[Qemu-devel] [Bug 1035572] Re: Bug in Qemu User Mode

[Jens Melzer <melzer.jens@gmail.com>]

*** This bug is a duplicate of bug 739785 ***
    https://bugs.launchpad.net/bugs/739785

** This bug has been marked a duplicate of bug 739785
   qemu-i386 user mode can't fork (bash: fork: Invalid argument)

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https://bugs.launchpad.net/bugs/1035572

Title:
  Bug in Qemu User Mode

Status in QEMU:
  New

Bug description:
  Hi,
  I make an interesting discovery.
  My aim is to have a working qemu-i386 on Raspberry Pi.
  After long searching in the dark what goes wrong with ANY Qemu version for User Mode until today,
  I find the following: The bug must be in at least one function, that the program testclone
  from the testpackage for i386 in linux-user-test-0.3 calls.
  The wrong function is in the part, which enables more than one thread at the same time, NPTL.
  Funny, how I find this out: All the programs from the tests in linux-user-test-0.3 I can now run succesfull with my new builded qemu-i386 for Raspi.
  But the program testclone does not stop after it gives out all the right messages.
  The program testclone stops on my Desktop computer with Debian Wheezy installed.
  So, the error is not in the program testclone.
  So I make a look, what is going on there with strace. With strace you get informations about all the values in the working program, here testclone.
  I see, that the reason, why testclone not stops is in an infinite loop because of 
  while (waitpid(pid1, &status1, 0) != pid1);
  while (waitpid(pid2, &status2, 0) != pid2);
  at its end is never fullfilled. 
  This is the reason for the famous error message from Qemu User Mode 

  qemu: uncaught target signal 11 (Segmentation fault) - core dumped 
  Segmentation fault 

  stack1 = malloc(STACK_SIZE);
  pid1 = clone(thread1_func, stack1 + STACK_SIZE,
  CLONE_VM | CLONE_FS | CLONE_FILES | SIGCHLD, "hello1");

  stack2 = malloc(STACK_SIZE);
  pid2 = clone(thread2_func, stack2 + STACK_SIZE, 
  CLONE_VM | CLONE_FS | CLONE_FILES | SIGCHLD, "hello2");

  The error happens early in the program testclone. Strace says, it is because no childprocess at all can be found. So, some basiccalculations in those four lines must be done wrong from Qemu.
  I think, that the adressspace for each thread is calculated wrong, or overlapps.
  Funny, it has nothing to do with the ARM processor. I get exact the same errormessages, when I run the program testclone on my desktopcompi i386 with a Wheezy in Qemu and then qemu-i386 testclone.
  This is a good message, because it means it is an error, that belongs at least to the i386 family but I think, every processor in Qemu User Mode is involved, so until now NPTL does not work.
  Today I make a hand by hand calculation with the source code from testclone and compare it with the values, that Qemu User Mode give. The handcalculated values should  be the same which my 
  Desktop computer with Wheezy with tesclone produces, but who knows,
  Dietmar

  PS: I hope, that this is the right source code for testclone. Any help
  is welcome:-)!

  
  Code: Select all
  #include <stdlib.h>
  #include <stdio.h>
  #include <string.h>
  #include <signal.h>
  #include <unistd.h>
  #include <inttypes.h>
  #include <pthread.h>
  #include <sys/wait.h>
  #include <sched.h>

  int thread1_func(void *arg)
  {
      int i;
      char buf[512];

      for(i=0;i<10;i++) {
          snprintf(buf, sizeof(buf), "thread1: %d %s\n", i, (char *)arg);
         write(1, buf, strlen(buf));
          usleep(100 * 1000);
      }
      return 0;
  }

  int thread2_func(void *arg)
  {
      int i;
      char buf[512];
      for(i=0;i<20;i++) {
          snprintf(buf, sizeof(buf), "thread2: %d %s\n", i, (char *)arg);
          write(1, buf, strlen(buf));
          usleep(120 * 1000);
      }
      return 0;
  }

  #define STACK_SIZE 16384

  void test_clone(void)
  {
      uint8_t *stack1, *stack2;
      int pid1, pid2, status1, status2;

      stack1 = malloc(STACK_SIZE);
      pid1 = clone(thread1_func, stack1 + STACK_SIZE, 
                   CLONE_VM | CLONE_FS | CLONE_FILES | SIGCHLD, "hello1");

      stack2 = malloc(STACK_SIZE);
      pid2 = clone(thread2_func, stack2 + STACK_SIZE, 
                  CLONE_VM | CLONE_FS | CLONE_FILES | SIGCHLD, "hello2");

      while (waitpid(pid1, &status1, 0) != pid1);
      while (waitpid(pid2, &status2, 0) != pid2);
      printf("status1=0x%x\n", status1);
      printf("status2=0x%x\n", status2);
      printf("End of clone test.\n");
  }

  int main(int argc, char **argv)
  {
      test_clone();
      return 0;
  }
  Posts: 210
  Joined: 04 Sep 2011 17:43

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