Q1.1 Alice wants to make fun of Bob. On Bob’s birthday, she replaces the cat program in Bob’s xv6 system with a patched version of cat that always prints Happy Birthday, Bob! no matter the input. Here is the original version of cat.c from the xv6 source tree: 1 #include "types.h" 2 #include "stat.h" 3 #include "user.h" 4 5 char buf[512]; 6 7 void 8 cat(int fd) 9 { 10 int n; 11 12 while((n = read(fd, buf, sizeof(buf))) > 0) { 13 if (write(1, buf, n) !...