Re: [Qemu-devel] [PATCH 10/33] linux-user: Split out brk, close, exit, read, write

[Richard Henderson]

On 06/04/2018 01:17 PM, Laurent Vivier wrote:
> Le 01/06/2018 à 09:30, Richard Henderson a écrit :
>> These are relatively simple unconditionally defined syscalls.
>>
>> Signed-off-by: Richard Henderson <address@hidden>
>> ---
>>  linux-user/syscall.c | 198 ++++++++++++++++++++++++-------------------
>>  1 file changed, 111 insertions(+), 87 deletions(-)
>>
>> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
>> index fc3dc3f40d..b0d268dab7 100644
>> --- a/linux-user/syscall.c
>> +++ b/linux-user/syscall.c
>> @@ -7984,6 +7984,112 @@ IMPL(enosys)
>>      return do_unimplemented(num);
>>  }
>>  
>> +IMPL(brk)
>> +{
>> +    return do_brk(arg1);
>> +}
>> +
>> +IMPL(close)
>> +{
>> +    if (is_hostfd(arg1)) {
>> +        return -TARGET_EBADF;
>> +    }
>> +    fd_trans_unregister(arg1);
>> +    return get_errno(close(arg1));
>> +}
>> +
>> +IMPL(exit)
>> +{
>> +    CPUState *cpu = ENV_GET_CPU(cpu_env);
>> +
>> +    /* In old applications this may be used to implement _exit(2).
>> +       However in threaded applictions it is used for thread termination,
>> +       and _exit_group is used for application termination.
>> +       Do thread termination if we have more then one thread.  */
>> +    if (block_signals()) {
>> +        return -TARGET_ERESTARTSYS;
>> +    }
>> +
>> +    cpu_list_lock();
>> +
>> +    if (CPU_NEXT(first_cpu)) {
>> +        /* Remove the CPU from the list.  */
>> +        QTAILQ_REMOVE(&cpus, cpu, node);
>> +        cpu_list_unlock();
>> +
>> +        TaskState *ts = cpu->opaque;
>> +        if (ts->child_tidptr) {
>> +            put_user_u32(0, ts->child_tidptr);
>> +            sys_futex(g2h(ts->child_tidptr), FUTEX_WAKE, INT_MAX,
>> +                      NULL, NULL, 0);
>> +        }
>> +        thread_cpu = NULL;
>> +        object_unref(OBJECT(cpu));
>> +        g_free(ts);
>> +        rcu_unregister_thread();
>> +        pthread_exit(NULL);
>> +    } else {
>> +        cpu_list_unlock();
>> +
>> +#ifdef TARGET_GPROF
>> +        _mcleanup();
>> +#endif
>> +        gdb_exit(cpu_env, arg1);
>> +        _exit(arg1);
>> +    }
>> +    g_assert_not_reached();
>> +}
>> +
>> +IMPL(read)
>> +{
>> +    abi_long ret;
>> +    char *fn;
>> +
>> +    if (arg3 == 0) {
>> +        return 0;
>> +    }
>> +    if (is_hostfd(arg1)) {
>> +        return -TARGET_EBADF;
>> +    }
>> +    fn = lock_user(VERIFY_WRITE, arg2, arg3, 0);
>> +    if (!fn) {
>> +        return -TARGET_EFAULT;
>> +    }
>> +    ret = get_errno(safe_read(arg1, fn, arg3));
>> +    if (ret >= 0 && fd_trans_host_to_target_data(arg1)) {
>> +        ret = fd_trans_host_to_target_data(arg1)(fn, ret);
>> +    }
>> +    unlock_user(fn, arg2, ret);
>> +    return ret;
>> +}
>> +
>> +IMPL(write)
>> +{
>> +    abi_long ret;
>> +    char *fn;
>> +
>> +    if (is_hostfd(arg1)) {
>> +        return -TARGET_EBADF;
>> +    }
>> +    fn = lock_user(VERIFY_READ, arg2, arg3, 1);
>> +    if (!fn) {
>> +        return -TARGET_EFAULT;
>> +    }
>> +    if (fd_trans_target_to_host_data(arg1)) {
>> +        void *copy = g_malloc(arg3);
>> +        memcpy(copy, fn, arg3);
>> +        ret = fd_trans_target_to_host_data(arg1)(copy, arg3);
>> +        if (ret >= 0) {
>> +            ret = get_errno(safe_write(arg1, copy, ret));
>> +        }
>> +        g_free(copy);
>> +    } else {
>> +        ret = get_errno(safe_write(arg1, fn, arg3));
>> +    }
>> +    unlock_user(fn, arg2, ret);
>> +    return ret;
>> +}
>> +
>>  /* This is an internal helper for do_syscall so that it is easier
>>   * to have a single return point, so that actions, such as logging
>>   * of syscall results, can be performed.
>> @@ -7999,83 +8105,6 @@ IMPL(everything_else)
>>      char *fn;
>>  
>>      switch(num) {
>> -    case TARGET_NR_exit:
>> -        /* In old applications this may be used to implement _exit(2).
>> -           However in threaded applictions it is used for thread 
>> termination,
>> -           and _exit_group is used for application termination.
>> -           Do thread termination if we have more then one thread.  */
>> -
>> -        if (block_signals()) {
>> -            return -TARGET_ERESTARTSYS;
>> -        }
>> -
>> -        cpu_list_lock();
>> -
>> -        if (CPU_NEXT(first_cpu)) {
>> -            TaskState *ts;
>> -
>> -            /* Remove the CPU from the list.  */
>> -            QTAILQ_REMOVE(&cpus, cpu, node);
>> -
>> -            cpu_list_unlock();
>> -
>> -            ts = cpu->opaque;
