Why does asan Intercept vfork() ?

[Zhenhang1213]

Why does asan Intercept vfork() ? using options -lpthread -fsanitize=address -fsanitize=undefined, clang 15.0.4

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <pthread.h>
#include <wait.h>

void *TestPopen(void *arg)
{
printf("hello TestPopen.\n");
pid_t pid = vfork();
if (pid < 0) {
printf("error vfork.\n");
} else if (pid == 0) {
printf("I'm child.\n");
pid_t childPid = vfork();
if (childPid < 0) {
printf("error vfork.\n");
} else if (childPid == 0) {
// vfork a grand processes
printf("I'm grand child, and call exit(0).\n");
_exit(0);
} else {
printf("I'm child vfork, and call exit(0).\n");
_exit(0);
}
} else {
// father Processes
printf("I'm parent.\n");
}
while(1) {
sleep(1);
}
return NULL;
}

int main()
{
printf("hello\n");
pthread_t tid;
int ret = pthread_create(&tid, NULL, TestPopen, NULL);
printf("create pthread ret %d.\n", ret);
while(1) {
sleep(1);
}
return 0;
}

The result is not same without asan