[cfe-users] [cfe-dev] clang does not emit Ivar class name when compiling libobjc2 on Linux (Mac and gcc Linux are OK)

[David Chisnall via cfe-users]

As I said on the libobjc2 bug report, please file a clang bug and assign it to me.

David

> On 14 Sep 2016, at 20:53, Lobron, David via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> 
> Hello cfe-users,
> 
> I'm working to get my the libobjc2 Objective-C runtime working on Linux with clang-3.8.0.  I'm running into a problem with a library of mine that does class introspection.  My ObjC code does type introspection by looping through the ivars of an object and calling ivar_getTypeEncoding on each to get the type of the ivar.  When I compile with gcc, the ivar type for non-primitive variables comes through as @"NSString", @"NSDictionary", etc.  This also works with clang on my Mac.  But when I compile with clang on Linux, I only get the @ character.  I verified that the call to class_copyIvarList on Linux does return a list of Ivar objects, but when I call ivar_getTypeEncoding on those objects on Linux, I only get @, rather than the class name.  I've copied my library's ObjC code below.  
> 
> I talked this over with the owners of libobjc2, and we were wondering if there is a flag I can pass to clang to instruct it to emit this class data.  I looked at lib/CodeGen/CGObjCGNU.cpp in the clang source tree, but it wasn't immediately clear what flag I could pass here.  It's possible that there's no such flag, and the non-Apple clang simply doesn't emit this data, but I'd be somewhat surprised if Apple had diverged that much.
> 
> Thanks in advance for any help you can give,
> 
> David
> 
> My library's introspection code, with a debug print statement:
> 
> Ivar *ivarList = class_copyIvarList(c, &ivarCount);
> for (i = 0; i < ivarCount; i++) {
>  Ivar ivar = ivarList[i];
>  const char *ivarCname = ivar_getName(ivar);
>  if (ivarCname != 0 && ivarCname[0] != '_') {
>     NSString *ivarName = [NSString stringWithUTF8String:ivarCname];
>     const char *ivarType = ivar_getTypeEncoding(ivar);                    
>     if (ivarType[0] == '@' && ivarType[1] == '"') {
>         NSString *className = [[[NSString alloc] initWithBytes: &ivarType[2]
>                              length: strlen(&ivarType[2])-1
>                         encoding: NSUTF8StringEncoding] autorelease];
>         Class c = NSClassFromString(className);
>         if (c == nil) {
>             NSLog(@"WARNING: unknown class name \"%@\" in declaration of %@", className, [self class]);
>         } else {
>             NSLog(@"DBG: Deduced class %@ from className %@", c, className);
> 
> With gcc and clang on the Mac, I get messages like this:
> 
> 2016-09-14 19:29:21.950 archiveserver[1015:1015] DBG: Deduced class NSSet from className NSSet
> 2016-09-14 19:29:21.950 archiveserver[1015:1015] DBG: Deduced class NSString from className NSString
> 2016-09-14 19:29:21.950 archiveserver[1015:1015] DBG: Deduced class NSString from className NSString
> 2016-09-14 19:29:21.950 archiveserver[1015:1015] DBG: Deduced class NSString from className NSString
> 2016-09-14 19:29:21.950 archiveserver[1015:1015] DBG: Deduced class NSDictionary from className NSDictionary
> 2016-09-14 19:29:21.950 archiveserver[1015:1015] DBG: Deduced class NSDictionary from className NSDictionary
> 2016-09-14 19:29:21.950 archiveserver[1015:1015] DBG: Deduced class NSArray from className NSArray
> 
> With clang on Linux, nothing is printed, because ivarType[1] is not a double quote, so the second if evaluates to false.
> 
> 
> 
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