[LTP] shmctl03.c is broken for 32bit compat mode

[Dan Carpenter]

In 32bit compat mode the shmctl03.c test will always fail:

shmctl03.c:33: TFAIL: /proc/sys/kernel/shmmax != 2147483647 got 4294967295
shmctl03.c:34: TPASS: /proc/sys/kernel/shmmni = 4096
shmctl03.c:35: TFAIL: /proc/sys/kernel/shmall != 4278190079 got 4294967295

The test basically does this:
// === === ===
#define _GNU_SOURCE
#include <sys/shm.h>
#include <stdio.h>

int main(void)
{
	struct shminfo info;

	shmctl(0, IPC_INFO, (struct shmid_ds *)&info);

	printf("shmmax = %lu\n", info.shmmax);
	printf("shmmni = %lu\n", info.shmmni);
	printf("shmall = %lu\n", info.shmall);

	return 0;
}
// === === ===

It compares that output with what we read from the file.  You can run
"gcc -m32 test.c && ./a.out" to see the issue.

In the first line shmmax is not the value that we read from the file
because it was capped at INT_MAX by the kernel in commit af7c693f1460
("Cap shmmax at INT_MAX in compat shminfo").
https://elixir.bootlin.com/linux/v6.16/source/ipc/shm.c#L1347

With the last line we're trying to store a u64 value into a u32.  We're
going to lose something so it's not going to be accurate.  The difference
is how scanf() truncates it.  If you have 32bit longs then it will give
you the first u32 but if you assign a u64 to a u32 like the rest of the
code does then you'll get the last 32 bits.

What's the right way to go about fixing this?

regards,
dan carpenter