Re: Frysk minutes 20060905

[Alexandre Oliva <aoliva at redhat dot com>]

On Sep  6, 2006, Andrew Cagney <cagney@redhat.com> wrote:

> Wu Zhou wrote:
>> 
>>> libunwind: please test Alex patches. Andrew: to review. We can start
>>> plug it into the sourcewindow, in the space reserved for it already.
>>> The patches from Alex are not checked in yet. Please review and check
>>> in asap.
>> 
>> We had a test.  TestStackBacktrace works ok with this patch applied.
>> But we have a concern that frysk-sys are using some synchronization
>> mechanism to handle ptrace requests.  This patch use ptrace
>> directly.  Is it possible some synchroinization problem might be
>> introduced in?
>> 
> Wu, good catch.  Yes, the backtrace code cannot call ptrace directory;
> it will not work.  All ptrace calls must be routed through the ptrace
> thread that Mike added.

Just for the record (I hadn't read this before, and I'm not sure I've
already clarified it), nothing in the backtrace code calls ptrace
directly.  We're only using part of the libunwind-ptrace interface,
and that's the part that interfaces with files et al.  All of the
callbacks that actually issue ptrace calls are implemented entirely in
frysk, so even when the libunwind-ptrace callbacks need to read
registers or memory from remote processes, they go through frysk's
callbacks to do so, getting correct synchronization.

-- 
Alexandre Oliva         http://www.lsd.ic.unicamp.br/~oliva/
Secretary for FSF Latin America        http://www.fsfla.org/
Red Hat Compiler Engineer   aoliva@{redhat.com, gcc.gnu.org}
Free Software Evangelist  oliva@{lsd.ic.unicamp.br, gnu.org}