Date: Sun, 29 Apr 2012 16:39:12 -0700 From: Marcel Moolenaar <marcel@xcllnt.net> To: Konstantin Belousov <kostikbel@gmail.com> Cc: toolchain@freebsd.org, Dmitry Mikulin <dmitrym@juniper.net> Subject: Re: [GDB follow-fork] behavior change for wait() Message-ID: <1D36CFB0-C4DA-4312-B200-58ABA0937977@xcllnt.net> In-Reply-To: <20120429164300.GR2358@deviant.kiev.zoral.com.ua> References: <7B7A25D1-E99D-486A-B1CA-A5CFEA837B81@xcllnt.net> <20120429164300.GR2358@deviant.kiev.zoral.com.ua>
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On Apr 29, 2012, at 9:43 AM, Konstantin Belousov wrote:
> On Fri, Apr 27, 2012 at 03:33:49PM -0700, Marcel Moolenaar wrote:
>> Hi Dmitry,
>>=20
>> I've been testing the follow-fork changes in GDB and ran into some =
weird
>> behavior. Without gdb, my test program (attached) prints something =
like:
>>=20
>> fbsdvm% ./fe=20
>> fe(41042): initial process. Doing fork & exec...
>> fe(41043): child after fork. Doing exec...
>> fe(41043): child after exec. Exiting...
>> fe(41042): child 41043 exited with status 0
>>=20
>> In particular: the parent (pid=3D41042) calls wait(2) to reap the =
child and
>> the child exits with 0.
>>=20
>> Under gdb, I see this:
>>=20
>> fbsdvm% gdb ./fe
>> GNU gdb 6.1.1 [FreeBSD]
>> Copyright 2004 Free Software Foundation, Inc.
>> GDB is free software, covered by the GNU General Public License, and =
you are
>> welcome to change it and/or distribute copies of it under certain =
conditions.
>> Type "show copying" to see the conditions.
>> There is absolutely no warranty for GDB. Type "show warranty" for =
details.
>> This GDB was configured as "i386-marcel-freebsd"...
>> (gdb) br main
>> Breakpoint 1 at 0x80487b0: file fe.c, line 14.
>> (gdb) run
>> Starting program: /usr/home/marcel/fe=20
>>=20
>> Breakpoint 1, main (argc=3DError accessing memory address 0x1: Bad =
address.
>> ) at fe.c:14
>> 14 {
>> (gdb) n
>> main (argc=3D1, argv=3D0xbfbfebb4) at fe.c:19
>> 19 if (getenv("__FE_FORKED__") !=3D NULL) {
>> (gdb) c
>> Continuing.
>> fe(41141): initial process. Doing fork & exec...
>> [New process 41143]
>> fe(41143): child after fork. Doing exec...
>> fe(41143): child after exec. Exiting...
>> fe(41141): wait(2) failed with error 10 (No child processes)
>>=20
>> Program exited normally.
>> (gdb)=20
>>=20
>> When stepping at least once, the inferior will not be able to =
properly wait(2)
>> for its child as it seems to have been reaped already. I suspect this =
is done
>> by the debugger -- unintentionally at least.
>>=20
>> Have you seen this before?
>=20
> How old is your kernel ? In particular, do you have
> r232048+r232104+r232947+r232975+r233808+r233809 ?
Yup:
fbsdvm% uname -a
FreeBSD fbsdvm 10.0-CURRENT FreeBSD 10.0-CURRENT #6 r234823: Sun Apr 29 =
16:18:07 PDT 2012 marcel@fbsdvm:/usr/obj/usr/src/sys/FBSDVM i386
This is off of the projects/nand branch, BTW:
fbsdvm% svn info
Path: .
Working Copy Root Path: /usr/src
URL: svn+ssh://svn.freebsd.org/base/projects/nand
Repository Root: svn+ssh://svn.freebsd.org/base
Repository UUID: ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Revision: 234823
Node Kind: directory
Schedule: normal
Last Changed Author: gber
Last Changed Rev: 234550
Last Changed Date: 2012-04-21 10:48:17 -0700 (Sat, 21 Apr 2012)
Which is sync'd up to head @234446.
--=20
Marcel Moolenaar
marcel@xcllnt.net
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