Using Make, how to build multiple configuration in one make command - makefile

Question

Thanks for all your time and response -
Currently, we are using the nested build, multiple Makefiles, and individual subdirectories having their own Makefile, all are connected with a top-level Makefile. We are running
make xxxxx_yyyy_defconfig
make
this builds and creates an output file which is xxxxx.elf file. --- Till here everything works fine.
Now we are having multiple def-configs(around 50), I want to build all configurations using one "make all" command. is that possible?
This is not a simple case where we can put all "all: prog01 prog02 prog03" as every program needs to have a different configuration. Configuration can be achieved by using "make xxxxx_yyyy_defconfig". The output of "make config" is the .config file, which is used during the "make" command.
Based on .config file many variables are exported which is used at the subdirectory level.
So How can I build multiple configurations using a single "make all" command?
Environment - Ubuntu, Cross compile for ARM, output file xxxx.elf.
With the use of script and make file I am able to solve, But I have to solve only using Makefile.
in Makefile add one PHONY target
all:
./build_all.sh #shell script calling.
Created one shell script like this
#! /usr/bin/bash
echo "Make All"
for entry in `ls conf`; do
make $entry
wait
make
if [ $? -eq 0 ] ; then
for xxxfile in `ls xxx*_*` ; do
xxxdir=$(echo $xxxfile | cut -b yy-zz)
mkdir -p $xxxdir
mv $xxxfile $xxxdir/
done
else
break
fi
done

Answer 1

If you want to build several configurations you must do this out of tree in separate build directories (make O=/tmp/builds/foo foo_defconfig; make -C /tmp/builds/foo) to avoid conflicts. A shell script could do this as well as a Makefile but if you insist on using a Makefile you could try the following that assumes your source tree is in /src/kernel and you want to build configuration foo in /tmp/builds/foo; adapt to your needs:
$ pwd
/tmp/builds
$ cat Makefile
CONFIGS := uuuu_vvvv xxxx_yyyy ...
BUILD := /tmp/build
KERNEL := /src/kernel
.PHONY: $(CONFIGS) all
all: $(CONFIGS)
$(CONFIGS):
rm -rf $#
mkdir -p $(BUILD)/$#
$(MAKE) -C $(KERNEL) O=$(BUILD)/$# $#_defconfig
$(MAKE) -C $(BUILD)/$#
$ make