[Qt-interest] Qt 4.4, Snow Leopard & QMAKE_COMP_QMAKE_OBJECTIVE_CFLAGS

[Dave Thorup]

Does anyone know where QMAKE_COMP_QMAKE_OBJECTIVE_CFLAGS get defined?   
I greped through the entire Qt 4.4.3 source tree and couldn't find a  
definition anywhere.  Although it appears in many of the Makefiles  
that are created when building Qt from source I can't seem to find  
where it's actually defined.  The best I can find is in qt-mac- 
commercial-src-4.4.3/mkspecs/features/mac/objective_c.prf:

-----------------------------------------
isEmpty(QMAKE_OBJECTIVE_CC):QMAKE_OBJECTIVE_CC = $$QMAKE_CC
isEmpty(QMAKE_OBJECTIVE_CFLAGS) { #bootstrap
     QMAKE_OBJECTIVE_CFLAGS = $$QMAKE_CFLAGS
     QMAKE_OBJECTIVE_CFLAGS_WARN_ON = $$QMAKE_CFLAGS_WARN_ON
     QMAKE_OBJECTIVE_CFLAGS_WARN_OFF = $$QMAKE_CFLAGS_WARN_OFF
     QMAKE_OBJECTIVE_CFLAGS_DEBUG = $$QMAKE_CFLAGS_DEBUG
     QMAKE_OBJECTIVE_CFLAGS_RELEASE = $$QMAKE_CFLAGS_RELEASE
     QMAKE_OBJECTIVE_CFLAGS_X86 = $$QMAKE_CFLAGS_X86
     QMAKE_OBJECTIVE_CFLAGS_PPC = $$QMAKE_CFLAGS_PPC
     QMAKE_OBJECTIVE_CFLAGS_HIDESYMS = $$QMAKE_CXXFLAGS_HIDESYMS
}
OBJECTIVE_C_OBJECTS_DIR = $$OBJECTS_DIR
isEmpty(OBJECTIVE_C_OBJECTS_DIR):OBJECTIVE_C_OBJECTS_DIR = .
isEmpty(QMAKE_EXT_OBJECTIVE_C):QMAKE_EXT_OBJECTIVE_C = .mm .m

objective_c.dependency_type = TYPE_C
objective_c.variables = QMAKE_OBJECTIVE_CFLAGS
objective_c.commands = $$QMAKE_OBJECTIVE_CC -c $ 
(QMAKE_COMP_QMAKE_OBJECTIVE_CFLAGS) $(DEFINES) $(INCPATH) $ 
{QMAKE_FILE_IN} -o ${QMAKE_FILE_OUT}
objective_c.output = $$OBJECTIVE_C_OBJECTS_DIR/${QMAKE_FILE_BASE}$$ 
{first(QMAKE_EXT_OBJ)}
objective_c.input = OBJECTIVE_SOURCES
objective_c.name = Compile ${QMAKE_FILE_IN}
silent:objective_c.commands = @echo objective-c ${QMAKE_FILE_IN} && $ 
$objective_c.commands
QMAKE_EXTRA_COMPILERS += objective_c
-----------------------------------------

It is used here and there's a definition for QMAKE_OBJECTIVE_CFLAGS  
but no definition for QMAKE_COMP_QMAKE_OBJECTIVE_CFLAGS.

The problem is that Snow Leopard (Mac OS X 10.6) changes the default  
gcc version to be 4.2, but you can't use gcc 4.2 to build applications  
that target Mac OS X 10.4.  So when building Qt 4.4.3 under Snow  
Leopard I can set the CC & CXX environment variables to gcc-4.0 & g+ 
+-4.0 respectively and this lets me build Qt with gcc 4.0.  I also  
need to set the Mac SDK to 10.4 to properly target it.  Here is my Qt  
configure command:

./configure -nomake demos -nomake examples -dwarf2 -sdk /Developer/ 
SDKs/MacOSX10.4u.sdk -universal -no-webkit -no-phonon -no-dbus

This properly sets the SDK when compiling C & C++ files, however there  
are a few Objective-C++ files that are compiled by Qt and it appears  
that the SDK is not set at all when building these files.  For example  
in qt-mac-commercial-src-4.4.3/src/gui/Makefile.Debug:1175 we have the  
following:

	gcc-4.0 -c $(QMAKE_COMP_QMAKE_OBJECTIVE_CFLAGS) $(DEFINES) $(INCPATH)  
kernel/qcursor_mac.mm -o .obj/debug-shared/qcursor_mac.o

QMAKE_COMP_QMAKE_OBJECTIVE_CFLAGS is defined on line 879 as follows:

####### Custom Compiler Variables
QMAKE_COMP_QMAKE_OBJECTIVE_CFLAGS = -pipe \
		-fconstant-cfstrings \
		-g \
		-gdwarf-2 \
		-fvisibility=hidden \
		-fvisibility-inlines-hidden \
		-Wall \
		-W \
		-arch \
		ppc \
		-arch \
		i386

You'll note that there is no SDK specified in  
QMAKE_COMP_QMAKE_OBJECTIVE_CFLAGS.  This causes compile errors when  
building Qt on 10.6 because it appears that some of the 10.6 System  
Headers require gcc 4.2 and won't work with gcc 4.0.  The SDK is  
properly used when building C & C++ files as these commands use the  
CFLAGS & CXXFLAGS respectively which are defined at the top of the  
file and include "-isysroot /Developer/SDKs/MacOSX10.4u.sdk" in each  
of them to properly specify the 10.4 SDK.

I was able to get around this issue by manually adding the 10.4 SDK to  
the QMAKE_COMP_QMAKE_OBJECTIVE_CFLAGS definition in the few Makefiles  
that actually build Objective-C++ sources.  However I'd like to figure  
out how to fix it properly so that there will be less hassle when I  
need to build Qt 4.4.3 in the future on a different Snow Leopard  
machine.  Does anyone know where I could make a fix such that the SDK  
is properly specified when Qt compiles Objective-C++ files?

Thanks for any help.
--
Dave Thorup
Software Engineer
http://bibblelabs.com