Re: dead-code stripping, pass two...
Re: dead-code stripping, pass two...
- Subject: Re: dead-code stripping, pass two...
- From: Allen Cronce <email@hidden>
- Date: Fri, 19 May 2006 08:03:41 -0700
Hi Steve,
I'd be interested to know is whether or not making any of Andy's changes
made a difference in your executable size. Because like Andy, we went
though the various project options last year to come up with a best
practices set for applications, bundles, etc. It took a ton of research
and experimentation.
Our project options list is a little different than Andy's though,
because found that some of the options added too much work for too
little gain. We ran into a diminishing returns situation where the
changes resulted in too small a size reduction to be meaningful.
We also found odd discrepancies with Apple's docs. For example, going
from default debug symbols to full (which is supposed to be important
for dead code stripping) actually made the post-stripped executable a
little bigger for at least one project.
In any case, with all the "best practices" settings in place, the
project I referenced that was 88k under CW is still a 600k Universal
after stripping symbols. So call it 300k adjusted for a single binary.
That's a 3.4 times size increase under Xcode. If I look at the
pre-stripped binary, it's very clear that stuff that is not needed is
being linked in. In fact, using the disassembly and adding conditionals
was how I got it down from an initial 1.6 meg to 600k.
So I still believe that the linker is at fault here. Because if it's
single pass, and if it operates on an object file level instead of the
function/method level, then no amount of project fiddling is going to
help with certain code situations.
But honestly I have no visibility into what these tools are really
doing. I really wish that Apple would comment on this issue. Because
either we're missing something with all these complex, interrelated
project options, or something is not working with the tools.
Steve, have you thought about making a simple sample that proves that
dead code stripping either works or doesn't? I suspect that if you make
a new project following Andy's recommendations that has an object foo
with an unused method that instances object bar, that the resulting
binary will contain object bar. If dead code stripping *really* worked,
object bar would not be in the binary.
Best,
--
Allen Cronce
Steve Christensen wrote:
> I guess what I'm finding most frustrating is that there doesn't seem
> to be a simple way of doing dead-code stripping. And what I mean by
> that is -all- unused code and data is removed from the output binary.
> Not some of them, a lot of them or most of them.
>
> There seem to be all these magic (for want of a better word)
> combinations of settings that have to be just right or the stripping
> doesn't work correctly. Developers shouldn't have to burden every
> target with a custom script to do what should be either the default
> deployment behavior, or at least one that can be turned -fully- on or
> off with a simple switch.
>
> I guess my question would be, at this point, do you know what the
> compiler and/or linker settings need to be to get the same behavior as
> your script? Or, more correctly, the same thing as a single checkbox
> does in CW?
>
> steve
>
>
> On May 18, 2006, at 9:34 PM, Andy O'Meara wrote:
>
>> Well, that script I referenced ensures that symbol stripping *and* dead
>> stripping are performed. Point being, there's a number of build
>> settings
>> that you need to have set a certain way in order to max out the dead
>> stripping that 'strip' can perform (and many of those settings don't
>> jump
>> out as being directly related to dead-stripping, such as don't make
>> symbols
>> public by default).
>>
>> For example, if you have the flag set that causes unreferenced C++
>> static
>> objects code to not get stripped, lots of stuff can (rightfully) get
>> dragged
>> in as a result. In general, you have to be one with you code to have
>> a feel
>> for what's getting pulled in. If you use 3rd party libraries, it's a
>> lot
>> more risky to enable aggressive stripping (or else stuff will start to
>> break--some devs use unreferenced object and template stuff to do setup
>> stuff). But, I do admit, CW had some very aggressive, yet very
>> smart, dead
>> code stripping that always just worked -- I miss CW like heck.
>>
>> Also, if you're comparing gcc's raw binary size to codewarrior's
>> binary suze
>> as an indicator of how "good" the stripping is, that may not be the best
>> idea. Your best bet may be to disable symbol stripping and then use
>> atos
>> (or search the binary manually using a hex editor) to see if a
>> particular
>> symbol has been stripped or not.
