Re: debug-early branch merged into mainline

[Richard Biener <richard.guenther@gmail.com>]

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)
and we have only one object block per section name (which it looks like).
Thus can you re-write the compare function to just

  return strcmp (p1->sect->named.name, p2->sect->named.name);

?  (maybe with an assert that SECTION_NAMED is set on both)

Ok with those changes.  Btw, for portability the compare function should
be a total ordering, thus return 0 only iff p1 == p2, otherwise it won't
fix the bug on hosts where qsort may change the order of equal comparing
elements non-deterministically (IIRC Solaris).

Thanks,
Richard.

> Aldy