Merge pull request #21 from xuesongbj/feat/init

feat(init): add init notes

源码剖析/1.18/1. 初始化/1. 引导.md

@@ -0,0 +1,94 @@
+# 引导
+
+随意编译一个可执行程序。
+
+```go
+$ gdb test
+
+GNU gdb (Ubuntu 9.2-0ubuntu1~20.04.1) 9.2
+Copyright (C) 2020 Free Software Foundation, Inc.
+
+Reading symbols from test...
+Loading Go Runtime support.
+
+(gdb) starti
+Starting program: test 
+
+Program stopped.
+_rt0_amd64_linux () at /usr/local/go/src/runtime/rt0_linux_amd64.s:8
+8       JMP _rt0_amd64(SB)
+```
+
+ 
+
+也可用 `readelf` 获取起始地址。
+
+```go
+$ readelf -h ./test
+
+ELF Header:
+  Entry point address:               0x453860
+
+
+$ addr2line -e ./test -a 0x453860
+
+/usr/local/go/src/runtime/rt0_linux_amd64.s:8
+```
+
+ 
+
+查看 `go/src/runtime` 目录下以汇编实现的引导过程源码。
+
+```go
+// rt0_linux_amd64.s
+
+TEXT _rt0_amd64_linux(SB),NOSPLIT,$-8
+    JMP _rt0_amd64(SB)
+```
+
+```go
+// asm_amd64.s
+
+// _rt0_amd64 is common startup code for most amd64 systems when using
+// internal linking. This is the entry point for the program from the
+// kernel for an ordinary -buildmode=exe program. The stack holds the
+// number of arguments and the C-style argv.
+
+TEXT _rt0_amd64(SB),NOSPLIT,$-8
+    MOVQ    0(SP), DI   // argc
+    LEAQ    8(SP), SI   // argv
+    JMP runtime·rt0_go(SB)
+```
+
+ 
+
+核心流程是创建 `main goroutine(runtime.main)`，并执行 `mstart` 进入调度循环。
+
+```go
+TEXT runtime·rt0_go(SB),NOSPLIT|TOPFRAME,$0
+
+    CALL    runtime·check(SB)
+
+    CALL    runtime·args(SB)
+    CALL    runtime·osinit(SB)
+    CALL    runtime·schedinit(SB)
+
+    // create a new goroutine to start program
+    MOVQ    $runtime·mainPC(SB), AX     // entry
+    PUSHQ   AX
+    CALL    runtime·newproc(SB)
+    POPQ    AX
+
+    // start this M
+    CALL    runtime·mstart(SB)
+
+    CALL    runtime·abort(SB)   // mstart should never return
+    RET
+```
+
+```go
+// mainPC is a function value for runtime.main, to be passed to newproc.
+
+DATA    runtime·mainPC+0(SB)/8,$runtime·main<ABIInternal>(SB)
+GLOBL   runtime·mainPC(SB),RODATA,$8
+```