>>
>> Once you get the right linker and compiler flags (depending if you're
>> doing
>> external stripping or not), your gcc binaries won't be much larger
>> than your
>> CW binaries (swag disclaimer: divide the size of a UB by 2). Mine
>> are only
>> about 10-15% larger (my flagship binary under CW was 650k and under
>> Xcode
>> the UB is 1450k).
>>
>> Andy
>>
>>
>> On 5/18/06 12:30 AM, "Steve Christensen" <email@hidden> wrote:
>>
>>> Yes, I'd seen that thread previously. Unless I am mistaken, the
>>> script is used to strip out all the non-public symbols from a binary.
>>> It doesn't appear to actually dead-code strip unused code and data,
>>> which is what the linker is supposed to do.
>>>
>>>
>>> On May 17, 2006, at 8:38 PM, Andy O'Meara wrote:
>>>
>>>> If you search this list archive, you'll find the below thread -- it
>>>> should
>>>> address your questions/problems:
>>>>
>>>> http://lists.apple.com/archives/xcode-users/2006/Mar/msg00552.html
>>>>
>>>>
>>>> On 5/17/06 10:44 PM, "Steve Christensen" <email@hidden> wrote:
>>>>
>>>>> Following another other dead-code stripping thread, I turned on
>>>>> "Symbols hidden by default" (aka [GCC_SYMBOLS_PRIVATE_EXTERN, -
>>>>> fvisibility=hidden]) and noticed a reduction in executable size.
>>>>> However nm is still reporting a lot of API symbols that are only
>>>>> referenced from unused C++ class methods, so I don't know where the
>>>>> reduction actually came from. Thus I'm still kinda in the same boat
>>>>> is before.
>>>>>
>>>>> Any more guesses? :-)
>>>>>
>>>>>
>>>>>
>>>>> On May 17, 2006, at 2:16 PM, Steve Christensen wrote:
>>>>>
>>>>>> On May 17, 2006, at 2:03 PM, Ladd Van Tol wrote:
>>>>>>
>>>>>>> On May 17, 2006, at 11:27 AM, Steve Christensen wrote:
>>>>>>>
>>>>>>>> I'd asked about this last month and didn't really receive any
>>>>>>>> responses, so I figure I should try again just in case.
>>>>>>>>
>>>>>>>> I have a number of plug-in projects I imported from CodeWarrior
>>>>>>>> to Xcode as part of making them Universal and all that. They
>>>>>>>> build and run correctly, but I've noticed that the binary size
>>>>>>>> has grown considerably more than 2x (in one case going from
>>>>>>>> around 48K in CodeWarrior to 197K as a UB built by Xcode).
>>>>>>>>
>>>>>>>> After doing a little more poking around, I found that the problem
>>>>>>>> appears to be that unused class methods are not being stripped
>>>>>>>> out, which means that the method code as well as any that they
>>>>>>>> reference, etc., etc., gets left in the binary. These are not
>>>>>>>> virtual methods, BTW.
>>>>>>>>
>>>>>>>> I have dead-code stripping and symbol stripping turned on, as
>>>>>>>> well as doing an extra post-link strip pass and specifying an
>>>>>>>> exported symbols file just to see if that would make a
>>>>>>>> difference. It doesn't.
>>>>>>>>
>>>>>>>> Is there some magical incantation that I've missed someplace? A
>>>>>>>> known linker bug? A bug in the CodeWarrior project import process?
>>>>>>>
>>>>>>> This is fairly obvious, but do you have -gfull set?
>>>>>>
>>>>>> Yep, or at least that's what the project settings say.
>>> _______________________________________________
>>> Do not post admin requests to the list. They will be ignored.
>>> Xcode-users mailing list (email@hidden)
>>> Help/Unsubscribe/Update your Subscription:
>>>
>>>
>>> This email sent to email@hidden
>>>
>>>
>>
>>
>
> _______________________________________________
> Do not post admin requests to the list. They will be ignored.
> Xcode-users mailing list (email@hidden)
> Help/Unsubscribe/Update your Subscription:
>
>
> This email sent to email@hidden
>
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Xcode-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden