[GDB follow-fork] behavior change for wait()

[Konstantin Belousov]

On Fri, Apr 27, 2012 at 03:33:49PM -0700, Marcel Moolenaar wrote:
> Hi Dmitry,
> 
> 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:
> 
> fbsdvm%	./fe 
> 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
> 
> In particular: the parent (pid=41042) calls wait(2) to reap the child and
> the child exits with 0.
> 
> Under gdb, I see this:
> 
> 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 
> 
> Breakpoint 1, main (argc=Error accessing memory address 0x1: Bad address.
> ) at fe.c:14
> 14	{
> (gdb) n
> main (argc=1, argv=0xbfbfebb4) at fe.c:19
> 19		if (getenv("__FE_FORKED__") != 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)
> 
> Program exited normally.
> (gdb) 
> 
> 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.
> 
> Have you seen this before?

How old is your kernel ? In particular, do you have
r232048+r232104+r232947+r232975+r233808+r233809 ?

I cannot reproduce your issue on recent kernels and patched gdb.
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