diff options
Diffstat (limited to 'test')
-rw-r--r-- | test/x32_lseek.c | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/test/x32_lseek.c b/test/x32_lseek.c new file mode 100644 index 0000000..6faa2fa --- /dev/null +++ b/test/x32_lseek.c @@ -0,0 +1,38 @@ +// 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; +} |