Why does following makefile rebuilt target "build" everytime - makefile

Question

I have the following code to untar all the files in a directory and move it to build directory. If I call make multiple times, it tries to execute "build" target everytime even if build directory already exists. Has anyone comes across this?
I found this question but it is not the same.
Makefile always running target
OS: Ubuntu 12.04
Program: GNU Make 3.81
build: mkBuildDir untar
chmod 700 build
.PHONY: mkBuildDir untar
mkBuildDir:
mkdir build
untar: *.tar.gz
for prefix in *.tar.gz; do \
tar xvf $$prefix --directory=build; \
done
clean:
rm -Rf build

Answer 1

This is pretty much the same as the question you've linked. You never create a file called mkBuildDir, so it's always out-of-date, so build is always out of date.
Your mkBuildDir target isn't doing anything useful (though I presume this is a cut-down makefile). If instead you did
# it'd be better to list the TARFILES explicitly, though this will probably work
TARFILES=`ls *.tar.gz`
all: build untar
build: $(TARFILES)
test -d build || mkdir build
chmod 700 build
for prefix in $(TARFILES); do \
tar xvf $$prefix --directory=build; \
done
clean:
rm -Rf build
that would probably accomplish what you're looking for.
Having too many phony targets in a Makefile is usually a makefile 'code smell'. They are rarely the best/idiomatic way of doing things.