Re: debug-early branch merged into mainline

[Aldy Hernandez <aldyh@redhat.com>]

On 06/08/2015 09:30 AM, Richard Biener wrote:
> On Mon, Jun 8, 2015 at 2:05 PM, Aldy Hernandez <aldyh@redhat.com> wrote:
>> On 06/08/2015 04:26 AM, Richard Biener wrote:
>>>
>>> On Mon, Jun 8, 2015 at 3:23 AM, Aldy Hernandez <aldyh@redhat.com> wrote:
>>>>
>>>> On 06/07/2015 02:33 PM, Richard Biener wrote:
>>>>>
>>>>>
>>>>> On June 7, 2015 6:00:05 PM GMT+02:00, Aldy Hernandez <aldyh@redhat.com>
>>>>> wrote:
>>>>>>
>>>>>>
>>>>>> On 06/07/2015 11:25 AM, Richard Biener wrote:
>>>>>>>
>>>>>>>
>>>>>>> On June 7, 2015 5:03:30 PM GMT+02:00, Aldy Hernandez
>>>>>>
>>>>>>
>>>>>> <aldyh@redhat.com> wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On 06/06/2015 05:49 AM, Andreas Schwab wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Bootstrap fails on aarch64:
>>>>>>>>>
>>>>>>>>> Comparing stages 2 and 3
>>>>>>>>> warning: gcc/cc1objplus-checksum.o differs
>>>>>>>>> warning: gcc/cc1obj-checksum.o differs
>>>>>>>>> warning: gcc/cc1plus-checksum.o differs
>>>>>>>>> warning: gcc/cc1-checksum.o differs
>>>>>>>>> Bootstrap comparison failure!
>>>>>>>>> gcc/ira-costs.o differs
>>>>>>>>> gcc/tree-sra.o differs
>>>>>>>>> gcc/tree-parloops.o differs
>>>>>>>>> gcc/tree-vect-data-refs.o differs
>>>>>>>>> gcc/java/jcf-io.o differs
>>>>>>>>> gcc/ipa-inline-analysis.o differs
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> The bootstrap comparison failure on ppc64le, aarch64, and possibly
>>>>>>>> others is due to the order of some sections being in a different
>>>>>>
>>>>>>
>>>>>> order
>>>>>>>>
>>>>>>>>
>>>>>>>> with and without debugging.
>>>>>>>>
>>>>>>>> Stage2 is being compiled with no debugging due to -gtoggle, and
>>>>>>
>>>>>>
>>>>>> stage3
>>>>>>>>
>>>>>>>>
>>>>>>>> is being compiled with debugging.
>>>>>>>>
>>>>>>>> For ira-costs.o on ppc64le we have:
>>>>>>>>
>>>>>>>> -Disassembly of section
>>>>>>>>
>>>>>>
>>>>>>
>>>>>> .rodata._ZN10hash_tableI19cost_classes_hasher11xcallocatorE6expandEv.str1.8:
>>>>>>>>
>>>>>>>>
>>>>>>>> +Disassembly of section
>>>>>>>>
>>>>>>
>>>>>>
>>>>>> .rodata._ZN10hash_tableI19cost_classes_hasher11xcallocatorE26find_empty_slot_for_expandEj.str1.8:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> ...
>>>>>>>>
>>>>>>>> -Disassembly of section
>>>>>>>>
>>>>>>
>>>>>>
>>>>>> .rodata._ZN10hash_tableI19cost_classes_hasher11xcallocatorE26find_empty_slot_for_expandEj.str1.8:
>>>>>>>>
>>>>>>>>
>>>>>>>> +Disassembly of section
>>>>>>>>
>>>>>>
>>>>>>
>>>>>> .rodata._ZN10hash_tableI19cost_classes_hasher11xcallocatorE6expandEv.str1.8:
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> There is no semantic difference between the objects, just the
>>>>>>
>>>>>>
>>>>>> ordering.
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> I assume it's the same problem for the rest of the objects and
>>>>>>>> architectures.
>>>>>>>>
>>>>>>>> I will look into this, unless someone beats me to it, or has an idea
>>>>>>>> right off the bat.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> Check whether the symbol table walkers are walking hash tables.  I
>>>>>>
>>>>>>
>>>>>> assume the above are emitted via the symbol removal handling for debug
>>>>>> stuff?
>>>>>>
>>>>>> Ughh, indeed.  These sections are being outputted from
>>>>>> output_object_blocks which traverses a hash table:
>>>>>>
>>>>>> void
>>>>>> output_object_blocks (void)
>>>>>> {
>>>>>>     object_block_htab->traverse<void *, output_object_block_htab>
>>>>>> (NULL);
>>>>>> }
>>>>>>
>>>>>> Perhaps we should sort them by some deterministic field and then call
>>>>>> output_object_block() on each member of the resulting list?
>>>>>
>>>>>
>>>>>
>>>>> Yes, that would be the usual fix. Maybe sth has an UID already, is the
>>>>> 'object' a decl by chance?
>>>>
>>>>
>>>>
>>>> The attached patch fixes the bootstrap failure on ppc64le, and
>>>> theoretically
>>>> the aarch64 problem as well, but I haven't checked.
>>>>
>>>> Tested on ppc64le linux by bootstrapping, and regtesting C/C++ against
>>>> pre
>>>> debug-early merge sources.  Also tested by a full bootstrap and regtest
>>>> on
>>>> x86-64 Linux.
>>>>
>>>> OK for mainline?
>>>
>>>
>>> Please use FOR_EACH_HASH_TABLE_ELEMENT to put elements on the
>>> vector instead of the htab traversal.
>>>
>>> The compare function looks like we will end up having many equal elements
>>> (and thus random ordering on hosts where qsort doesn't behave "sane"
>>> here, like Solaris IIRC).  Unless all sections are named (which it looks
>>> like)
>>
>>
>> Some sections are not named.
>>
>> How about we sort the named sections and output them, but call
>> output_object_block() on the rest of the sections on whatever order they
>> were in?  This solves the bootstrap problem as well.
>>
>> Attached patch tested on x86-64 and ppc64le Linux.
>>
>> OK?
>
> No, but hash_section suggests to sort after sect->common.flags if
> the section is not named.  Conveniently flags is just an 'int' ...

What about if the comparison routine gets a named section and an unnamed 
section?  How to compare?  That's why I was giving priority to one over 
the other originally, but I didn't know about problematic qsort 
implementations.

Aldy