https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68175
Bug ID: 68175
Summary: g++ 5.2.1 produces broken executables with
devirtualization enabled
Product: gcc
Version: 5.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ipa
Assignee: unassigned at gcc dot gnu.org
Reporter: bnagaev at gmail dot com
Target Milestone: ---
The following code compiles to a broken executable:
```cpp
#include <fstream>
const int BUFFER_SIZE = 4096;
char buffer_[BUFFER_SIZE];
struct BufferedIfstream : public std::ifstream {
BufferedIfstream() {
rdbuf()->pubsetbuf(buffer_, BUFFER_SIZE);
}
};
int main() {
BufferedIfstream fff;
return 0;
}
```
Compilation command:
$ g++-5 bug.cpp -O2 -o bug.exe
Run it:
$ ./bug.exe
Segmentation fault
Options `-Wall -Wextra` produce no warnings.
Options `-fno-strict-aliasing -fwrapv` change nothing.
Without `-O2` (or `-O3`) the bug disappears.
With `-fno-devirtualize` the bug disappears.
With `-O1` the bug disappears but with `-O1 -fdevirtualize` appears again.
Without a class the bug disappears. The following code works correctly:
```cpp
#include <fstream>
const int BUFFER_SIZE = 4096;
char buffer_[BUFFER_SIZE];
int main() {
std::ifstream fff;
fff.rdbuf()->pubsetbuf(buffer_, BUFFER_SIZE);
return 0;
}
```
I have reproduced this bug in gcc 5.1.0, 5.2.0 (MXE build, MinGW-w64 [1]) and
in gcc 5.2.1 (Debian Stretch, amd64 Linux, 5.2.1-22). I believe this bug was
introduced in gcc 5, when devirtualization was refactored [2].
The issue seems to be related to the mailing thread about -O3 (MXE): stack
smashing on i686 with -O3 since da82d07dbe [3].
[1] https://github.com/mxe/mxe/issues/964
[2] https://gcc.gnu.org/gcc-5/changes.html
[3]
http://lists.nongnu.org/archive/html/mingw-cross-env-list/2015-10/msg00020.html
