why initstate_r crashes when using variables on the stack - c++

Question

Sorry this question not end yet.
I'm trying to write a thread-safe random generator, but
it crashes at
initstate_r(time(NULL), m_state_buff, sizeof(m_state_buff), &m_data);
My gcc version:
gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <time.h>
class RandomGenerator
{
public:
RandomGenerator()
{
initstate_r(time(NULL), m_state_buff, sizeof(m_state_buff), &m_data);
}
virtual ~RandomGenerator() {}
public:
int32_t get_next_int()
{
#ifdef __GNUC__
static __thread char stat_buff[512];
static __thread random_data buff;
static __thread bool inited = false;
if (!inited)
{
initstate_r(time(NULL), stat_buff, sizeof(stat_buff), &buff);
srandom_r(time(NULL), &buff);
inited = true;
}
int32_t result = 0;
random_r(&buff, &result);
return result;
#endif
}
private:
struct random_data m_data;
char m_state_buff[512];
};
int main()
{
RandomGenerator r;
for (int i = 0; i < 100; ++i)
{
printf("%d\n", r.get_next_int());
}
}

Answer 1

I believe this related to the libc initstate_r() 's bug.
An initialization method should not re-use the buffer's value, it should clean it first.
When I cleanup the buffer before call initstate_r() the segmentation fault has gone.
#include <stdlib.h>
#include <stdint.h>
#include <stdio.h>
#include <time.h>
#include <string.h>
class RandomGenerator
{
public:
RandomGenerator()
{
memset(m_state_buff, 0, sizeof(m_state_buff));
memset(&m_data, 0, sizeof(m_data);
initstate_r(time(NULL), m_state_buff, sizeof(m_state_buff), &m_data);
}
virtual ~RandomGenerator() {}
private:
struct random_data m_data;
char m_state_buff[512];
};
int main()
{
RandomGenerator r;
for (int i = 0; i < 100; ++i)
{
printf("%d\n", r.get_next_int());
}
}