My Program Keeps Failing With - Error While Loading Shared Libraries - c

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.