[Bug 240989] Linuxulator: futexes can't be shared between 32- and 64-bit applications

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=240989

            Bug ID: 240989
           Summary: Linuxulator: futexes can't be shared between 32- and
                    64-bit applications
           Product: Base System
           Version: 12.0-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: bugs at FreeBSD.org
          Reporter: iwtcex at gmail.com

Here's a small example:

#define _GNU_SOURCE

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>

#include <sys/syscall.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/mman.h>

#include <linux/futex.h>

#define SHM_FILE_PATH "/futex-bug"

int main() {

  int fd = shm_open(SHM_FILE_PATH, O_CREAT | O_RDWR, 0777);
  assert(fd != -1);

  ftruncate(fd, 4);

  int* addr = mmap(NULL, 4, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  assert(addr != MAP_FAILED);

  close(fd);

#ifdef WAIT

  struct timespec timeout = {.tv_sec = 1, .tv_nsec = 0};
  int err = -1;
  do {
    err = syscall(SYS_futex, addr, FUTEX_WAIT, 0, &timeout, NULL, 0);
    if (err == -1) {
      printf("FUTEX_WAIT: %d [%s]\n", err, strerror(errno));  
    } else {
      printf("FUTEX_WAIT: %d\n", err);
    }
  } while (err == -1 && errno == ETIMEDOUT);

  shm_unlink(SHM_FILE_PATH);

#else

  int err = syscall(SYS_futex, addr, FUTEX_WAKE, 1, NULL, NULL, 0);
  printf("FUTEX_WAKE: %d\n", err);

#endif

  return 0;
}

Compile this with:

/compat/linux/bin/cc -DWAIT -m32 --sysroot=/compat/linux futex_bug.c -lrt -o
wait32
/compat/linux/bin/cc        -m32 --sysroot=/compat/linux futex_bug.c -lrt -o
wake32
/compat/linux/bin/cc        -m64 --sysroot=/compat/linux futex_bug.c -lrt -o
wake64

Run wait32, then try wake64 and wake32.

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