putc               38 user/printf.c      putc(fd, buf[i]);
putc               44 user/printf.c    putc(fd, '0');
putc               45 user/printf.c    putc(fd, 'x');
putc               47 user/printf.c      putc(fd, digits[x >> (sizeof(uint64) * 8 - 4)]);
putc               64 user/printf.c          putc(fd, c0);
putc               97 user/printf.c          putc(fd, va_arg(ap, uint32));
putc              102 user/printf.c            putc(fd, *s);
putc              104 user/printf.c          putc(fd, '%');
putc              107 user/printf.c          putc(fd, '%');
putc              108 user/printf.c          putc(fd, c0);