COMS 4995 Advanced Systems Programming

Index of 2024-9/code/17

Parent directory
Makefile
main-dlopen.c
main.c
mymalloc.c
sum.c

Makefile

CC=gcc
CFLAGS=-Wall -fpic

main-dyn: main.o libsum.so
	gcc  -o main-dyn main.o libsum.so

main-no-pie: main.o libsum.so
	gcc -no-pie  -o main-no-pie main.o libsum.so

main-static-pie: main.o sum.o
	gcc -static-pie  -o main-static-pie main.o sum.o

main-static: main.o sum.o
	gcc -static  -o main-static main.o sum.o

libsum.so: sum.o
	gcc -shared -o libsum.so sum.o

main.o sum.o:

.PHONY: clean
clean:
	rm -f *.o *.so a.out main-dyn main-no-pie main-static-pie main-static

.PHONY: all
all: clean main-dyn

main-dlopen.c

#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>

int main()
{
    void *handle = dlopen("libsum.so", RTLD_LAZY);
    if (!handle) {
        fprintf(stderr, "%s\n", dlerror());
        exit(1);
    }

    // clear any existing error
    dlerror();
    // declare func ptr to: long sum_array(long *p, int n);
    long (*f)(long *p, int n);

    f = dlsym(handle, "sum_array");

    char *error = dlerror();
    if (error != NULL) {
        fprintf(stderr, "%s\n", error);
        exit(1);
    }

    long a[5] = {0, 1, 2, 3, 4};
    long sum = f(a, 5);
    printf("sum=%ld\n", sum);

    dlclose(handle);
}

main.c

#include <stdio.h>

long sum_array(long *p, int n);

int main() {
    long a[5] = {0, 1, 2, 3, 4};
    long sum = sum_array(a, 5);
    printf("sum=%ld\n", sum);
}

mymalloc.c

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>

/* malloc wrapper function */
void *malloc(size_t size)
{
    void *(*mallocp)(size_t size);
    char *error;

    mallocp = dlsym(RTLD_NEXT, "malloc"); /* Get address of libc malloc */
    if ((error = dlerror()) != NULL) {
        fputs(error, stderr);
        exit(1);
    }

    char *ptr = mallocp(size); /* Call libc malloc */
    fputs("malloc wrapper called\n", stderr);
    return ptr;
}

/* free wrapper function */
void free(void *ptr)
{
    void (*freep)(void *) = NULL;
    char *error;

    if (!ptr) {
        return;
    }
    freep = dlsym(RTLD_NEXT, "free"); /* Get address of libc free */
    if ((error = dlerror()) != NULL) {
        fputs(error, stderr);
        exit(1);
    }

    freep(ptr); /* Call libc free */
    fputs("free wrapper called\n", stderr);
}

sum.c

long sum(long a, long b) {
    return a + b;
}

long sum_array(long *p, int n) {
    long s = 0;
    for (int i = 0; i < n; i++) {
        s = sum(s, p[i]);
    }
    return s;
}