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// Test program which explores whether lseek syscall (not llseek!)
// on x32 uses 64-bit offset argument.
// IOW: does _kernel_ truncate it on entry?
// The answer appears to be "no, full 64-bit offset is used".
// strace must show it correctly too - tricky if strace itself is x32 one!
//
// Build: x86_64-gcc -static -Wall -ox32_lseek x32_lseek.c
// Run: $ strace ./x32_lseek 2>&1 | grep lseek | grep 1250999896321
// lseek(0, 1250999896321, SEEK_SET) = 1250999896321
#define _GNU_SOURCE
#include <sys/types.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/syscall.h>
// Ensure we are compiling to 64 bits
struct bug { int t[sizeof(long) > 4 ? 1 : -1]; };
int main(int argc, char **argv)
{
long ofs = 0x12345678901;
errno = 0;
close(0);
if (open("/etc/passwd", O_RDONLY))
return 1;
long r = syscall(
(long) (__NR_lseek | 0x40000000), // make x32 call
(long) (0),
(long) (ofs),
(long) (SEEK_SET)
);
printf("pos:%ld(0x%lx) errno:%m\n", r, r);
if (!errno)
printf((r == ofs) ? "64-bit offset used\n" : "Kernel truncated offset\n");
return 0;
}
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