Re: Request for review of failing makefile

[Maxim Yegorushkin]

On 17/12/09 16:06, David Aldrich wrote:
> Hi
> I have a problem with my makefile and would appreciate a peer review
> please.
> The makefile builds an .exe file from C++ source code and a static
> library. The static
> library has its own separate makefile. I find that if I touch a source
> file component
> of the static library and then execute the makefile below, the source
> file is
> compiled and the library is rebuilt, but the executable is not rebuilt.
> Running the
> same makefile a second time rebuilds the executable.
> Here's the code:
> ================================================================
> TRUNKDIR := ..
> EXEFILE := myapp
> include $(TRUNKDIR)/MakeVars.mk
> # Include the kernel and other static libraries as required
> STATIC_LIBS := $(TRUNKDIR)/Kernel
> .PHONY : release
> release : $(OBJDIR_R)/$(EXEFILE)
> # Generate the list of archives to be linked from the library paths
> specified in STATIC_LIBS
> ARCHIVES_R = $(patsubst %,%/$(OBJDIR_R)/lib.a,$(STATIC_LIBS))
> # Perform link (release mode)
> $(OBJDIR_R)/$(EXEFILE) : $(ARCHIVES_R)
> $(CXX) -o $(OBJDIR_R)/$(EXEFILE) -ldl -Wl,-whole-archive,-export-dynamic
> $(ARCHIVES_R) $(EXTRA_LIBS_R) -Wl,--no-whole-archive
> $(ARCHIVES_R) : $(STATIC_LIBS)
> .PHONY : $(STATIC_LIBS)
> $(STATIC_LIBS) :
> @$(MAKE) --quiet --directory=$@ $(MAKECMDGOALS)
> ================================================================

The above says that $(ARCHIVES_R) depend on a phony target 
$(STATIC_LIBS). What it does not say is how to update $(ARCHIVES_R), so 
that make considers $(ARCHIVES_R) to be always up-to-date, although its 
phony dependency always gets rebuild.

You can quickly check if my hypothesis is correct by adding an empty 
command to $(ARCHIVES_R), e.g.

$(ARCHIVES_R) : $(STATIC_LIBS)
        @echo "updated $@"

Although this won't solve the problem since now make considers that 
$(ARCHIVES_R) is always gets rebuild, triggering relinking 
$(OBJDIR_R)/$(EXEFILE) all the time.

The real problem is that the dependencies of $(ARCHIVES_R) are unknown, 
so that make can not know whether $(ARCHIVES_R) needs to be rebuild. 
This is a well-known problem with recursive makefiles that the 
dependency graph is incomplete.

A (classical) fix, without abandoning the recursive model, is to execute 
$(ARCHIVES_R) makefile first and then the makefile which builds 
$(OBJDIR_R)/$(EXEFILE).

  $ make --directory=$(STATIC_LIBS) && make

--
Max