Hi all,
I think I'm also seeing false positives because of vectorization, that
unfortunately decreases the usefulness of valgrind. Below is a minimal
working example that reproduces problems with std::string. The code is
basically extracted from a library I was using (casacore 1.5) and in my
software it generates a lot of incorrect "invalid read"s, although the
library seems to be valid (although inherriting from string would not be
my preferred solution). I hope this example is of use for evaluating the
problem further.
#include <string>
#include <iostream>
#include <cstring>
#include <malloc.h>
class StringAlt : public std::string
{
public:
StringAlt(const char *c) : std::string(c) { }
void operator=(const char *c) { std::string::operator=(c); }
};
typedef StringAlt StringImp;
//typedef std::string StringImp; //<-- replacing prev with this also solves
issue
int main(int argc, char *argv[])
{
const char *a1 = "blaaa";
char *a2 = strdup(a1);
a2[2] = 0;
StringImp s(a1);
std::cout << "Assign A2\n";
s = a2;
std::cout << s << '\n';
std::cout << "Assign A1\n";
s = a1;
std::cout << s << '\n';
char *a3 = strdup(s.c_str());
std::cout << "Assign A3\n";
s = a3;
std::cout << s << '\n';
free(a2);
free(a3);
}
Compiled with g++ Debian 4.7.1-2, with "-O2" or "-O3" results in the
error below. With "-O0", it works fine. Changing the order of statements
can also cause the error to disappear, which makes it very hard to
debug. Output:
Assign A2
bl
Assign A1
blaaa
Assign A3
==20872== Invalid read of size 4
==20872== at 0x400C5C: main (in /home/anoko/projects/test/test)
==20872== Address 0x59550f4 is 4 bytes inside a block of size 6 alloc'd
==20872== at 0x4C28BED: malloc (vg_replace_malloc.c:263)
==20872== by 0x564D911: strdup (strdup.c:43)
==20872== by 0x400C46: main (in /home/anoko/projects/test/test)
==20872==
blaaa
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https://bugs.launchpad.net/bugs/852760
Title:
valgrind false positives on gcc-generated string routines
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