Makefile library prerequisite
I have a makefile, which I am using to cross-compile for and embeded ARM platform with gcc. Specifcally, I am using arm-none-eabi-gcc, but the same appiles to avr-gcc, msp430-gcc, etc. Typically when using make+gcc (and not cross compiling) I list libs as prerequisite as follows:
programA.elf: programA.o foo.o -lm ...etc
programB.elf: programB.o bar.o -lftdi ...etc
%.elf:
gcc $(LDFLAGS) -o $@ $^
Make handles this "-lsyntax" very nicely, and its very convienient if you are building multiple progams/targets and want to have a generic rule for linking. The problem I have run into durring cross-compiling is that arm-none-eabi-gcc obviously has a different libm.a than my system's gcc libm.so (for example), but Make doesn't know whats going on here and keeps trying to use the x86 libm instead of the ARM base one. I can get things to work by adding the line:
.LIBPATTERNS = /usr/lib/arm-none-eabi/newlib/lib%.a
but it seems kinda clunky and exposes anyone wanting to compile the project to knowing a little more about the toolchain's install locations than is normally expected.
My question is: "Is there a better convention to list a binary's lib dependencies I should be using here that wont break when cross-compiling?"
This can be done. But a general solution is complex. I have Makefiles which build arm, x86, and c67 executables from a single set of sources. The page you reference eludes to the key: VPATH. I suggest a separate subdirectory for each architecture. The following is not working code, but it gives the idea
all: arm/pgma x86/pgma
vpath %.c $(CURDIR)
arm x86:
mkdir -p $@
arm/pgma: arm/main.o arm/sub.o | arm
x86/pgma: x86/main.o x86/sub.o more.o | x86
arm/%: CC=arm-none-eabi-gcc
arm/%: CFLAGS += -march=armv7-a -mtune=corex-a8
x86/%: CC=gcc
arm/%: VPATH = /usr/lib/arm-none-eabi/newlib
# Notice, VPATH not needed for x86 since it is the native host
This entire concept can be extend to build dependency file is each subdirectory as well debug and release variants. I have not tried this with the -lfoo, but it should work. Eg,
arm/pgma: arm/main.o arm/sub.o -lmylib | arm
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