[Bug driver/18006] New: Please replace vfork() with fork()

[Bug driver/18006] New: Please replace vfork() with fork()

[d dot yu dot bolkhovityanov at inp dot nsk dot su]

When built gcc-4.0 (20041010 snapshot), I discovered that GCC again uses vfork()
instead of regular fork().  This is a "bad thing" due to following reasons:

- vfork() is deprecated -- it was a BSD kludge from old no-MMU-days (a
politically-correct reason :-).

- At least in Linux, vfork()s can't be followed by strace/ltrace, which makes
debugging obscure situations MUCH harder.

Of course, one can say "so -- build your own copy with vfork() disabled" (BTW --
how? There is no "--enable-vfork/--disable-vfork".).

But even having an OPPORTUNITY for vfork() to be used is a danger -- someone
else can supply you a vfork'ed GCC, which is undebuggable.  For example, I've
spent many hours trying to find out why some cross-compiler for PPC fails (it
simply ignored the "-B" switch), while being able to strace it could give the
clue in a minute.

Interestingly, gcc-3.4.2, built in exactly the same way (../gcc-3.4.2/configure
--prefix=/tmp/gcc-3.4 --enable-languages=c,c++) does "the right thing" -- it
uses fork().

-- 
           Summary: Please replace vfork() with fork()
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: driver
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: d dot yu dot bolkhovityanov at inp dot nsk dot su
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18006

[Bug driver/18006] Please replace vfork() with fork()

[schwab at suse dot de]

------- Additional Comments From schwab at suse dot de  2004-10-15 09:32 -------
> - vfork() is deprecated -- it was a BSD kludge from old no-MMU-days (a 
> politically-correct reason :-). 
 
Use of vfork is still a win if you are going to call execve anyway because the 
address space does not need to be copied. 
 
> - At least in Linux, vfork()s can't be followed by strace/ltrace, which makes 
> debugging obscure situations MUCH harder. 
 
This is wrong.  At least strace has no problem following vfork. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18006

[Bug driver/18006] Please replace vfork() with fork()

[d dot yu dot bolkhovityanov at inp dot nsk dot su]

------- Additional Comments From d dot yu dot bolkhovityanov at inp dot nsk dot su  2004-10-15 09:46 -------
> Use of vfork is still a win if you are going to call execve anyway because the
> address space does not need to be copied. 

Yes, it is a tiny win, since vfork() doesn't require copying of page tables, as
opposed to fork().  But address space isn't copied anyway, thanks to
copy-on-write strategy.
 
> > - At least in Linux, vfork()s can't be followed by strace/ltrace, which makes 
> > debugging obscure situations MUCH harder. 
> 
> This is wrong.  At least strace has no problem following vfork. 

>From strace(1) (Fedora Core 2):

"Currently (Linux 2.3.25), strace(1) cannot follow vfork() and  requires a
kernel patch."

That is true at least under 2.4; 2.6 shows somewhat better behaviour.  But there
is a HUGE amount of 2.4 installations, which will remain for long time.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18006

[Bug driver/18006] Please replace vfork() with fork()

[schwab at suse dot de]

------- Additional Comments From schwab at suse dot de  2004-10-15 09:46 -------
> This is wrong.  At least strace has no problem following vfork.  
 
I take that back. My tests were broken. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18006

[Bug driver/18006] Please replace vfork() with fork()

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-10-15 11:55 -------
But who cares that is strace bug which should be fixed because it works on the BSD (and in fact the BSD 
got rid of vfork for a while but now they are adding it back because they found it can faster).
So closing as will not fix.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |WONTFIX


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18006

[Bug driver/18006] Please replace vfork() with fork()

[d dot yu dot bolkhovityanov at inp dot nsk dot su]

------- Additional Comments From d dot yu dot bolkhovityanov at inp dot nsk dot su  2004-10-15 13:02 -------
Andrew, this is not "strace bug", but a vfork() bug that it can't be traced --
strace simply CAN'T do anything to fix it.

If some versions of GCC use fork(), and others -- vfork(), so, GCC in fact
supports both styles, right?  So, can this be made at least configurable?

And as for performance...  Of course, vfork() is slightly faster, but the
performance gain (microseconds?) is neglectable if compared with times spent on
compilation and optimization...


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18006