C++ Program Always Crashes While doing a std::stri

问题:

I have been trying to debug a crash in my application that crashes (i.e. asserts a * glibc detected * free(): invalid pointer: 0x000000000070f0c0 ***) while I'm trying to do a simple assign to a string. Note that I'm compiling on a linux system with gcc 4.2.4 with an optimization level set to -O2. With -O0 the application no longer crashes.

E.g.

std::string abc;

abc = "testString";

but if I changed the code as follows it no longer crashes

std::string abc("testString");

So again I scratched my head! But the interesting pattern was that the crash moved later on in the application, AGAIN at another string. I found it weird that the application was continuously crashing on a string assign. A typical crash backtrace would look as follows:

#0  0x00007f2c2663bfb5 in raise () from /lib64/libc.so.6
(gdb) bt
#0  0x00007f2c2663bfb5 in raise () from /lib64/libc.so.6
#1  0x00007f2c2663dbc3 in abort () from /lib64/libc.so.6
#2  0x00000000004d8cb7 in people_streamingserver_sighandler (signum=6) at src/peoplestreamingserver.cpp:487
#3  <signal handler called>
#4  0x00007f2c2663bfb5 in raise () from /lib64/libc.so.6
#5  0x00007f2c2663dbc3 in abort () from /lib64/libc.so.6
#6  0x00007f2c26680ce0 in ?? () from /lib64/libc.so.6
#7  0x00007f2c270ca7a0 in std::string::assign (this=0x7f2c21bc8d20, __str=<value optimized out>)
    at /home/bbazso/ThirdParty/sources/gcc-4.2.4/x86_64-pc-linux-gnu/libstdc++-v3/include/bits/basic_string.h:238
#8  0x00007f2c21bd874a in PEOPLESProtocol::GetStreamName (this=<value optimized out>,
    pRawPath=0x2342fd8 "rtmp://127.0.0.1/mp4:pop.mp4", lStreamName=@0x7f2c21bc8d20)
    at /opt/trx-HEAD/gcc/4.2.4/lib/gcc/x86_64-pc-linux-gnu/4.2.4/../../../../include/c++/4.2.4/bits/basic_string.h:491
#9  0x00007f2c21bd9daa in PEOPLESProtocol::SignalProtocolCreated (pProtocol=0x233a4e0, customParameters=@0x7f2c21bc8de0)
    at peoplestreamer/src/peoplesprotocol.cpp:240

This was really weird behavior and so I started to poke around further in my application to see if there was some sort of memory corruption (either heap or stack) error that could be occurring that could be causing this weird behavior. I even checked for ptr corruptions and came up empty handed. In addition to visual inspection of the code I also tried the following tools:

• Valgrind using both memcheck and exp-ptrcheck
• electric fence
• libsafe
• I compiled with -fstack-protector-all in gcc
• I tried MALLOC_CHECK_ set to 2
• I ran my code through lint checks as well as cppcheck (to check for mistakes)
• And I stepped through the code using gdb

So I tried a lot of stuff and still came up empty handed. So I was wondering if it could be something like a linker issue or a library issue of some sort that could be causing this problem. Are there any know issues with the std::string that make is susceptible to crashing in -O2 or maybe it has nothing to do with the optimization level? But the only pattern that I can see thus far in my problem is that it always seems to crash on a string and so I was wondering if anyone knew of any issues that my be causing this type of behavior.

Thanks a lot!

回答1:

This is an initial guess using all information I can extract from your back trace.

You are most likely mixing and matching gcc version, linker and libstdc++ that results an unusual behaviour on the host machine:

1. libc is the system's: /lib64/libc.so.6
2. libstdc++ is in a "ThirdParty" directory - this is suspicions, as it tells me it might be compiled elsewhere with a different target - /home/bbazso/ThirdParty/sources/gcc-4.2.4/x86_64-pc-linux-gnu/libstdc++-v3/
3. Yet another libstdc++ in /opt: /opt/trx-HEAD/gcc/4.2.4/lib/gcc/x86_64-pc-linux-gnu/4.2.4/../../../../include/c++/4.2.4/bits/basic_string.h:491

In addition, GCC may mix the system's ld instead of itself which may cause further weird memory maps usage.

回答2:

Can you repeat the crash with a basic two line program?

#include <string>

int main()
{
    std::string abc;
    abc = "testString";
}

If that crashes, please post your exact compile / link options?

If not, start paring down your code. Remove things lines a handful at a time until the bug goes away. Once you have some other change you can add to cause the crash and remove to make it go away, that should help you locate the problem.

回答3:

Happened to me because of using malloc for a class which had std::strings as data members. Tricky.

回答4:

As you said it's a weird behavior.

To be honnest with i think you are wasting time looking into a possible bug with std::strings. Strings are perfectly safe as long as you are using them well.

Anyway, with the informations you are giving : First, are you using threads ? It's might be a thread problem. Second, you check your program using valgrind. Have you no warnings at all ?

Note : The most critical valgrind's warnings are invalid read and invalid write.

PS : As said in commentary, you should probably use g++ to compile C++ code ;)