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Re: overwriting default make rules

From: Duane Ellis
Subject: Re: overwriting default make rules
Date: Mon, 02 Mar 2009 21:50:24 -0500
User-agent: Thunderbird (Windows/20081209)

satyakam>Is it the right thing to do if i overwrite this rule as follows:

>      $(LD) $(LD_FLAGS) $(OBJECTS) $(LIBS) -o $static_link_file
> #   some more intermediate steps here...
>     $(POSLINK)  $(PL_FLAGS) $static_link_file -o $@

In those situations (ie: Embedded systems) I have done this instead, "do not make a program".

Why? Because Make's internal rules generally *THINK* very wrongly that you are building for the host system, not cross compiling.

In the past, I have created *SINGLE* makefile, that builds both HOST and TARGET things, I do that via "$(HOST_CC)" and $(CC)", I used AUTOCONF for the $(CC) [cross-compile] side of things (target features, etc) and used auto-conf to "configure" host tools in some reasonable way, is the host cygwin/linux/mac or what?

Some argue that those are "two different configurations... and you should do that with Autoconf + Makefiles + whatever". I think they are pedantic nut cases. Truth is yes it can be done, but it nearly impossible for _LEARN_ and _DUPLICATE_ . Yes, the people behind GCC did that - It's called a Canadian cross... look it up. Utterly amazing it works, Equally confusing to understand, and mind boggling to debug. **BUT** Yes it works. And only they have done that, and nobody else in their right mind has ever duplicated that work.

In contrast: Look at the Linux kernel and how it is built.

The kernel people take another (but similar) approach - much like what I did, they have TWO different $(CC) commands, one is the $(CC) which is the *TARGET* compiler, and $(HOSTCC), which is the *HOST* compiler, then there are $CFLAGS, and $HOSTCFLAGS, they *DONOT* make a program. They create something else "vmlinux"

In summary, I would do it like this:

$(PROGRAM).linker: $(OBJECTS) $(LIBS)
   $(LD) ... steps -$@

%.tmp1: %linker
   intermediate command to do Step 1
   Example: "elf2bin"

%.tmp2: %.tmp1
   intermediate command for step 2
   Example: "Adding a boot loader header binary"

%.symbian: %.tmp2
   final command for 'symbian files'

The above is what I have done (using autoconf), and it is quite similar to the Linux Kernel approach (which does not use autoconf).

You might even add a "deploy" target to your makefile that "connects to your symbian test device and downloads the application" - quite helpful (ie: Visual Studio, for WinCE - has a "deploy button" which downloads[deploys] your program[solution] to the device.)

I would *never* - as you describe, create a "$PROGRAM" using default make rules, the default make rules are *ONLY* good if (a) your target and (b) your build system are identical, that is not what you are doing.


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