[llvm-dev] objc object file generated for gnustep runtime for ELF target is too big

[Perevalov Alexey via llvm-dev]

От: mehdi.amini at apple.com <mehdi.amini at apple.com> от имени Mehdi Amini <mehdi.amini at apple.com>
Отправлено: 27 сентября 2016 г. 8:46
Кому: Perevalov Alexey
Копия: cfe-users at lists.llvm.org; llvm-dev at lists.llvm.org
Тема: Re: [llvm-dev] objc object file generated for gnustep runtime for ELF target is too big
    

> On Sep 26, 2016, at 6:33 AM, Perevalov Alexey via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Dear community,
> 
> 
> I'm using gnustep runtime -fobjc-runtime=gnustep with       gnustep-libobjc2 (https://github.com/gnustep/libobjc2) and
> 
> Cocotron/Chameleon.
> 
> For following source file
> 
> #import <Foundation/Foundation.h>
>      #import <UIKit/UIKit.h>
> 
> int main(void)
>        {
>                NSString *str = [NSString stringWithCString:"TEST"];
>                NSLog(@"test object %@", str);
>                return 0;
>        }
> 
> Compilation in xcode's clang

>Which version?

I think, it doesn't matter, due to with xcode's clang all fine

but if you intersting,

xcrun -sdk iphoneos clang --version
Apple LLVM version 7.0.0 (clang-700.1.76)
Target: x86_64-apple-darwin15.0.0
Thread model: posix

also all fine with open source llvm clang if I choose ios as -fobjc-runtime, I got troubles only with gnustep runtime in clang+llvm-3.8.0 and 3.9.x.

>— 
>Mehdi


> xcrun -sdk iphoneos clang -arch armv7s -mios-version-min=6.1 -c       test_foundation.m -o test_foundation_apple.o
> gives following result:
> 1. object file has only 3156 bytes size
> 2. and in disassembler only main function
> 3. the final executable will be 49992 bytes size in this case
> 
> 
> But compilation in llvm's clang downloaded from  http://llvm.org/releases/3.8.0/clang+llvm-3.8.0-x86_64-apple-darwin.tar.xz
> 
> (
> clang version 3.8.0 (tags/RELEASE_380/final)
>      Target: x86_64-apple-darwin15.0.0
>      Thread model: posix
>      )
> gives another results:
> 1. object file has 159044 bytes size
> 2. in disassembler a lot of unnecessary .objc_property_list,       .objc_method_list, .objc_protocol_list and .objc_protocol  in .bss       and .data section
> 3. the final binary size is 101837 bytes size
> 
> 
> 
> If comment in above sample #import <UIKit/UIKit.h, the size of       object file and binary file in xcode compilation will be the same,
> but size binary and object file in case of       clang+llvm-3.8.0-x86_64-apple-darwin compilation will be reduced       sufficiently:
> binary 28569 and object 36952 accordingly.
> 
> 
> 
> Looks like all protocols from UIKit.h is placed into       binary/object even it's not used there.
> I got 3.9.0 from public git (branch release_39 of clang git       repository) and found that all protocols interpret as definition       (isThisDeclarationADefinition),
> and in CGObjCGNU.cpp it's placed into object file whenever it's       used or not. With the same open source compiler and       -fobjc-runtime=ios protocols are not putting into
> object file even in compilation for ELF (I used -target       arm-linux-gnueabi).
> I used default binutil linker, not llvm's ld.ldd, due to I have problem with relocation on ARM.
> I didn't use LTO, due to my linker doesn't have plugin support (I didnt' yet recompile it).
> 
> Could somebody point me where to solve that problem, is it AST       generation stage, or linkage stage or maybe it's not a problem and just LTO could be solution here?
> 
> 
> 
> 
> p.s. It's not only one issue found by me in gnustep runtime       generation, and I'll report these issues in next emails.
> 
> 
> 
> 
> 
>         Best regards,
>        Alexey Perevalov
> 
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