Using memory sanitizer with libstdc++

Question

I wish to use the -fsanitize=memory flag in clang to analyse a program like the following:

#include <string> #include <iostream> #include <fstream> using namespace std;  void writeToFile(){     ofstream o;     o.open("dum");     o<<"test"<<endl; //The error is here.                      //It does not matter if the file is opened this way,                      //or with o("dum");     o.close(); } int main(){     writeToFile(); } 

As far as I know, this program is correct, but when I use clang++ san.cpp -fsanitize=memory It fails (at runtime) with:

UMR in __interceptor_write at offset 0 inside [0x64800000e000, +5)   ==9685== WARNING: MemorySanitizer: use-of-uninitialized-value       #0 0x7f48d0899ae5 (/usr/lib/x86_64-linux-gnu/libstdc++.so.6+0x7bae5)       #1 0x7f48d08d1787 (/usr/lib/x86_64-linux-gnu/libstdc++.so.6+0xb3787)       #2 0x7f48d08d21e2 (/usr/lib/x86_64-linux-gnu/libstdc++.so.6+0xb41e2)       #3 0x7f48d08cfd1e (/usr/lib/x86_64-linux-gnu/libstdc++.so.6+0xb1d1e)       #4 0x7f48d08b1f2d (/usr/lib/x86_64-linux-gnu/libstdc++.so.6+0x93f2d)       #5 0x7f48d16d60f5 in writeToFile() /home/daniel/programming/test/santest.cpp:10       #6 0x7f48d16d61f4 in main /home/daniel/programming/test/santest.cpp:15       #7 0x7f48d0261de4 (/lib/x86_64-linux-gnu/libc.so.6+0x21de4)       #8 0x7f48d16d5e42 in _start (/home/daniel/programming/test/a.out+0x61e42)    SUMMARY: MemorySanitizer: use-of-uninitialized-value ??:0 ?? 

How can I make this work properly?

Clang version 3.5, stdlibc++ version 6

Answer 1

The code is fine, of course but many similar errors are cause by the following requirement of clang's memory sanitizer tool:

MemorySanitizer (without a dynamic component) requires that the entire program code including libraries, (except libc/libm/libpthread, to some extent), is instrumented.

from here

The cplusplus runtime you are using libstdc++ is unistrumented and causes errors. You will unfortunately have to follow a somewhat fiddly process as described at that link to rebuild an instrumented libstdc++ or switch to libc++ (easier-ish)

Answer 2

There easiest way at this time is to build libc++ with memorysanitizer, then link your program against it.

This is how I did it some time ago, failing to handle libc++ build system: https://code.google.com/p/memory-sanitizer/source/browse/bootstrap/build_libcxx.sh

I heard there've been improvements on the libc++ side, maybe it would be possible to build it as usual (with something like CC=/path/to/clang CFLAGS=-fsanitize=memory).