const std::string &)'
< | `-MaterializeTemporaryExpr 0xXXXXXXX <col:XX, col:XX>
'const std::string':'const class std::basic_string<char>' lvalue
< | `-ConditionalOperator 0xXXXXXXX <col:XX, col:XX>
'const std::string':'const class std::basic_string<char>'
< | |-CXXBoolLiteralExpr 0xXXXXXXX <col:XX> '_Bool' true
< | |-CXXBindTemporaryExpr 0xXXXXXXX <col:XX> 'const
std::string':'const class std::basic_string<char>' (CXXTemporary 0xXXXXXXX)
< | | `-CXXConstructExpr 0xXXXXXXX <col:XX> 'const
std::string':'const class std::basic_string<char>' 'void (const class
std::basic_string<char> &)' elidable
< | | `-MaterializeTemporaryExpr 0xXXXXXXX <col:XX>
'const std::string':'const class std::basic_string<char>' lvalue
< | | `-CXXBindTemporaryExpr 0xXXXXXXX <col:XX>
'const std::string':'const class std::basic_string<char>' (CXXTemporary
0xXXXXXXX)
< | | `-CXXConstructExpr 0xXXXXXXX <col:XX>
'const std::string':'const class std::basic_string<char>' 'void (class
std::basic_string<char> &&) noexcept' elidable
< | | `-MaterializeTemporaryExpr 0xXXXXXXX
<col:XX> 'std::string':'class std::basic_string<char>' xvalue
< | | `-CXXBindTemporaryExpr 0xXXXXXXX
<col:XX> 'std::string':'class std::basic_string<char>' (CXXTemporary
0xXXXXXXX)
< | | `-ImplicitCastExpr 0xXXXXXXX <col:XX>
'std::string':'class std::basic_string<char>' <ConstructorConversion>
< | | `-CXXConstructExpr 0xXXXXXXX
<col:XX> 'std::string':'class std::basic_string<char>' 'void (const char *,
const class std::allocator<char> &)'
< | | |-ImplicitCastExpr 0xXXXXXXX
<col:XX> 'const char *' <ArrayToPointerDecay>
< | | | `-StringLiteral 0xXXXXXXX
<col:XX> 'const char [9]' lvalue "noexcept"
< | | `-CXXDefaultArgExpr 0xXXXXXXX
<<invalid sloc>> 'const class std::allocator<char>':'const class
std::allocator<char>' lvalue
< | `-CXXBindTemporaryExpr 0xXXXXXXX <col:XX> 'const
std::string':'const class std::basic_string<char>' (CXXTemporary 0xXXXXXXX)
< | `-CXXConstructExpr 0xXXXXXXX <col:XX> 'const
std::string':'const class std::basic_string<char>' 'void (const class
std::basic_string<char> &)'
< | `-DeclRefExpr 0xXXXXXXX <col:XX> 'const
std::string':'const class std::basic_string<char>' lvalue Var 0xXXXXXXX
'ss' 'const std::string':'const class std::basic_string<char>'
---
> | `-CXXConstructExpr 0xXXXXXXX <col:XX, col:XX>
'llvm::StringRef':'class llvm::StringRef' 'void (const char *)'
> | `-ConditionalOperator 0xXXXXXXX <col:XX, col:XX> 'const
char *'
> | |-CXXBoolLiteralExpr 0xXXXXXXX <col:XX> '_Bool' true
> | |-ImplicitCastExpr 0xXXXXXXX <col:XX> 'const char *'
<ArrayToPointerDecay>
> | | `-StringLiteral 0xXXXXXXX <col:XX> 'const char [9]'
lvalue "noexcept"
> | `-CXXMemberCallExpr 0xXXXXXXX <col:XX, col:XX> 'const
char *'
> | `-MemberExpr 0xXXXXXXX <col:XX, col:XX> '<bound
member function type>' .c_str 0xXXXXXXX
> | `-DeclRefExpr 0xXXXXXXX <col:XX> 'const
std::string':'const class std::basic_string<char>' lvalue Var 0xXXXXXXX
'ss' 'const std::string':'const class std::basic_string<char>'
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