c++ - How can I compile a 32 bit program using a makefile

Question

I'm attempting to make 3 separate programs mem_1.exe, mem_2.exe and mem_3.exe. I need to make them 32 bit when I compile them and the error message does not seem to be reflecting what I am writing. Below is my makefile.

mem_1: memlayout.o mem_1.o
    gcc -o mem_1 memlayout.c mem_1.c  -ldl -m32

mem_2: memlayout.o mem_2.o
    gcc -o mem_2 memlayout.c mem_2.c -m32 -ldl

mem_3: memlayout.o mem_3.o
    gcc -o mem_3 memlayout.c mem_3.c -m32 -ldl


mem_1.o: mem_1.c 
    gcc -c -o mem_1  mem_1.c -m32

mem_2.o: mem_2.c 
    gcc -c -o mem_2  mem_2.c -m32

mem_3.o: mem_3.c 
    gcc -c -o mem_3  mem_3.c -m32
memlayout.o: memlayout.c
    gcc -c -o memlayout memlayout.c -m32
clean:
    rm -f mem_1.o mem_2.o mem_3.o memlayout.o *~

Everytime I attempt to run this makefile I get this error message

cc    -c -o memlayout.o memlayout.c
cc    -c -o mem_1.o mem_1.c
gcc -o mem_1.exe mem_1.o memlayout.o -m32 -ldl
/usr/bin/ld: i386:x86-64 architecture of input file `mem_1.o' is incompatible with i386 output
/usr/bin/ld: i386:x86-64 architecture of input file `memlayout.o' is incompatible with i386 output

Which doesn't seem to make sense since I am using the -m32 flag to make it a 32 bit. Can anyone explain what I'm doing wrong?

question from:https://stackoverflow.com/questions/66057566/how-can-i-compile-a-32-bit-program-using-a-makefile

Answer 1

I'd advise thinking of your makefile as code (since it is) and follow the standard advice to avoid repeating yourself.

It looks like you also have the flags a bit wrong. -m32 is a compiler flag. -ldl is a linker flag. If you're going to build for 32 bits, you need to tell both the compiler and the linker to built 32-bit files. No guarantee, but I think you want something on this general order:

CFLAGS = -m32
LFLAGS = -melf_i386 -ldl

mem_1: mem_1.o memlayout.o
    $(LD) $(LFLAGS) -o mem_1 mem_1.o memlayout.o

mem_2: mem_2.o memlayout.o
    $(LD) $(LFLAGS) -o mem_2 mem_2.o memlayout.o

mem_3: mem_3.o memlayout.o
    $(LD) $(LFLAGS) -o mem_3 mem_3.o memlayout.o

# You probably don't really need this--`make` will usually have it built-in:
.c.o:
    $(CC) -c $(CFLAGS) $<

Note: I'm old, so this is a sort of old-fashioned Makefile. Gnu recommends doing things a bit differently, but this should still work.