Weak symbol

host.sh

#!/bin/sh
gcc -shared -fPIC sub.c -o libhost.so
gcc main.c -L. -lhost -o host
LD_LIBRARY_PATH=. ./host

main.c

int x = 1;
void f(void);
int main(void) {
    f();
    return 0;
}

sub.c

#include <stdio.h>
extern int x __attribute__((weak));
void f(void) {
    printf("x = %d\n", x);
}

target.sh

#!/bin/sh
arm-linux-androideabi-gcc -shared -fPIC sub.c -o libtarget.so
arm-linux-androideabi-gcc main.c -L. -ltarget -o target
adb shell rm -r /data/tmp
adb shell mkdir /data/tmp
adb push libtarget.so /data/tmp
adb push target /data/tmp
adb shell '(cd /data/tmp; LD_LIBRARY_PATH=. ./target)'