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+++ b/slides/2018/20180403/slide.md	Thu Apr 05 11:34:39 2018 +0900
@@ -0,0 +1,181 @@
+title: 近況報告
+author: Takahiro Shimizu
+profile:
+lang: Japanese
+
+# 今週の進捗
+
+- xv6をcloneして読み始めました
+    - [Xv6, a simple Unix-like teaching operating system](https://pdos.csail.mit.edu/6.828/2017/xv6.html)
+- 教科書もありました
+    - [xv6 a simple, Unix-like teaching operating system](https://pdos.csail.mit.edu/6.828/2017/xv6/book-rev10.pdf)
+- 木金で読み会をやる予定です
+
+# systemcall
+
+- `user.h` `usys.S`でそれぞれ定義されていました
+
+```c
+// system calls
+int fork(void);
+int exit(void) __attribute__((noreturn));
+int wait(void);
+int pipe(int*);
+int write(int, void*, int);
+int read(int, void*, int);
+int close(int);
+int kill(int);
+int exec(char*, char**);
+int open(char*, int);
+int mknod(char*, short, short);
+int unlink(char*);
+int fstat(int fd, struct stat*);
+int link(char*, char*);
+int mkdir(char*);
+int chdir(char*);
+int dup(int);
+int getpid(void);
+char* sbrk(int);
+int sleep(int);
+int uptime(void);
+```
+
+# printf
+
+- printfは `%d, %x, %p, %s.` のみをサポートしています
+- コンパイラ構成論で書いたような素朴な実装でした
+- print時の進数は `printint` の引数で分けているようです
+
+```c
+void
+printf(int fd, char *fmt, ...)
+{
+  char *s;
+  int c, i, state;
+  uint *ap;
+
+  state = 0;
+  ap = (uint*)(void*)&fmt + 1;
+  for(i = 0; fmt[i]; i++){
+    c = fmt[i] & 0xff;
+    if(state == 0){
+      if(c == '%'){
+        state = '%';
+      } else {
+        putc(fd, c);
+      }
+    } else if(state == '%'){
+      if(c == 'd'){
+        printint(fd, *ap, 10, 1);
+        ap++;
+      } else if(c == 'x' || c == 'p'){
+        printint(fd, *ap, 16, 0);
+        ap++;
+      } else if(c == 's'){
+        s = (char*)*ap;
+        ap++;
+        if(s == 0)
+          s = "(null)";
+        while(*s != 0){
+          putc(fd, *s);
+          s++;
+        }
+      } else if(c == 'c'){
+        putc(fd, *ap);
+        ap++;
+      } else if(c == '%'){
+        putc(fd, c);
+      } else {
+        // Unknown % sequence.  Print it to draw attention.
+        putc(fd, '%');
+        putc(fd, c);
+      }
+      state = 0;
+    }
+  }
+}
+```
+
+# sysemcallを呼ぶ前
+
+- まだ処理が追いきれていません。
+
+```
+static void
+printint(int fd, int xx, int base, int sgn)
+{
+  static char digits[] = "0123456789ABCDEF";
+  char buf[16];
+  int i, neg;
+  uint x;
+
+  neg = 0;
+  if(sgn && xx < 0){
+    neg = 1;
+    x = -xx;
+  } else {
+    x = xx;
+  }
+
+  i = 0;
+  do{
+    buf[i++] = digits[x % base];
+  }while((x /= base) != 0);
+  if(neg)
+    buf[i++] = '-';
+
+  while(--i >= 0)
+    putc(fd, buf[i]);
+} 
+```
+
+# putc
+
+- 素朴にwriteを読んでいる
+
+```
+static void
+putc(int fd, char c)
+{
+      write(fd, &c, 1);
+}
+
+```
+
+# sh
+
+- main関数
+- まずforkが入る
+- cd以外はparseしてrunする世界観のようです
+
+```C
+int
+main(void)
+{
+  static char buf[100];
+  int fd;
+
+  // Ensure that three file descriptors are open.
+  while((fd = open("console", O_RDWR)) >= 0){
+    if(fd >= 3){
+      close(fd);
+      break;
+    }
+  }
+
+  // Read and run input commands.
+  while(getcmd(buf, sizeof(buf)) >= 0){
+    if(buf[0] == 'c' && buf[1] == 'd' && buf[2] == ' '){
+      // Chdir must be called by the parent, not the child.
+      buf[strlen(buf)-1] = 0;  // chop \n
+      if(chdir(buf+3) < 0)
+        printf(2, "cannot cd %s\n", buf+3);
+      continue;
+    }
+    if(fork1() == 0)
+      runcmd(parsecmd(buf));
+    wait();
+  }
+  exit();
+}
+```