gcc + asm + on-stack iovec = uninitialized memory

gccbug.c

// Compile at -O0 and -O1 or higher and compare the output of
// `strace -e pwritev a.out`. At -O0:
//
//    pwritev(1, [{"Hello ", 6}, {"world!", 6}, {"\n", 1}], 3, 0) = -1 ESPIPE
//    (Illegal seek)
//
// At -O1 or higher:
//
//    pwritev(1, [{"", 0}, {"H\211l$\330L\211d$\340H\215-\367\10 \0L\215%\350\10
//    \0H\211\\$\320L\211l"..., 4195360}, {"", 0}], 3, 0) = -1 ESPIPE (Illegal
//    seek)
//
// Adding "memory" to the clobber list fixes it. GCC 4.7.2 bug or not?

#include <sys/syscall.h>
#include <sys/uio.h>

int main(void)
{
  const struct iovec vec[] = {
    { .iov_base="Hello ", .iov_len=sizeof("Hello ") - 1 },
    { .iov_base="world!", .iov_len=sizeof("world!") - 1 },
    { .iov_base="\n",     .iov_len=1 }
  };
  long rval;
  __asm__ __volatile__ (
    "xor %%r10, %%r10;"
    "xor %%r8, %%r8;"
    "syscall;"
    : "=a" (rval)
    : "a" (SYS_pwritev), "D" (1), "S" (vec), "d" (3)
    : "%rcx", "%r11", "%r10", "%r8"
  );
  return 0;
}

Can't reproduce it on gcc 4.2.4.