Why does system call fails? - linux

Question

I try to compile simple utility (kernel 3.4.67), which
all it does is trying to use system call very simply as following:
int main(void)
{
int rc;
printf("hello 1\n");
rc = system("echo hello again");
printf("system returned %d\n",rc);
rc = system("ls -l");
printf("system returned %d\n",rc);
return 0;
}
Yet, system call fails as you can see in the following log:
root#w812a_kk:/ # /sdcard/test
hello 1
system returned 32512
system returned 32512
I compile it as following:
arm-linux-gnueabihf-gcc -s -static -Wall -Wstrict-prototypes test.c -o test
That's really wierd becuase I used system in past in different linux and never had any issue with it.
I even tried another cross cpompiler but I get the same failure.
Version of kernel & cross compiler:
# busybox uname -a
Linux localhost 3.4.67 #1 SMP PREEMPT Wed Sep 28 18:18:33 CST 2016 armv7l GNU/Linux
arm-linux-gnueabihf-gcc --version
arm-linux-gnueabihf-gcc (crosstool-NG linaro-1.13.1-4.7-2013.03-20130313 - Linaro GCC 2013.03) 4.7.3 20130226 (prerelease)
EDIT:
root#w812a_kk:/ # echo hello again && echo $? && echo $0
hello again
0
tmp-mksh
root#w812a_kk:/ #
But I did find something interesting:
On calling test_expander() withing the main, it works OK. so I suspect that maybe system call try to find a binary which is not founded ?
int test_expander(void)
{
pid_t pid;
char *const parmList[] = {"/system/bin/busybox", "echo", "hello", NULL};
if ((pid = fork()) == -1)
perror("fork error");
else if (pid == 0) {
execv("/system/bin/busybox", parmList);
printf("Return not expected. Must be an execv error.n");
}
return 0;
}
Thank you for any idea.
Ran

Answer 1

The return value of system(), 32512 decimal, is 7F00 in hex.
This value is strangely similar to 0x7F, which is the result of system() if /bin/sh can not be executed. It seems there is some problem with byte ordering (big/little endian). Very strange.
Update: while writing the answer, you edited the question and pulled in something about /system/bin/busybox.
Probably you simply don't have /bin/sh.

Answer 2

I think I understand what happens
From system man page:
The system() library function uses fork(2) to create a child process
that executes the shell command specified in command using execl(3)
as follows:
execl("/bin/sh", "sh", "-c", command, (char *) 0);
But in my filesystem sh is founded only /system/bin , not in /bin
So I better just use execv instead. (I can't do static link becuase it's read-only filesystem)
Thanks,
Ran