CROSS_PREFIX not always set from CLI

[2bndy5]

Recently, I had to try cross-compiling pigpio in a github CI workflow, but I didn't want to bother modifying the Makefile. According to the Makefile: https://github.com/joan2937/pigpio/blob/c33738a320a3e28824af7807edafda440952c05d/Makefile#L2-L4

I thought that by setting an env var CROSS_PREFIX I wouldn't have to modify the Makefile, but that approach didn't take at all.

Then I tried make lib CROSS_PREFIX='arm-linux-gnueabihf-', and that seemed to work until it executed https://github.com/joan2937/pigpio/blob/c33738a320a3e28824af7807edafda440952c05d/Makefile#L59-L60 as if $(CC) was set to gcc (without using the CROSS_PREFIX).

Would using

CROSS_PREFIX ?= ''

be more applicable with no side-effects to typical expected usage (which I assume means modify the Makefile).

Here is the CI step used in the github workflow

     - name: provide pigpio
        run: |
          git clone https://github.com/joan2937/pigpio.git
          cd pigpio
          git fetch --tags
          latestTag=$(git describe --tags `git rev-list --tags --max-count=1`)
          git checkout $latestTag
          make lib CROSS_PREFIX='arm-linux-gnueabihf-'
          sudo make install

Here is the Makefile's output

arm-linux-gnueabihf-gcc -I /usr/local/include -O3 -Wall -pthread -fpic -c -o pigpio.o pigpio.c
arm-linux-gnueabihf-gcc -I /usr/local/include -O3 -Wall -pthread -fpic -c -o command.o command.c
arm-linux-gnueabihf-gcc -shared -pthread -Wl,-soname,libpigpio.so.1 -o libpigpio.so.1 pigpio.o command.o
ln -fs libpigpio.so.1 libpigpio.so
arm-linux-gnueabihf-strip --strip-unneeded libpigpio.so
arm-linux-gnueabihf-size     libpigpio.so
   text	   data	    bss	    dec	    hex	filename
 226387	   6128	 605780	 838295	  cca97	libpigpio.so
arm-linux-gnueabihf-gcc -I /usr/local/include -O3 -Wall -pthread -fpic -c -o pigpiod_if.o pigpiod_if.c
arm-linux-gnueabihf-gcc -shared -pthread -Wl,-soname,libpigpiod_if.so.1 -o libpigpiod_if.so.1 pigpiod_if.o command.o
ln -fs libpigpiod_if.so.1 libpigpiod_if.so
arm-linux-gnueabihf-strip --strip-unneeded libpigpiod_if.so
arm-linux-gnueabihf-size     libpigpiod_if.so
   text	   data	    bss	    dec	    hex	filename
  44380	   5052	  49248	  98680	  18178	libpigpiod_if.so
arm-linux-gnueabihf-gcc -I /usr/local/include -O3 -Wall -pthread -fpic -c -o pigpiod_if2.o pigpiod_if2.c
arm-linux-gnueabihf-gcc -shared -pthread -Wl,-soname,libpigpiod_if2.so.1 -o libpigpiod_if2.so.1 pigpiod_if2.o command.o
ln -fs libpigpiod_if2.so.1 libpigpiod_if2.so
arm-linux-gnueabihf-strip --strip-unneeded libpigpiod_if2.so
arm-linux-gnueabihf-size     libpigpiod_if2.so
   text	   data	    bss	    dec	    hex	filename
  55850	   5052	   1988	  62890	   f5aa	libpigpiod_if2.so
gcc -O3 -Wall -pthread   -c -o x_pigpio.o x_pigpio.c
gcc -o x_pigpio x_pigpio.o -L. -lpigpio -pthread -lrt
/usr/bin/ld: skipping incompatible ./libpigpio.so when searching for -lpigpio
/usr/bin/ld: cannot find -lpigpio
collect2: error: ld returned 1 exit status
make: *** [Makefile:60: x_pigpio] Error 1

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Ultimately, I found it easier to use CMake to cross-compile pigpio, but that solution seems dependent on community support.