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 20 struct bug { int t[sizeof(long) > 4 ? 1 : -1]; }; 21 int 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
