[PATCH v2 5/8] posix: Do not clobber errno by atfork handlers

[Florian Weimer]

* Andreas Schwab:

> On Mär 11 2021, Florian Weimer via Libc-alpha wrote:
>
>> * Adhemerval Zanella via Libc-alpha:
>>
>>> Changes from v1:
>>> * Move the errno set/restore to parent branch.
>>> ---
>>> Checked on x86_64-linux-gnu.
>>> ---
>>>  posix/fork.c | 9 ++++++++-
>>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/posix/fork.c b/posix/fork.c
>>> index cc1bdc1232..a4fdd44e1e 100644
>>> --- a/posix/fork.c
>>> +++ b/posix/fork.c
>>> @@ -68,7 +68,6 @@ __libc_fork (void)
>>>      }
>>>  
>>>    pid_t pid = _Fork ();
>>> -
>>>    if (pid == 0)
>>>      {
>>>        fork_system_setup ();
>>> @@ -99,6 +98,11 @@ __libc_fork (void)
>>>      }
>>>    else
>>>      {
>>> +      /* If _Fork failed, preserve its errno value.  */
>>> +      int save_errno;
>>> +      if (pid < 0)
>>> +	save_errno = errno;
>>> +
>>>        /* Release acquired locks in the multi-threaded case.  */
>>>        if (multiple_threads)
>>>  	{
>>> @@ -111,6 +115,9 @@ __libc_fork (void)
>>>  
>>>        /* Run the handlers registered for the parent.  */
>>>        __run_fork_handlers (atfork_run_parent, multiple_threads);
>>> +
>>> +      if (pid < 0)
>>> +       __set_errno (save_errno);
>>>      }
>>>  
>>>    return pid;
>>
>> This is okay.  GCC does not warn about the uninitialized save_errno
>> here; I checked with build-many-glibcs.py.  Apparently the middle-end is
>> smart enough to detect that the conditions match.
>
> But I think it wouldn't be bad to make that unconditional.

Works for me too.

Thanks,
Florian