My Program Keeps Failing With - Error While Loading Shared Libraries

Question

I wrote a program "run_coffee.c" to implement fork() and exec() system calls. It fundamentally calls exec to start another process "coffee" built through "coffee.c" multiple times. The problem is I am running this program on cygwin64 in windows environment and it keeps failing with the following error - **

error while loading shared libraries: ?: cannot open shared object file: no such file or directory

**

I also ran cygcheck to see wether dependencies are being met or not. This is the output -

C:\cygwin64\home\Admin\run_coffee.exe C:\cygwin64\bin\cygwin1.dll

C:\Windows\system32\KERNEL32.dll

C:\Windows\system32\API-MS-Win-Core-RtlSupport-L1-1-0.dll

C:\Windows\system32\ntdll.dll C:\Windows\system32\KERNELBASE.dll

C:\Windows\system32\API-MS-Win-Core-ProcessThreads-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-Heap-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-Memory-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-Handle-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-Synch-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-File-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-IO-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-ThreadPool-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-LibraryLoader-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-NamedPipe-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-Misc-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-SysInfo-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-Localization-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-ProcessEnvironment-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-String-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-Debug-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-ErrorHandling-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-Fibers-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-Util-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Core-Profile-L1-1-0.dll

C:\Windows\system32\API-MS-Win-Security-Base-L1-1-0.dll

No error or unmet dependency showed up so I guess all dependencies are being met. So what is causing this problem? Please Help.

Here are the two programs -

coffee.c

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

int main(int argc, char *argv[])
{
    char  *w = getenv("EXTRA");
    if (!w)
        w = getenv("FOOD");
    if (!w)
        w = argv[argc-1];
    char *c = getenv("EXTRA");
    if (!c)
        c = argv[argc-1];
    printf("%s with %s\n", c, w);
    return 0;
}

run_coffee.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

struct food_options
{
    char *food;
    char *extra;
};

int main()
{
    int i;
    char **env;
    env[0] = (char*)malloc(sizeof(char) * 20);
    env[1] = (char*)malloc(sizeof(char) * 20);
    env[2] = (char*)malloc(sizeof(char) * 20);
    struct food_options *opts = (struct food_options *)malloc(sizeof(struct food_options) * 3);
    opts[0].food = "coffee";
    opts[0].extra = "donuts";
    opts[1].food = "fish";
    opts[1].extra = "chips";
    opts[2].food = "kabab";
    opts[2].extra = "parantha";



    for (i = 0; i < 3; i++)
    {
        pid_t pid = fork();
        if (pid == -1)
        {
            fprintf(stderr, "Cannot fork process. Fatal Error %s\n", strerror(errno));
            return 1;
        }

        else if (!pid)
        {
            sprintf(env[0], "FOOD=%s", opts[0].food);
            sprintf(env[1], "EXTRA=%s", opts[0].extra);
            env[2] = NULL;
            if (execle("coffee.exe","coffee.exe",NULL,env) == -1)
            {
                fprintf(stderr, "Cannot execute coffee.exe. Error %s\n", strerror(errno));
            }
        }
    }
    free(opts);
    free(env[0]);
    free(env[1]);
    free(env[2]);
    return 0;
}

Answer 1

There is a memory bug in your program which can cause undefined behavior: you declared env to be an array of char*'s, but you did not initialize env. Hence, env[0], env[1], and env[2] point to random locations in memory. When you do sprintf(env[0], ...) and sprintf(env[1], ...), you are writing data to some random location in memory (where ever env[0] and env[1] points to). This can cause almost anything to happen, including modification of the names of libraries, making you unable to load them.