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Date: Fri, 03 Oct 2014 10:09:00 -0000
From: =?UTF-8?B?SGVucmlrIE1hbm5lcnN0csO2bQ==?= <henrik.mannerstrom@gmail.com>
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To: Jonathan Wakely <jwakely.gcc@gmail.com>
CC: gcc-help <gcc-help@gcc.gnu.org>
Subject: Re: std::string clobbers memory when compiling without optimizations
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Hi,

On 10/03/2014 12:58 PM, Jonathan Wakely wrote:
> Have you tried valgrind? Or compiling with GCC's -fstack-protector
> option? I can't reproduce the problem, and I think it's pretty
> unlikely std::string has that kind of bug without someone noticing
> years ago. 

I'm not assuming that std::string has a bug (even though the title might
suggest that), I'm just saying that the gdb watchpoint is triggered
inside that function. I tried valgrind memcheck, but I'm no expert, so
suggestions are welcome. Below is the output with stack-protector, what
do you make out of it? Could it be my installation?

- Henrik


$ g++-4.9 -std=gnu++1y mvu.cc  -o mvu
$ ./mvu
Correct diagonal: 1 1 1
Eigen::Matrix<double, 1, 3, 1, 1, 3>
Incorrect diagonal: 1.81749e-316            1            1
$ g++-4.9 -std=gnu++1y -fstack-protector-all mvu.cc  -o mvu
$ ./mvu
Correct diagonal: 1 1 1
Eigen::Matrix<double, 1, 3, 1, 1, 3>
Incorrect diagonal: 1 2 3
$ g++-4.9 -std=gnu++1y -O1 -fstack-protector-all  mvu.cc  -o mvu
$ ./mvu
Correct diagonal: 1 1 1
Eigen::Matrix<double, 1, 3, 1, 1, 3>
Incorrect diagonal: 1 1 1

g++-4.9 (Ubuntu 4.9.1-3ubuntu2~14.04.1) 4.9.1
Copyright (C) 2014 Free Software Foundation, Inc.