Re: expected behavior when a signal is sent to the ptraced child

[Wu Zhou <woodzltc@cn.ibm.com>]

On Thu, 25 May 2006, Daniel Jacobowitz wrote:

> On Thu, May 25, 2006 at 11:06:43AM +0200, Andreas Schwab wrote:
> > Wu Zhou <woodzltc@cn.ibm.com> writes:
> > 
> > > What I expect is the parent will at least output:
> > >
> > > stopped by signal 5 
> > >
> > > What is the  problem here?  Did I make something wrong?
> > 
> > You need to use waitpid/wait4 and add WUNTRACED to the options parameter.
> > Without that you'll never receive notification of stopped processes.
> 
> WUNTRACED shouldn't be necessary in this case because the child is
> actually ptraced.

I guess Daniel is right.  the manual of wait/waitpid says this about 
WUNTRACED:
  also  return if  a  child  has  stopped  (but  not  traced  via
  ptrace).  Status for traced children which  have  stopped  is
  provided even if this option is not specified.

In the testcase, I use PTRACE_ATTACH to trace the child. So WUNTRACED is 
not needed here.  

Thank you anyway!  At least I learned that there is a WUNTRACED option 
to change the behavior of the delivery of a signal. it lets the child 
stop without tracing it.  A good feature indeed, right?

Regards
- Wu Zhou

P.S: it seems that my mail agent have some problems when connecting from 
home. It sent a couple repeated message.  Sorry for that!