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Re: [PATCH] Catch exception on solib_svr4_r_ldsomap

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
>> /home/sergio/work/src/git/binutils-gdb/rhbz1085906-coredump-filter/build-64-3/gdb/testsuite/gdb.base/non-private-anon.gcore
>>   spawn
>> /home/sergio/work/src/git/binutils-gdb/rhbz1085906-coredump-filter/build-64-3/gdb/testsuite/../../gdb/gdb
>> -nw -nx -data-directory
>> /home/sergio/work/src/git/binutils-gdb/rhbz1085906-coredump-filter/build-64-3/gdb/testsuite/../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.

Thanks, pushed:


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