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[Bug c++/52796] New: [4.6/4.7 C++11] Initialization of primitive object with 0-length parameter pack fails to value-initialize
- From: "jyasskin at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Fri, 30 Mar 2012 20:29:42 +0000
- Subject: [Bug c++/52796] New: [4.6/4.7 C++11] Initialization of primitive object with 0-length parameter pack fails to value-initialize
- Auto-submitted: auto-generated
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52796
Bug #: 52796
Summary: [4.6/4.7 C++11] Initialization of primitive object
with 0-length parameter pack fails to value-initialize
Classification: Unclassified
Product: gcc
Version: 4.7.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned@gcc.gnu.org
ReportedBy: jyasskin@gcc.gnu.org
The following program attempts to initialize a 'char' member using a variadic
parameter pack. With length 0, the initialization doesn't happen, leaving the
original value of the memory in the field. I originally noticed this in gcc-4.6
when std::list<char>(3) failed to initialize the list elements.
$ cat test.cc
#include <memory.h>
#include <iostream>
template<typename T>
class Wrapper {
public:
#if WORK
Wrapper()
: t() {
}
#endif
template<typename ...Args>
Wrapper(Args&&... args)
: t(args...) {
}
T t;
};
int main() {
__attribute__(aligned(alignof(Wrapper<char>))) char
space[sizeof(Wrapper<char>)];
memset(space, '\xab', sizeof(space));
Wrapper<char>*w = new(space) Wrapper<char>;
std::cout << (int)w->t << '\n';
w->~Wrapper<char>();
memset(space, '\xab', sizeof(space));
w = new(space) Wrapper<char>();
std::cout << (int)w->t << '\n';
w->~Wrapper<char>();
memset(space, '\xab', sizeof(space));
w = new(space) Wrapper<char>((int)'y');
std::cout << (int)w->t << '\n';
w->~Wrapper<char>();
}
$ g++-4.7pre --version
g++-4.7pre (GCC) 4.7.1 20120330 (prerelease)
...
$ g++-4.7pre -Wall -std=c++11 test.cc -g3 -o test && ./test
-85
0
121
Disassembling with gdb shows:
Dump of assembler code for function Wrapper<char>::Wrapper<>():
0x0000000000400a70 <+0>: push %rbp
0x0000000000400a71 <+1>: mov %rsp,%rbp
0x0000000000400a74 <+4>: mov %rdi,-0x8(%rbp)
=> 0x0000000000400a78 <+8>: pop %rbp
0x0000000000400a79 <+9>: retq