__xstat dynamic symbol resolving error on 64bit - c++

Question

I am trying to dynamically load stat function using dlopen and dlsym.
Functions from stat family are wrapped in corresponding functions __xstat, __xstat64 itp.
Following sniped of code, compiles and works when compiled in 32bit mode (sys/stat.h is included to get stat structure for sake of example)
#include <iostream>
#include <dlfcn.h>
#include <sys/stat.h>
typedef int (*xstat_f) (int __ver, const char *__filename, struct stat *__stat_buf);
int main()
{
auto* h = dlopen("libc.so.6", RTLD_LAZY);
if(!h)
{
return 1; // invalid handle
}
auto f = (xstat_f)dlsym(h, "__xstat");
if(!f)
{
return 1; // invalid handle
}
struct stat s = {};
const auto r = f(3, "/tmp", &s);
if (r != 0)
{
perror("stat");
return errno;
}
return 0;
}
g++ main.cpp -o main -ldl -m32
Executable compiled without -m32 switch on 64bit machine returns EINVAL (Invalid argument).
What is the reason?
Also I've made a minimal test
#include <iostream>
#include <sys/stat.h>
int main(){
struct stat s;
const auto x = stat("/tmp", &s);
if(x != 0) return errno;
return 0;
}
and using objdump -T, on both executables, 32bits and 64bits, shows that stat is resolved as __xstat, so I am using correct symbol. Also I've tried combination of __xstat/__xstat64, struct stat/stat64, same result.

Answer 1

__xstat declarations follows:
int __xstat(int ver, const char *path, (struct stat *stat_buf))
in documentation parameter ver is described like, ver shall be 3 or the behavior of these functions is undefined, which is not entirely true, because in source code, definition of _STAT_VER_LINUX follows:
#ifndef __x86_64__
# define _STAT_VER_LINUX 3
#else
# define _STAT_VER_LINUX 1
#endif
That's why __xstat call on 64bits was failling, parameter ver should have been set to 1, and 3 on 32bits compilation.