>> -            if (ts->child_tidptr) {
>> -                put_user_u32(0, ts->child_tidptr);
>> -                sys_futex(g2h(ts->child_tidptr), FUTEX_WAKE, INT_MAX,
>> -                          NULL, NULL, 0);
>> -            }
>> -            thread_cpu = NULL;
>> -            object_unref(OBJECT(cpu));
>> -            g_free(ts);
>> -            rcu_unregister_thread();
>> -            pthread_exit(NULL);
>> -        }
>> -
>> -        cpu_list_unlock();
>> -#ifdef TARGET_GPROF
>> -        _mcleanup();
>> -#endif
>> -        gdb_exit(cpu_env, arg1);
>> -        _exit(arg1);
>> -        return 0; /* avoid warning */
>> -    case TARGET_NR_read:
>> -        if (arg3 == 0) {
>> -            return 0;
>> -        } else {
>> -            if (is_hostfd(arg1)) {
>> -                return -TARGET_EBADF;
>> -            }
>> -            if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0)))
>> -                return -TARGET_EFAULT;
>> -            ret = get_errno(safe_read(arg1, p, arg3));
>> -            if (ret >= 0 &&
>> -                fd_trans_host_to_target_data(arg1)) {
>> -                ret = fd_trans_host_to_target_data(arg1)(p, ret);
>> -            }
>> -            unlock_user(p, arg2, ret);
>> -        }
>> -        return ret;
>> -    case TARGET_NR_write:
>> -        if (is_hostfd(arg1)) {
>> -            return -TARGET_EBADF;
>> -        }
>> -        if (!(p = lock_user(VERIFY_READ, arg2, arg3, 1)))
>> -            return -TARGET_EFAULT;
>> -        if (fd_trans_target_to_host_data(arg1)) {
>> -            void *copy = g_malloc(arg3);
>> -            memcpy(copy, p, arg3);
>> -            ret = fd_trans_target_to_host_data(arg1)(copy, arg3);
>> -            if (ret >= 0) {
>> -                ret = get_errno(safe_write(arg1, copy, ret));
>> -            }
>> -            g_free(copy);
>> -        } else {
>> -            ret = get_errno(safe_write(arg1, p, arg3));
>> -        }
>> -        unlock_user(p, arg2, 0);
>> -        return ret;
>> -
>>  #ifdef TARGET_NR_open
>>      case TARGET_NR_open:
>>          if (!(p = lock_user_string(arg1)))
>> @@ -8116,15 +8145,6 @@ IMPL(everything_else)
>>          fd_trans_unregister(ret);
>>          return ret;
>>  #endif
>> -    case TARGET_NR_close:
>> -        if (is_hostfd(arg1)) {
>> -            return -TARGET_EBADF;
>> -        }
>> -        fd_trans_unregister(arg1);
>> -        return get_errno(close(arg1));
>> -
>> -    case TARGET_NR_brk:
>> -        return do_brk(arg1);
>>  #ifdef TARGET_NR_fork
>>      case TARGET_NR_fork:
>>          return get_errno(do_fork(cpu_env, TARGET_SIGCHLD, 0, 0, 0, 0));
>> @@ -12894,7 +12914,11 @@ IMPL(everything_else)
>>  }
>>  
>>  static impl_fn * const syscall_table[] = {
>> -    impl_everything_else,
>> +    [TARGET_NR_brk] = impl_brk,
>> +    [TARGET_NR_close] = impl_close,
>> +    [TARGET_NR_exit] = impl_exit,
>> +    [TARGET_NR_read] = impl_read,
>> +    [TARGET_NR_write] = impl_write,
>>  };
>>  
>>  abi_long do_syscall(void *cpu_env, unsigned num, abi_long arg1,
>>
> 
> Starting with this patch, this is broken...
> 
> For instance with ppc64le target:
> 
> qemu: Unsupported syscall: 33
> qemu: Unsupported syscall: 33
> qemu: Unsupported syscall: 5
> qemu: Unsupported syscall: 5
> qemu: Unsupported syscall: 5
> qemu: Unsupported syscall: 5
> qemu: Unsupported syscall: 5
> qemu: Unsupported syscall: 5
> qemu: Unsupported syscall: 5
> qemu: Unsupported syscall: 5
> qemu: Unsupported syscall: 5
> /bin/uname: error while loading shared libraries: libc.so.6: cannot open
> shared object file: Error 38
> 
> for instance, for num = TARGET_NR_OPEN:
> 
> +    impl_fn *fn = impl_everything_else;
> 
> -> fn = impl_everything_else
> 
> +    if (num < ARRAY_SIZE(syscall_table)) {
> +        fn = syscall_table[num];
> 
> -> fn = NULL
> 
> +    }
> +    if (fn == NULL) {
> +        fn = impl_enosys;
> 
> -> fn = impl_enosys;
> 
> +    }
> 
> So all undefined syscall numbers < max(defined syscall numbers) will
> call impl_enosys.
> 
> You should do
> 
>     fn = NULL;
>     if (num < ARRAY_SIZE(syscall_table)) {
>         fn = syscall_table[num];
>     }
>     if (fn == NULL) {
>         fn = impl_eveything_else;
>     }
> 
> and the impl_enosys is managed by impl_eveything_else.
> 
> You can come back to your initial code when all syscalls are split out
> (when you remove the enosys case from everything_else)... otherwise we
> will not be able to bisect this part in the future.

Ack.  How did my testing not catch this.  Will fix.


r~