possibly misaligned/aliased ivars?

[sheffler]

(not sure this is the right place to ask, but here goes)

Hello,

I am trying to use ObjC with ARC, libdispatch and blocks on Linux. I believe I am seeing a problem where ivars are referenced incorrectly, or are being aliased. I have tried to reduce the problem to a very small example.

Last year, using Ubuntu 12.04 and clang 3.4 I built and used ObjC and libobjc2 successfully. I am trying to recreate a similar working environment on Debian 8. I installed clang from 'apt-get'. It is version 3.5.

Here is the program that illustrates the problem. The arrays are there to illustrate that gnustep-base seems to be working. The ivars 'i' and 'j' are problematic.

// #import <Foundation/Foundation.h>

@interface Thing : NSObject
@property (readwrite) int i;
// @property int pad1;
// @property int pad2;
@property (readwrite) int j;
@property (readwrite) NSMutableArray * arr;
@end

@implementation Thing

- (id) init {
  if (self = [super init]) {
    _i = 5;
    _j = 17;
    _arr = [[NSMutableArray alloc] init];
    [_arr addObject:@"test1"];
    [_arr addObject:@"test2"];
  }
  return self;
}

@end

int main(int argc, char *argv[])
{

  NSLog(@"starting");

  NSMutableArray *thing = [[NSMutableArray alloc] init];
  [thing addObject:@"one"];
  [thing addObject:@"two"];
  [thing addObject:@"three"];
  NSLog(@"array:%@", thing);
  thing = [[NSMutableArray alloc] init];
  NSLog(@"array:%@", thing);

  Thing *t = [[Thing alloc] init];
  NSLog(@"Thing:%@", t);
  NSLog(@"i:%u", t.i);
  NSLog(@"j:%u", t.j);
  NSLog(@"arr:%@", t.arr);
}

• On my Ubuntu 14.04 install it prints this:

2016-11-10 08:40:43.315 errorexample2[13183:13183] starting
2016-11-10 08:40:43.330 errorexample2[13183:13183] array:(one, two, three)
2016-11-10 08:40:43.332 errorexample2[13183:13183] array:()
2016-11-10 08:40:43.332 errorexample2[13183:13183] Thing:<Thing: 0x193d1c0>
2016-11-10 08:40:43.332 errorexample2[13183:13183] i:5
2016-11-10 08:40:43.332 errorexample2[13183:13183] j:17
2016-11-10 08:40:43.332 errorexample2[13183:13183] arr:(test1, test2)

• On my Debian 8 install it prints this, the i and the j are aliased somehow, and they share the same value.

2016-11-10 08:38:46.121 errorexample2[26516:26516] starting
2016-11-10 08:38:46.122 errorexample2[26516:26516] array:(one, two, three)
2016-11-10 08:38:46.122 errorexample2[26516:26516] array:()
2016-11-10 08:38:46.122 errorexample2[26516:26516] Thing:<Thing: 0x1f1e070>
2016-11-10 08:38:46.123 errorexample2[26516:26516] i:17
2016-11-10 08:38:46.123 errorexample2[26516:26516] j:17
2016-11-10 08:38:46.123 errorexample2[26516:26516] arr:(test1, test2)

• If I put in the padding properties, then things get even stranger.

2016-11-10 08:46:46.126 errorexample2[26553:26553] starting
2016-11-10 08:46:46.127 errorexample2[26553:26553] array:(one, two, three)
2016-11-10 08:46:46.127 errorexample2[26553:26553] array:()
2016-11-10 08:46:46.127 errorexample2[26553:26553] Thing:<Thing: 0x9d5070>
2016-11-10 08:46:46.128 errorexample2[26553:26553] i:10303216
2016-11-10 08:46:46.128 errorexample2[26553:26553] j:10303216
2016-11-10 08:46:46.128 errorexample2[26553:26553] arr:(test1, test2)

• The recipe I've followed for building libobjc2 and libdispatch are as follows. I've repeated this a few times.

sudo apt -y install clang git ninja cmake libffi-dev libxml2-dev libgnutls28-dev libicu-dev libblocksruntime-dev libkqueue-dev libpthread-workqueue-dev autoconf libtool libjpeg-dev libtiff-dev libffi-dev libcairo-dev libx11-dev libxt-dev libxft-dev libc++-dev

export CC=clang
export CXX=clang

# Checkout sources
git clone https://github.com/nickhutchinson/libdispatch.git
git clone https://github.com/gnustep/libobjc2.git
git clone https://github.com/gnustep/make
git clone https://github.com/gnustep/base.git
git clone https://github.com/gnustep/gui.git
git clone https://github.com/gnustep/back.git

cd libdispatch
mkdir build; cd build
make
sudo -E make install

cd libobjc2
cmake ../ -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang -DCMAKE_ASM_COMPILER=clang -DTESTS=OFF
cmake --build .
sudo -E make install

export LDFLAGS=-L/usr/local/lib

cd make
./configure --enable-debug-by-default --with-layout=gnustep --enable-objc-nonfragile-abi
make
sudo -E make install
sudo ldconfig

cd base
make clean
./configure

export LD_LIBRARY_PATH=/usr/local/lib:/usr/GNUstep/Local/Library/Libraries

• Now build the program

clang -g -o errorexample2 -x objective-c -fobjc-runtime=gnustep-1.8.1 -v -I/usr/local/include/objc -I/usr/GNUstep/Local/Library/Headers -f
objc-arc errorexample2.m Journal.m -L/usr/local/lib -L/usr/GNUstep/Local/Library/Libraries -lobjc -lgnustep-base -ldispatch

Any ideas or pointers are appreciated.

Thanks

[davidchisnall]

This was a bug introduced recently. See: 25c7038.

If you're not using SSE or similar vectors, then 6b28593 should work correctly.

[sheffler]

David -
thanks so much for your quick response. That was indeed the problem.

I began the investigation with a larger program that was exhibiting very mysterious behavior. Using the commit you showed, it seems to be working correctly now.

Much Thanks!