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Re: PATCH: Turn on -fomit-frame-pointer by default for 32bit Linux/x86


On 08/04/2010 05:08 PM, H.J. Lu wrote:
> On Wed, Aug 4, 2010 at 7:59 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
>>> Andrew Haley wrote:
>>>
>>>>> On balance, I think it's appropriate to make the change.  I think
>>>>> there's an overall move towards ABIs without frame pointers, and
>>>>> that if x86 stakeholders want to change, it's not our place as GCC
>>>>> maintainers to do this.
>>>
>>>> A problem with "x86 stakeholders" is that we've historically been
>>>> rather poor at finding our users and consulting them before making
>>>> changes.  This has resulted in a number of flamewars, particularly
>>>> over type-based alias analysis.
>>>
>>> That's a general problem with free software: there are zillions of
>>> users, and we don't know where they are or what they want.  I don't
>>> think there's a really great way to solve this problem, though there's
>>> no doubt an interesting Ph.D. thesis in there somewhere.
>>>
>>> One thing we could do pretty easily is to ask some distributions whether
>>> they will accept the change in defaults -- or undo it locally.  If, for
>>> example, Red Hat product management is going to tweak the compiler so
>>> that it's default is -fno-omit-frame-pointer, in order to maintain
>>> backwards compatibility, then that's a valuable data point, since it
>>> means that Red Hat believes its customers would be unhappy with the
>>> change.  On the other hand, if Debian says that they'll happily go along
>>> with the change, then that's a point in favor of making the change.
>>>
>>> So, maybe we need a poll of some of the most popular x86 Linux
>>> distributions, such as Debian, Red Hat, SuSe, and Ubuntu?
>>
>> I went through the defualt changing discussion at a time we was introducing
>> x86-64 port.
>> In general, I believe -fomit-frame-pointer by default is win. x86-64
>> defaults to this for a while and thus the pain of switching should be limited,
>> since most of packages adopted to 64bit world.
>>
>> Probably the most touchy issue concerning the switch is place where you need
>> stack unwinding fast.  This is the case of oprofile and some of garbage collector
>> implementations.
>>
> 
> Can we find if oprofile works with -fomit-frame-pointer on 32bit Linux/x86.

I'll ask.

> As for "some garbage collector implementations", do they work on
> Linux/x86-64? Do they work with icc on 32bit Linux/x86?
> 


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