[cfe-users] objc object file generated for gnustep runtime for ELF target is too big

Perevalov Alexey via cfe-users cfe-users at lists.llvm.org
Mon Sep 26 06:33:11 PDT 2016

Dear community,

I'm using gnustep runtime -fobjc-runtime=gnustep with       gnustep-libobjc2 (https://github.com/gnustep/libobjc2) and
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
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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