gnustep/linux“你好世界”核心转储

Question

我关注了this gnustep setup。

源包含一个几乎为空的自动释放池。没有它，应用程序就像标准 c 一样工作。

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{
    @autoreleasepool {
        NSLog(@"Hello, World!");
    }

    return 0;
}

制作：

CC=clang
CXX=clang++

OPT_RELEASE=-O3 
OPT_DEBUG=-DDEBUG -g

INCLUDE=-I.
LIBRARY= -L/usr/local/lib

CFLAGS=`gnustep-config --objc-flags`  -fobjc-runtime=gnustep
LDFLAGS=`gnustep-config --base-libs` -fobjc-runtime=gnustep

SOURCES= hello.m

OBJECTS=$(SOURCES:.m=.o)

DEPENDENCIES=$(SOURCES:.m=.d)

EXECUTABLE=hello    

all: $(EXECUTABLE)

$(EXECUTABLE): $(OBJECTS) 
        $(CC) $(LIBRARY) $(LDFLAGS) $(OBJECTS) $(STATICLIBS) -o $@

%.o: %.m
    $(CC) $(CFLAGS) $(INCLUDE) -c $< -o $@

clean:
   rm -rf $(OBJECTS) $(EXECUTABLE) $(DEPENDENCIES) core

核心：

#0  0x0000000000000000 in ?? ()
#1  0x00007ffff71f5c06 in objc_autoreleasePoolPop () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#2  0x00007ffff7716753 in -[NSAutoreleasePool emptyPool] (self=0x77dd30, _cmd=0x7ffff7cf5010 <.objc_selector_list+128>) at NSAutoreleasePool.m:411
#3  0x00007ffff77168c4 in -[NSAutoreleasePool dealloc] (self=0x77dd30, _cmd=0x7ffff7cf4fa0 <.objc_selector_list+16>) at NSAutoreleasePool.m:729
#4  0x00007ffff771686c in -[NSAutoreleasePool release] (self=0x77dd30, _cmd=0x7ffff7cfc3c0 <.objc_selector_list+240>) at NSAutoreleasePool.m:722
#5  0x00007ffff7728ca9 in +[NSCalendarDate initialize] (self=0x7ffff7cfc1e0 <_OBJC_CLASS_NSCalendarDate>, _cmd=0x63b470) at NSCalendarDate.m:380
#6  0x00007ffff71e5e93 in objc_send_initialize () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#7  0x00007ffff71f3199 in objc_msg_lookup_sender () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#8  0x00007ffff71f2eb7 in slowMsgLookup () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#9  0x00007ffff71f5048 in objc_msgSend_fpret () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#10 0x00007ffff776d4c6 in +[NSDate initialize] (self=0x7ffff7d0afe0 <_OBJC_CLASS_NSDate>, _cmd=0x63b470) at NSDate.m:134
#11 0x00007ffff71e5e93 in objc_send_initialize () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#12 0x00007ffff71f3199 in objc_msg_lookup_sender () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#13 0x00007ffff71f2eb7 in slowMsgLookup () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#14 0x00007ffff71f5048 in objc_msgSend_fpret () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#15 0x00007ffff78cdb30 in +[NSUserDefaults initialize] (self=0x7ffff7d7b4a0 <_OBJC_CLASS_NSUserDefaults>, _cmd=0x63b470) at NSUserDefaults.m:563
#16 0x00007ffff71e5e93 in objc_send_initialize () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#17 0x00007ffff71f3199 in objc_msg_lookup_sender () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#18 0x00007ffff71f2eb7 in slowMsgLookup () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#19 0x00007ffff71f5048 in objc_msgSend_fpret () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#20 0x00007ffff780c632 in +[NSObject initialize] (self=0x7ffff7d3c460 <_OBJC_CLASS_NSObject>, _cmd=0x63b470) at NSObject.m:1144
#21 0x00007ffff71e5e93 in objc_send_initialize () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#22 0x00007ffff71e5b06 in objc_send_initialize () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#23 0x00007ffff71f3199 in objc_msg_lookup_sender () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#24 0x00007ffff71f2eb7 in slowMsgLookup () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#25 0x00007ffff71f5048 in objc_msgSend_fpret () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#26 0x00007ffff71f58df in initAutorelease () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#27 0x00007ffff71f56ad in objc_autoreleasePoolPush () from /usr/GNUstep/Local/Library/Libraries/libobjc.so.4.6
#28 0x0000000000400a14 in main (argc=1, argv=0x7fffffffdbe8) at hello.m:5

Answer 1

这是我的研究结果：

DeleteAutoreleasePool 在 libobjc2(arc.m) 中声明为 IMP，如果在 NSAutoreleasePool.m 中找不到有效的 arc autorelease-pool，则从 objc_autoreleasePoolPop 调用。

使用实际版本的 clang，NSAutoreleasePool 可以正确检测发布池的可用性。 （在capabilities.h中声明）

这解释了为什么 NSAutoreleasePool 起作用。

arc.m 反过来读取这个结果。如果结果是肯定的，它什么也不做，否则它会从 NSAutoreleasePool 调用引用计数方法（因此可以使用 GCC 和其他编译器）。

这个过程中的一个缺陷可以在 initAutorelease(arc.m) 中找到。这里使用 class_respondsToSelector 检测自动释放池的可用性。换句话说，类方法被用作特征标志（叹气）。

经过验证的方法定义如下：

#ifdef ARC_RUNTIME
...

/**
 * Indicate to the runtime that we have an ARC-compatible implementation of
 * NSAutoreleasePool and that it doesn't need to bother creating objects for   
 * pools.
*/
- (void)_ARCCompatibleAutoreleasePool {}
#else

这个函数的问题是：

• 它什么也不做。
• 它什么也不返回。

即使启用了调试，我也希望这个函数在编译期间被忽略，也不会作为库调用导出。

这解释了为什么 obj-arc (@autoreleasepool) 不适用于 clang 3.4+。

如果您只对您的 objc 项目使用 clang，您可以重写或简单地停用此检测方法。