Jam SubDir Rule

13 Jul 2001 18:25 jam

Introduction

Now we’ve built an MFC application and a DLL, we’d like to include them in the same build process. This is what Jam’s SubDir rule does.

In the top-level directory, i.e. jam-test, we place a Jamfile looking like this:

SubDir TOP ;

SubInclude TOP lib ;
SubInclude TOP apps ;

We also need to create an empty Jamrules file, in order to supress a warning. This is not a problem: we’ll probably be putting project-specific rules in there in a moment.

We also have to create corresponding Jamfile files for the other directories. The one in the apps directory looks like this:

SubDir TOP apps ;

SubInclude TOP apps mfc_exe ;

And we have to add SubDir invocations to the top of the original Jamfiles, so that they know where they are.

We run the build from the top-level directory:

S:\jam-test>jam -d2 -f /jam-test/Jambase
Compiler is Microsoft Visual C++
...found 116 target(s)...
...updating 8 target(s)...
C++ apps\mfc_exe\ChildFrm.obj

        cl /nologo  /c  /MTd /W3 /Gm /GX /ZI /Od /D WIN32 /D _DEBUG /D _WINDOWS /D _MBCS /D _USRDLL /D WIN32_D
LL_EXPORTS /MDd /W3 /Gm /GX /ZI /Od /D WIN32 /D _DEBUG /D _WINDOWS /D _AFXDLL /D _MBCS    /Foapps\mfc_exe\Chil
dFrm.obj  /Iapps\mfc_exe  /IP:\VStudio\VC98\include  /Tpapps\mfc_exe\ChildFrm.cpp

Command line warning D4025 : overriding '/MTd' with '/MDd'
ChildFrm.cpp

... etc. ...

Rc apps\mfc_exe\mfc_exe.res

        rc  /d _DEBUG /d _AFXDLL /l 0x809    /Fo apps\mfc_exe\mfc_exe.res  apps\mfc_exe\mfc_exe.rc

Link apps\mfc_exe\mfc_exe.exe

        link /nologo   /dll /incremental:yes /debug /machine:I386 /subsystem:windows /incremental:yes /debug /
machine:I386  /out:apps\mfc_exe\mfc_exe.exe   apps\mfc_exe\ChildFrm.obj apps\mfc_exe\MainFrm.obj apps\mfc_exe\
mfc_exe.obj apps\mfc_exe\mfc_exeDoc.obj apps\mfc_exe\mfc_exeView.obj apps\mfc_exe\StdAfx.obj  apps\mfc_exe\mfc
_exe.res

...updated 8 target(s)...

If we attempt to run the mfc_exe executable, we find that it’s “not a valid Win32 executable”. This would appear to be down to the /dll switch being passed to the linker: we’ve managed to build a DLL and give it a .exe extension.

This behaviour is down to the way that Jam runs. Unlike recursive make, jam loads all of the named and included Jamfiles into the same “namespace”. Thus, C++FLAGS and LINKFLAGS are persistant from one Jamfile to the next.

At this point, we do something we should have done before: Since we’re invoking our SharedLibrary rule to build the DLL, we should add the /dll switch to the linker command line at that point.

We also don’t like the “overriding ‘/MTd’ with ‘/MDd’” warning. At this point, we introduce the SUBDIRC++FLAGS rule. It’s like C++FLAGS, but the flags only stay in effect until the next SubDir rule. We should change the DLL and executable Jamfiles to use this. For example, mfc_exe\Jamfile looks like this:

SubDir TOP apps mfc_exe ;

SUBDIRC++FLAGS += /MDd /W3 /Gm /GX /ZI /Od /D "WIN32" /D "_DEBUG" /D "_WINDOWS" /D "_AFXDLL" /D "_MBCS" ;
LINKFLAGS += /subsystem:windows /incremental:yes /debug /machine:I386 ;
RCFLAGS += /d "_DEBUG" /d "_AFXDLL" /l 0x809 ;

Main mfc_exe : ChildFrm.cpp MainFrm.cpp mfc_exe.cpp mfc_exeDoc.cpp mfc_exeView.cpp StdAfx.cpp ;
Resource mfc_exe : mfc_exe.rc ;

We also note that the LINKFLAGS are accumulating. There’s (strangely) no SUBDIRLINKFLAGS corresponding to SUBDIRC++FLAGS, but it’s not a major problem. The flags only differ slightly, and that’s according to the exe/dll nature of the target. We can move them into Jambase:

rule MainFromObjects
{
	local _s _t ;

	# Add grist to file names
	# Add suffix to exe

	_s = [ FGristFiles $(>) ] ;
	_t = [ FAppendSuffix $(<) : $(SUFEXE) ] ;

	if $(_t) != $(<)
	{
	    DEPENDS $(<) : $(_t) ;
	    NOTFILE $(<) ;
	}

	# make compiled sources a dependency of target

	DEPENDS exe : $(_t) ;
	DEPENDS $(_t) : $(_s) ;
	MakeLocate $(_t) : $(LOCATE_TARGET) ;

	Clean clean : $(_t) ;

	<b>LINKFLAGS on $(_t) += /subsystem:windows /incremental:yes /debug /machine:I386 ;</b>
	Link $(_t) : $(_s) ;
}

rule SharedLibraryFromObjects
{
	local _s _t ;

	# Add grist to file names
	# Add suffix to dll

	_s = [ FGristFiles $(>) ] ;
	_t = [ FAppendSuffix $(<) : $(SUFSHR) ] ;

	if $(_t) != $(<)
	{
	    DEPENDS $(<) : $(_t) ;
	    NOTFILE $(<) ;
	}

	# make compiled sources a dependency of target

	DEPENDS exe : $(_t) ;
	DEPENDS $(_t) : $(_s) ;
	MakeLocate $(_t) : $(LOCATE_TARGET) ;

	Clean clean : $(_t) ;

	<b>LINKFLAGS on $(_t) += /dll /incremental:yes /debug /machine:I386 ;</b>
	Link $(_t) : $(_s) ;
}

Conclusions

That was easy enough. We’ve still got a couple of things to work out:

We’re not actually attempting to link the EXE with the DLL, so there’s no dependency established.
The resource compiler flags aren’t being reset. We’ve only got one resource script so far, so it’s not an issue yet.

You can find the source resulting from this here.