svn commit: r270444 - in head/sys: kern sys
John-Mark Gurney
jmg at funkthat.com
Tue Aug 26 19:32:18 UTC 2014
John Baldwin wrote this message on Tue, Aug 26, 2014 at 15:09 -0400:
> On Monday, August 25, 2014 6:30:34 pm John-Mark Gurney wrote:
> > John Baldwin wrote this message on Mon, Aug 25, 2014 at 13:35 -0400:
> > > On Monday, August 25, 2014 07:02:41 PM Mateusz Guzik wrote:
> > > > On Mon, Aug 25, 2014 at 10:23:19AM -0400, John Baldwin wrote:
> > > > > On Sunday, August 24, 2014 09:04:09 AM Mateusz Guzik wrote:
> > > > > > Author: mjg
> > > > > > Date: Sun Aug 24 09:04:09 2014
> > > > > > New Revision: 270444
> > > > > > URL: http://svnweb.freebsd.org/changeset/base/270444
> > > > > >
> > > > > > Log:
> > > > > > Fix getppid for traced processes.
> > > > > >
> > > > > > Traced processes always have the tracer set as the parent.
> > > > > > Utilize proc_realparent to obtain the right process when needed.
> > > > >
> > > > > Are you sure this won't break things? I know of several applications that
> > > > > expect a debugger to be the parent when attached and change behavior as a
> > > > > result (e.g. inserting a breakpoint on an assertion failure rather than
> > > > > generating a core).
> > > >
> > > > Well, this is what linux and solaris do.
> > >
> > > Interesting.
> > >
> > > > I don't feel strongly about this change. If you really want I'm happy to
> > > > revert.
> > >
> > > In general I'd like to someday have the debugger-debuggee relationship not
> > > override parent-child and this is a step in that direction. However, this
> > > will break existing applications, so this needs to be clearly documented in
> > > the release notes. In addition, we should probably advertise how a process
> > > can correctly determine if it is being run under a debugger (right now you can
> > > do 'getppid()' and use strcmp or strstr on the p_comm of that pid so you can
> > > do different things for "gdb" vs "gcore", etc. so just checking P_TRACED from
> > > kinfo_proc wouldn't be equivalent in functionality)
> >
> > But what about when you attach gdb to a running process... That
> > doesn't magicly make the now debugged process a child of gdb does it?
>
> % cat hello.c
> #include <stdio.h>
>
> int
> main()
> {
> printf("hello world\n");
> (void)getchar();
> return (0);
> }
> % cc -g hello.c -o hello
> % ./hello
> hello world
> load: 9.81 cmd: hello 42599 [ttyin] 1.67r 0.00u 0.00s 0% 1056k
>
> < different window >
>
> % ps -O ppid -p `pgrep hello`
> PID PPID TT STAT TIME COMMAND
> 42599 5340 16 I+ 0:00.00 ./hello
> % gdb hello `pgrep hello`
> GNU gdb 6.1.1 [FreeBSD]
> ...
> (gdb) <hit Ctrl-Z>
> Suspended
> % ps -O ppid -p `pgrep hello`
> PID PPID TT STAT TIME COMMAND
> 42599 45079 16 TX+ 0:00.00 ./hello
Wow, learn something new every day...
But doesn't that break apps that use getppid to signal their parent
that forked them?
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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