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Re: [PATCH] Catch exception on solib_svr4_r_ldsomap
- From: Sergio Durigan Junior <sergiodj at redhat dot com>
- To: Pedro Alves <palves at redhat dot com>
- Cc: GDB Patches <gdb-patches at sourceware dot org>
- Date: Tue, 31 Mar 2015 19:39:35 -0400
- Subject: Re: [PATCH] Catch exception on solib_svr4_r_ldsomap
- Authentication-results: sourceware.org; auth=none
- References: <871tke2b6a dot fsf at redhat dot com> <55152B9F dot 4090606 at redhat dot com> <87k2y2qdbu dot fsf_-_ at redhat dot com> <551A8546 dot 4000208 at redhat dot com>
On Tuesday, March 31 2015, Pedro Alves wrote:
>>> So, gdb itself errors and stops processing the core?
>> No, GDB does not "error and stop", but some testcases do that.
> Well, it clearly does do that. Hence your new patch. :-)
>>> I think I don't understand. :-) Can you please show an
>>> example session? Did GDB continue processing the core when
>>> it printed that error, or was it just a warning and it continued?
> I meant "Did GDB stop processing the core", of course.
Sorry I misunderstood your question.
>> Sure, sorry for not sending the example session before! Here is the
>> pertinent part:
>> (gdb) core /home/sergio/work/src/git/binutils-gdb/rhbz1085906-coredump-filter/build-64-3/gdb/testsuite/gdb.base/non-private-anon.gcore
>> [New LWP 28468]
>> Cannot access memory at address 0x355fc21148
>> Cannot access memory at address 0x355fc21140
>> (gdb) FAIL: gdb.base/coredump-filter.exp: loading and testing corefile for non-Private-Anonymous: load core
>> FAIL: gdb.base/coredump-filter.exp: loading and testing corefile
>> for non-Private-Anonymous: loading
>> -nw -nx -data-directory
>> GDB correctly loaded the corefile (despite the warnings), and the
> The error made the rest of core_open be skipped: if the core is still
> loaded, gdb is potentially in an inconsistent state at this point.
> I'd think we should completely discard the core/target if something
> errors out. And then if we can be tolerant to specific parts of
> loading a core failing, we should handle those before the error escapes
> out of core_open. We do something like that
> already (note core_close_cleanup and the TRY/CATCH'S), but it's clearly
> not complete. After:
> push_target (&core_ops);
> discard_cleanups (old_chain);
> ... several things can throw and let an exception escape.
Yeah, certainly we should be catching those before they escape. I will
see if I can take a look at more places to improve/fix later.
>> Right, so I took some time and found the right fix, I think. As we
>> agreed above, the fact that GDB is not printing the "Core was generated
>> by..." message is really strange, so I decided to investigate why it is
>> doing that.
>> The answer is that we are forgetting to check for an exception on
>> solib_svr4_r_ldsomap. When loading the corefile, GDB calls this
>> function, which then calls read_memory_unsigned_integer, which throws an
>> error. This error is not being caught by the function, so it propagates
>> until the main loop catches it. The fix is obvious: we should catch
>> this regression and continue in the function. With it, GDB now
>> correctly prints the "Core was generated by..." message, and the patch
>> to adjust gdb_core_cmd is no longer needed.
>> Regression-tested on Fedora 20 for x86_64, i686 and native-gdbserver.
>> Does that make more sense now?
> Yes, this is OK.
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