CODEWITHSUNDEEP
c++clangubsan
zhanxw
zhanxw

Reputation: 3299

Clang++ UBSAN reports invalid value fro type 'std::_Ios_Fmtflags'

The following codes will crash when they are compiled by clang UBSAN

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <sstream>

template<class T>
inline std::string floatToString(T i){
    printf("in floatToString\n");
    std::stringstream ss;
    ss.precision(6);
    ss << std::noshowpoint << i;
    printf("exit floatToString\n");
    return ss.str();
}

int main() {
 std::cout << floatToString(1.0) << "\n";
 return 0;
}

Compile with Clang 3.6:

$> clang++-3.6 -fsanitize=undefined -fno-sanitize=float-divide-by-zero,vptr,function -fno-sanitize-recover -o test test.cpp

Then the program crashed:

$> ./test in floatToString /usr/bin/../lib/gcc/x86_64-linux-gnu/4.8/../../../../include/c++/4.8/bits/ios_base.h:96:24: runtime error: load of value 4294966271, which is not a valid value for type 'std::_Ios_Fmtflags'

Can someone help why this problem happens when I turn on clang UBSAN?

Upvotes: 4

Views: 540

Answers (1)

Thomas
Thomas

Reputation: 3225

It's a bug in libstdc++ according to http://lists.cs.uiuc.edu/pipermail/cfe-dev/2013-January/027401.html.

Still present in libstdc++ 5.1.

libc++ works as expected:

$ clang++ -stdlib=libc++ -fsanitize=undefined -fno-sanitize=float-divide-by-zero,vptr,function -fno-sanitize-recover -o test test.cpp -lc++abi

$ ./test
in floatToString
exit floatToString
1

Upvotes: 1

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