1// Test program which explores whether lseek syscall (not llseek!)
2// on x32 uses 64-bit offset argument.
3// IOW: does _kernel_ truncate it on entry?
4// The answer appears to be "no, full 64-bit offset is used".
5// strace must show it correctly too - tricky if strace itself is x32 one!
6//
7// Build: x86_64-gcc -static -Wall -ox32_lseek x32_lseek.c
8// Run:   $ strace ./x32_lseek 2>&1 | grep lseek | grep 1250999896321
9//        lseek(0, 1250999896321, SEEK_SET) = 1250999896321
10#define _GNU_SOURCE
11#include <sys/types.h>
12#include <stdlib.h>
13#include <unistd.h>
14#include <errno.h>
15#include <sys/stat.h>
16#include <fcntl.h>
17#include <stdio.h>
18#include <sys/syscall.h>
19// Ensure we are compiling to 64 bits
20struct bug { int t[sizeof(long) > 4 ? 1 : -1]; };
21int main(int argc, char **argv)
22{
23	long ofs = 0x12345678901;
24	errno = 0;
25	close(0);
26	if (open("/etc/passwd", O_RDONLY))
27		return 1;
28	long r = syscall(
29		(long) (__NR_lseek | 0x40000000), // make x32 call
30		(long) (0),
31		(long) (ofs),
32		(long) (SEEK_SET)
33	);
34	printf("pos:%ld(0x%lx) errno:%m\n", r, r);
35	if (!errno)
36		printf((r == ofs) ? "64-bit offset used\n" : "Kernel truncated offset\n");
37	return 0;
38}
39