Re: [Qemu-devel] [PATCH v2 1.3] build: compile translate.o with -fno-gcse option

[Wenchao Xia <xiawenc@linux.vnet.ibm.com>]

于 2012-11-28 10:01, 陳韋任 (Wei-Ren Chen) 写道:
> On Tue, Nov 27, 2012 at 05:21:03PM +0100, Paolo Bonzini wrote:
>> Some versions of GCC require insane (>2GB) amounts of memory to compile
>> translate.o.  As a countermeasure, disable the culprit optimization pass.
>> This should fix the buildbot failure for default_x86_64_fedora16.
>> Anyway is a good thing to do because people will try to compile 1.3 with
>> less than 2GB of memory and complain.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>>   Makefile.target | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/Makefile.target b/Makefile.target
>> index 8b658c0..d38bb58 100644
>> --- a/Makefile.target
>> +++ b/Makefile.target
>> @@ -143,6 +143,12 @@ GENERATED_HEADERS += hmp-commands.h qmp-commands-old.h
>>
>>   endif # CONFIG_SOFTMMU
>>
>> +# Workaround for http://gcc.gnu.org/PR55489.  Happens with -fPIE/-fPIC
>> +# and large functions that use global variables.  The bug is in all
>> +# releases of GCC, but it became particularly acute in 4.7.x.  We
>> +# should be able to delete this at the end of 2013.
>> +%/translate.o: QEMU_CFLAGS += -fno-gcse
>> +
>>   nested-vars += obj-y
>>
>>   # This resolves all nested paths, so it must come last
>
>    No objection here. But will we remove this option when GCC fix this pr
> or we just leave it there? If we're going to remove it in the future,
> better keep a note on the release change log or somewhere else.
>
> Regards,
> chenwj
>
   +1, I think -fno-gcse is good enough to fix the problem quickly,
and a note would be nice which remind people that translate.o was
compiled with special flag now. If some one find it problem with
special compiler, or some thing about performance, he can find the
reason quickly.


-- 
Best Regards

Wenchao Xia