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