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Date:      Tue, 01 Oct 2019 23:44:31 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 240989] Linuxulator: futexes can't be shared between 32- and 64-bit applications
Message-ID:  <bug-240989-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D240989

            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@FreeBSD.org
          Reporter: iwtcex@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 =3D shm_open(SHM_FILE_PATH, O_CREAT | O_RDWR, 0777);
  assert(fd !=3D -1);

  ftruncate(fd, 4);

  int* addr =3D mmap(NULL, 4, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  assert(addr !=3D MAP_FAILED);

  close(fd);

#ifdef WAIT

  struct timespec timeout =3D {.tv_sec =3D 1, .tv_nsec =3D 0};
  int err =3D -1;
  do {
    err =3D syscall(SYS_futex, addr, FUTEX_WAIT, 0, &timeout, NULL, 0);
    if (err =3D=3D -1) {
      printf("FUTEX_WAIT: %d [%s]\n", err, strerror(errno));=20=20
    } else {
      printf("FUTEX_WAIT: %d\n", err);
    }
  } while (err =3D=3D -1 && errno =3D=3D ETIMEDOUT);

  shm_unlink(SHM_FILE_PATH);

#else

  int err =3D 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=3D/compat/linux futex_bug.c -lrt=
 -o
wait32
/compat/linux/bin/cc        -m32 --sysroot=3D/compat/linux futex_bug.c -lrt=
 -o
wake32
/compat/linux/bin/cc        -m64 --sysroot=3D/compat/linux futex_bug.c -lrt=
 -o
wake64

Run wait32, then try wake64 and wake32.

--=20
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