Re: [PATCH] Fix PR 21337 v2: segfault when re-reading symbols with remote debugging.

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2017-04-29 13:12, Doug Gilmore wrote:
> On 04/28/17 18:41, Simon Marchi wrote:
>> On 2017-04-28 19:44, Doug Gilmore wrote:
>>> Hi Simon,
>>> 
>>> After thinking about it my comment and code placement wasn't
>>> particularly good.  Something along the line's of Luis's change
>>> is better.
>>> 
>>> Does Luis's comment address the question you have?
>>> 
>>> If so, Luis: Should is it OK we incorporate your changes in the 
>>> patch?
>>> 
>>> I attached a diff for the change.
>>> 
>>> Thanks,
>>> 
>>> Doug
>> 
>> Hi Doug,
>> 
>> The comment certainly helps, but in the commit log I'd like to see a
>> more detailed list of events that leads to the crash.
>> 
>> Now that I look into it again, I think I understand.  The
>> objfile_pspace_info::sections array/vector is a list of obj_section
>> pointers (in C++ we'd probably use an std::vector<obj_section*>).
>> That list contains pointers to all the sections from all the
>> objfiles sorted in order of increasing address.  They point directly
>> to the sections allocated by the objfile in their obstacks (and
>> accessible through objfile::sections).  So when the obstack is freed
>> in reread_symbols, the sorted list contains stale pointers.  Is that
>> it?
> Right.
>> 
>> If that's what's happening, then I'm more convinced the fix is
>> right.  Is this behaviour caught by a test?  If not, could you write
>> one?
>> ...
> I'll need to take a look.  Last time I tried I it was more difficult
> to expose the problem on the native build of GDB.

reread_symbols is called when using the run (run_command_1), attach 
(attach_post_wait which then calls setup_inferior) and load 
(load_command) commands.  So maybe something like this would reproduce 
it?

- compile test program
- launch gdb with test program
- touch test program
- run

Simon